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CHAPTER 5

2009 Marshall County Multi-Hazard Mitigation Plan


Chapter 5 — Risk Assessment

5.1 Federal Requirements for Risk Assessments
5.2 Summary of Plan Updates
5.3 Identification and Description of Hazards
5.4 Hazard Profiles
5.5 Summary of Hazards and Community Impacts
5.6 Vulnerability of Structures within Each Jurisdiction
5.7 Estimate of Dollar Losses to Vulnerable Structures
5.8 General Description of Land Uses and Development Trends
5.9 Repetitively-Damaged NFIP-Insured Structures
5.10 Risks that Vary Among the Jurisdictions
5.1 Federal Requirements for Risk Assessments

This chapter of the Plan addresses the Risk Assessment requirements of 44 CFR Section 201.6 (c)(2), as follows:

“201.6 (c)(2) A Risk Assessment that provides the factual basis for activities proposed in the strategy to reduce losses from identified hazards. Local risk assessments must provide sufficient information to enable the jurisdiction to identify and prioritize appropriate mitigation actions to reduce losses from identified hazards. The risk assessment shall include:

(i) A description of the type, location, and extent of all natural hazards that can affect the jurisdiction. The plan shall include information on previous occurrences of hazard events and on the probability of future hazard events.

(ii) A description of the jurisdiction’s vulnerability to the hazards described in paragraph (c)(2)(i) of this section. This description shall include an overall summary of each hazard and its impact on the community. All plans approved after October 1, 2008 must also address NFIP insured structures that have been repetitively damaged by floods. The plan should describe vulnerability in terms of:

A. The types and numbers of existing and future buildings, infrastructure, and critical facilities located in the identified hazard areas;

B. An estimate of the potential dollar losses to vulnerable structures identified in paragraph (c)(2)(i)(A) of this section and a description of the methodology used to prepare the estimate;

C. Providing a general description of land uses and development trends within the community so that mitigation options can be considered in future land use decisions.

(iii) For multi-jurisdictional plans, the risk assessment section must assess each jurisdiction’s risks where they vary from the risks facing the entire planning area.”

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5.2 Summary of Plan Updates

Table 5-1 summarizes changes made to the 2004 plan as a result of the 2009 plan update, as follows:

Table 5-1. Summary of Plan Updates

Section Change
5.3 Identification and Description of Hazards Adds man-made hazards; identifies multi-hazards; describes sources
5.4 Hazard Profiles Improves descriptions of locations and extents; updates past occurrences; improves mapping
5.5 Summary of Hazards and Community Impacts Previously mentioned in hazard profiles; more community specific impact descriptions
5.6 Vulnerability of Structures within Each Jurisdiction A more comprehensive inventory of buildings, critical facilities, and infrastructure from HAZUS-MH; update of GIS data and mapping; improved methodologies; includes future conditions
5.7 Estimate of Dollar Losses to Vulnerable Structures Improved methodology and documentation; updated GIS mapping
5.8 General Description of Land Uses and Development Trends More extensive analysis; updates population and growth data; expands mapping
5.9 Repetitively-Damaged NFIP-Insured Structures Addresses new requirement
5.10 Risks that Vary Among the Jurisdictions Improved explanation of how risks vary
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5.3 Identification and Description of Hazards

5.3.1 Identification of Hazards Affecting Each Jurisdiction

Types of Hazards

The types of hazards affecting each Marshall County jurisdiction are listed in Table 5-2 “Identified Marshall County Hazards.” This table of identified hazards also notes multiple natural hazards that may be associated with and caused by certain hazard events. The 2004 Marshall County Natural Hazards Mitigation Plan lists the same natural hazards, except this 2009 plan update adds man-made hazards and identifies associated multi-hazard characteristics that are variations of the hazard or could occur as a direct consequence of the identified hazard.

Table 5-2. Identified Marshall County Hazards

Hazards Associated Hazards Jurisdictions Affected
Tornadoes High Winds
Severe Storms
Marshall County
Albertville
Arab
Boaz
Douglas
>Grant
Guntersville
Union Grove
Severe Storms Thunderstorms
Hail
Lightning
High Winds
Tornadoes
Floods
Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Floods
Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Hurricanes Tropical Storms
Tropical Depressions
Severe Storms
High Winds
Floods
Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Winter Storms/Freezes Snow Storms

Ice Storms

Extreme Cold

Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Droughts/Heat Waves Extreme Heat

Wildfires

Sinkholes

Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Wildfires Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Dam/Levee Failures Floods Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Landslides Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Earthquakes Landslides Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Sinkholes (Land Subsidence) Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Man-Made Hazards Marshall County
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove

Sources for Identifying Marshall County Hazards

The planning team used the following sources for identifying hazards in Marshall County:

1. HMPC Hazard Identification and Ratings Exercise. The Hazard Mitigation Planning Committee began the 2009 hazard identification process by completing an exercise to evaluate the list of hazards identified in the 2004 plan, which is reported in Appendix D ‘HMPC Hazard Identification and Ratings.’ A similar exercise was administered for the 2004 plan, and Appendix D compares the results.

2. 2007 Alabama State Plan. The 2007 update of the State Plan served as an additional resource for identifying local hazards. All of the hazards identified by the State were compared against the local list and differences were noted. Table 5-3 compares the hazards identified in this 2009 plan update to those identified in the 2007 Alabama State Plan and explains the differences. The State plan does not include man-made hazards.

Table 5-3. Comparison of Identified Marshall County Hazards to State Plan

Hazards Identified in 2007 Alabama State Plan Equivalent 2009 Marshall
County Identified Hazards
Differences
Floods
(storm surge, riverine, flash floods, etc.)
Floods No storm surge or coastal floods in Marshall County inland location.
High Winds
hurricanes, tornadoes and windstorms)
Tornadoes – High Winds
Severe Storms – High Winds
Hurricanes – High Winds
High winds included as components of tornadoes, severe storms, and hurricanes in Marshall County plan.
Winter/ice Storms Winter Storms/Freezes Marshall County plan identifies extreme cold as an associated hazard.
Landslides Landslides Marshall County plan identifies mudslides as an associated natural hazard.
Land Subsidence Sinkholes (Land Subsidence) Difference in terminology.
Earthquakes Earthquakes Marshall County plan identifies landslides as an associated natural hazard.
Droughts Droughts/Heat Waves Included as a component of droughts/heat waves in Marshall County plan. Marshall County plan identifies sinkholes as a consequence of droughts/heat waves.
Hail Severe Storms – Hail Included as a component of severe storms in Marshall County plan.
Wildfires Wildfires Marshall County plan associates wildfires with droughts/heat waves.
Extreme Temperatures Droughts/Heat Waves – Extreme Heat
Winter Storms/Freezes – Extreme Cold
Included as components of droughts/heat waves and winter storms/freezes in Marshall County plan.
Lightning Severe Storms – Lightning Included as a component of severe storms in Marshall County plan.
Dam Failures Dam/Levee Failures Marshall County plan associates floods with dam/levee failures.
Tsunamis None Marshall County is an inland location not subject to tsunamis.

3. List of Federally-Declared Disasters. Federal disaster declarations affecting Marshall County were an additional source for hazard identification. All declarations that have been issued since 1973 are included in the following table:

Table 5-4. 1973-2009 Federal Disaster Declarations Affecting Marshall County

Disaster No. Description Date Declaration Type*
369 Tornadoes, flooding 4/5/1973 IA,PA-ABCDEFG,DH,DUA,IFG
388 Severe storms, flooding 7/3/1973 IA,PA-ABCDEFG,DH,DUA,IFG
532 Severe storms, flooding 4/21/1977 IA,PA-ABCDEFG,DH,DUA,IFG
3045 Drought 8/16/1977 PA-AB
578 Severe storms, winds, flooding 4/18/1979 IA,DH,DUA,IFG
856 Flooding, severe storms, tornado 2/25/1990 IA,PA-ABCDEFG,DH,DUA,IFG
890 Flooding, severe storms 1/9/1991 IA,PA-ABCDEFG,DH,DUA,IFG
3096 Severe snowfall, winter storm 3/15/1993 PA-AB
1013 Winter storm, severe storms, freezing, flooding 3/3/1994 PA-ABCDEFG
1019 Severe storms, flooding, tornado 3/30/1994 IA,PA-ABCDEFG,DH,DUA,IFG
1047 Severe storms, flooding, tornadoes 4/21/1995 IA,PA-ABCDEFG,DH,DUA,IFG
1104 Severe storms, flooding 4/22/1997 IA,PA-ABCDEFG,DH,DUA,IFG
1399 Severe storms, tornadoes 12/7/2001 IA,CC,DH,DUA,IFG
1442 Severe storms, tornadoes 11/14/2002 IHP,CC,DUA
1466 Severe storms, tornadoes, flooding 5/12/2003 IA,DH
1549 Hurricane Ivan 9/15/2004 IA, PA-AB, HM
1593 Hurricane Dennis 7/10/2005 HM
1605 Hurricane Katrina 8/29/2005 HM
3237 Hurricane Katrina evacuation 9/10/2005 PA-AB
1687 Severe storms, tornadoes 3/3/2007 HM
3292 Hurricane Gustav 8/30/2008 SA, PA-B
1789 Hurricane Gustav 9/10/2008 HM
1797 Hurricane Ike 9/26/2008 HM
1835 Severe storms, winds, flooding, tornadoes 4/28/2009 HM
* Declaration Type Key
IA – Individual assistance A – Debris removal
PA – Public assistance B – Protective measures
DH – Disaster housing C – Roads and bridges
CC – Crisis counseling D – Water control facilities
DFA – Direct federal assistance E – Public buildings
DUA – Disaster unemployment assistance F – Public utilities
HM – Hazard mitigation G – Recreational
IFG – Individual and family grant SA – Stafford Act
SBA – Small Business Administration 403C – Department of Defense

Source: FEMA, Region IV

4. Other Hazard Identification Sources. Other sources for identifying hazards included the following resources:

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5.3.2 Tornadoes Description

Tornadoes are one of nature’s most violent storms, which are characterized by a rapidly rotating column of air extending from the base of a thunderstorm to the ground. In an average year, approximately 1,000 tornadoes are reported across the United States, resulting in over 1,500 injuries and 80 deaths, the greatest number of wind-related deaths. The most violent tornadoes, with wind speeds of 250 mph or more, are capable of tremendous destruction. Damage paths can be more than one mile wide and 50 miles long. Tornadoes can occur anywhere and come in all shapes and sizes.

In Alabama, peak tornado season is generally March through May with a secondary season in late fall; however, tornadoes can strike at any time of the year if the essential conditions are present. Tornadoes in the peak season are often associated with strong, frontal systems that form in central states and move east. Occasionally, large outbreaks of tornadoes occur with this type of weather pattern. Several states may be affected by numerous severe storms and tornadoes.

Tornadoes can occur in thunderstorms that develop in warm, moist air masses in advance of eastward-moving cold fronts. These thunderstorms often produce large hail and strong winds, in addition to tornadoes. Thunderstorms spawn tornadoes when cold air overrides a layer of warm air, causing the warm air to rise rapidly. Tornadoes occasionally accompany tropical storms and hurricanes that move over land. They are most common to the right and ahead of the path of the storm center as it comes onshore. The winds produced from wildfires have also been known to produce tornadoes.

The following graphic describes the formation of a tornado:

Figure 5-1. How a Tornado Forms

fig5-1_1.gif uparrowBefore thunderstorms develop, a change in wind direction and an increase in wind speed with increasing height create an invisible, horizontal spinning effect in the lower atmosphere. fig5-1_2.gif uparrowRising air within the thunderstorm updraft tilts the rotating air from horizontal to vertical. fig5-1_3.gif uparrowAn area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.
tornado4

Woodward OK (Ron Przybylinski)

uparrow A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This area is often nearly rain-free. Note rain in the background.
tornado4

Woodward OK (Ron Przybylinski)

uparrow Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also occurred with this storm.
Meteorologists rely on weather radar to provide information on developing storms. The National Weather Service is strategically locating Doppler radars across the country which can detect air movement toward or away from the radar. Early detection of increasing rotation aloft within a thunderstorm can allow life-saving warnings to be issued before the tornado forms.

When conditions are favorable for severe weather to develop, a severe thunderstorm or tornado WATCH is issued. Weather Service personnel use information from weather radar, spotters, and other sources to issue severe thunderstorm and tornado WARNINGS for areas where severe weather is imminent. Severe thunderstorm warnings are passed to local radio and television stations and are broadcast over local NOAA Weather Radio stations serving the warned areas. These warnings are also relayed to local emergency management and public safety officials who can activate local warning systems to alert communities.

In 1971, Dr. T. Theodore Fujita of the University of Chicago developed the original F-scale for wind damages, including tornadoes. The original F-scale, however, was recently replaced by an enhanced version effective February 1, 2007. The Enhanced F-scale is a more precise method of tornado damage assessment that classifies damage according to calibrations developed by engineers and meteorologists across 28 different types of damage indicators. The underlying premise is that a tornado scale needs to take into account the varying strengths and weaknesses of different types of construction. As with the original F-scale, the enhanced version rates the tornado as a whole based on most intense damage within the path. Historical tornadoes before February 1, 2007, will not be re-evaluated using the Enhanced F-scale.

Table 5-5. Enhanced F Scale for Tornado Damage

FUJITA SCALE

DERIVED EF SCALE

OPERATIONAL EF SCALE

F Number Fastest 1/4-mile (mph) 3 Second Gust (mph) EF Number 3 Second Gust (mph) EF Number 3 Second Gust (mph)
0 40-72 45-78 0 65-85 0 65-85
1 73-112 79-117 1 86-109 1 86-110
2 113-157 118-161 2 110-137 2 111-135
3 158-207 162-209 3 138-167 3 136-165
4 208-260 210-261 4 168-199 4 166-200
5 261-318 262-317 5 200-234 5 Over 200

Source: NOAA Storm Prediction Center’s On-Line Frequently Asked Questions about Tornadoes
( http://www.spc.noaa.gov/faq/tornado/#f-scale3)


Table 5-6. Fujita Tornado Damage Scale

SCALE

WIND ESTIMATE *** (MPH)

TYPICAL DAMAGE

F0

< 73

Light damage . Some damage to chimneys; branches broken off trees; shallow-rooted trees pushed over; sign boards damaged.

F1

73-112

Moderate damage . Peels surface off roofs; mobile homes pushed off foundations or overturned; moving autos blown off roads.

F2

113-157

Considerable damage . Roofs torn off frame houses; mobile homes demolished; boxcars overturned; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground.

F3

158-206

Severe damage . Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forest uprooted; heavy cars lifted off the ground and thrown.

F4

207-260

Devastating damage . Well-constructed houses leveled; structures with weak foundations blown away some distance; cars thrown and large missiles generated.

F5

261-318

Incredible damage . Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 meters (109 yds); trees debarked; incredible phenomena will occur.


(The description of tornadoes presented in this section is based upon information extracted from the FEMA How to Guides Understanding Your Risks (FEMA 386-2), FEMA, August 2001, and Using HAZUS-MH for Risk Assessment (FEMA 433), FEMA, August 2004, Tornadoes “ A Preparedness Guide , National Weather Service, February 1995, and the NOAA Storm Prediction Center’s On-Line Frequently Asked Questions about Tornadoes ( http://www.spc.noaa.gov/faq/tornado/#f-scale3 ).

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5.3.3 Severe Storms Description


Map 5-1. U.S. Average Thunderstorm Days per Year
Source: National Weather Service

Severe storms, as referred to in this plan, include severe thunderstorms with damaging lightning, hail, and straight-line winds. Severe storms are also associated with tornadoes, hurricanes, and floods, which are described separately in this plan.

Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. The typical thunderstorm is 15 miles in diameter and lasts an average of 30 minutes. Despite their small size, thunderstorms can be dangerous. Of the estimated 100,000 thunderstorms that occur each year in the United States, about 10 percent are classified as severe. The National Weather Service considers a thunderstorm severe if it produces hail at least 3/4-inch in diameter, winds of 58 mph or stronger, or a tornado.

Thunderstorms are formed by a combination of moisture to form clouds and rain, unstable air, that is, warm air that can rise rapidly, and lift from cold or warm fronts, sea breezes, mountains, or the sun’s heat which are capable of lifting air.

The National Weather Service estimates over 40,000 thunderstorms occur each day world-wide or close to 16 million annually. In the U.S., roughly 100,000 thunderstorms occur each year. The following map shows the average number of thunderstorm days each year throughout the U.S. The most frequent occurrence is in the southeastern states, with Florida having the highest incidence at 80 to 100+ thunderstorm days per year. Alabama’s incidence is high at 50 to 80 thunderstorm days per year. Warm, moist air from the Gulf of Mexico and Atlantic Ocean is most readily available to fuel thunderstorm development in this region of the country.

Figure 5-2. Life Cycle of a Thunderstorm

Developing Stage









Mature Stage


Dissipating Stage


Source: National Weather Service

Lightning results from the buildup and discharge of electrical energy between positively and negatively charged areas. Rising and descending air within a thunderstorm separates these positive and negative charges. Water and ice particles also affect charge distribution. A cloud-to-ground lightning strike begins as an invisible channel of electrically charged air moving from the cloud toward the ground. When one channel nears an object on the ground, a powerful surge of electricity from the ground moves upward to the clouds and produces the visible lightning strike.

Here are some facts about lightning from the National Weather Service:


Figure 5-3. Hail Stones.

Another damaging effect of severe storms is hail. Hail stones are large ice particles produced by intense thunderstorms. Strong rising currents of air within a storm, called updrafts, carry water droplets to a height where freezing occurs. Ice particles grow in size, becoming too heavy to be supported by the updraft, and fall to the ground. Large stones can fall at speeds faster than 100 mph. Hail causes substantial damage to property and crops each year in the U.S.

Most thunderstorm wind damage is caused by straight-line winds, which can exceed 100 mph. One type of straight-line wind, the downburst, is a small area of rapidly descending air beneath a thunderstorm. A downburst can cause damage equivalent to a strong tornado.


(The description of severe storms presented in this section is based upon information extracted from National Weather Service on-line publications at http://www.srh.noaa.gov/jetstream/tstorms/ ) .

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5.3.4 Floods Description

A flood is a natural event for rivers and streams. Excess water from snowmelt, rainfall, or storm surge accumulates and overflows onto the banks and adjacent floodplains. Floodplains are lowlands, adjacent to rivers, lakes, and oceans that are subject to recurring floods.

Hundreds of floods occur each year, making it one of the most common hazards in all 50 states and U.S. territories. Floods kill an average of 150 people a year nationwide. They can occur at any time of the year, in any part of the country, and at any time of day or night. Floodplains in the U.S. are home to over nine million households. Most injuries and deaths occur when people are swept away by flood currents, and most property damage results from inundation by sediment-filled water.

Several factors determine the severity of floods, including rainfall intensity (or other water source) and duration. A large amount of rainfall over a short time span can result in flash flood conditions. A small amount of rain can also result in floods in locations where the soil is saturated from a previous wet period or if the rain is concentrated in an area of impermeable surfaces such as large parking lots, paved roadways, or other impervious developed areas. Topography and ground cover are also contributing factors for floods. Water runoff is greater in areas with steep slopes and little or no vegetative ground cover. Frequency of inundation depends on the climate, soil, and channel slope. In regions where substantial precipitation occurs in a particular season each year, or in regions where annual flooding is derived principally from snowmelt, the floodplains may be inundated nearly every year. In regions without extended periods of below-freezing temperatures, floods usually occur in the season of highest precipitation. In areas where flooding is caused by melting snow, and occasionally compounded by rainfall, the flood season is spring or early summer.

Fortunately, most of the known floodplains in the United States have been mapped by FEMA, which administers the NFIP (National Flood Insurance Program). When a flood study is completed for the NFIP, the information and maps are assembled into a Flood Insurance Study (FIS). An FIS is a compilation and presentation of flood risk data for specific watercourses, lakes, and coastal flood hazard areas within a community and includes causes of flooding. The FIS report and associated maps delineate Special Flood Hazard Areas (SFHAs), designate flood risk zones, and establish base flood elevations (BFEs), based on the flood that has a 1% chance of occurring annually, or the 100-year flood. Paper FIRMs and FIS reports are gradually being replaced by DFIRMs (digital FIRMs).

The 100-year flood designation applies to the area that has a 1 percent chance, on average, of flooding in any given year. However, a 100-year flood could occur two years in a row, or once every 10 years. The 100-year flood is also referred to as the base flood. The base flood is the standard that has been adopted for the NFIP. It is a national standard that represents a compromise between minor floods and the greatest flood likely to occur in a given area and provides a useful benchmark.

Base Flood Elevation (BFE) , as shown on the FIRM, is the elevation of the water surface resulting from a flood that has a 1% chance of occurring in any given year. The BFE is the height of the base flood, usually in feet, in relation to the National Geodetic Vertical Datum (NGVD) of 1929, the North American Vertical Datum (NAVD) of 1988, or other datum referenced in the FIS report.

Special Flood Hazard Area (SFHA) is the shaded A-Zone or V-Zone area on a FIRM that identifies an area that has a 1% chance of being flooded in any given year or the 100-year floodplain. FIRMs show different floodplains with different zone designations, as shown on Table 5-7 “Flood Zone Designations.” These are used for insurance rating purposes, but are also necessary for flood permitting and flood hazard mitigation planning purposes. The 500-Year Floodplain is the shaded X-Zone area shown on a FIRM that has a 0.2% chance of being flooded in any given year.

Floodway is the stream channel and that portion of the adjacent floodplain that must remain open to permit passage of the base flood without substantial increases in flood heights. The Flood Fringe is the remainder of the 100-year floodplain.

The following graphic shows the components of a floodplain along a stream:

Figure 5-4. Flood Plain Cross Section

SSource: FEMA


Table 5-7. Flood Zone Designations

Flood Zones

A Zones

100-year floodplain areas of high risk.

 

A

The base floodplain mapped by approximate methods,
i.e., BFEs are not determined. This is often called an
unnumbered A zone or an approximate A zone.

 

AE

The base floodplain where base flood elevations are
provided.

 

AO

The base floodplain with sheet flow, ponding, or shallow flooding. Base flood depths (feet above ground) are provided.

 

AH

Shallow flooding base floodplain. BFEs are provided.

 

A99

Area to be protected from base flood by levees or
Federal flood protection systems under construction.
BFEs are not determined.

 

AR

The base floodplain that results from the de-certification of a previously accredited flood protection system that is in the process of being restored to provide a 100-year or greater level of flood protection.

V Zones

100-year coastal floodplain areas of high risk

 

V

The coastal area subject to a velocity hazard (wave
action) where BFEs are not determined on the FIRM.

 

VE

The coastal area subject to a velocity hazard (wave
action) where BFEs are provided on the FIRM.

X Zones

Areas of minimal to moderate risk outside the 100-year floodplain.

 

Shaded

Area of moderate flood hazard, usually the area between the limits of the 100-year and 500-year floods. Also includes areas protected by levees from the 100-year flood and shallow flooding areas with average depths of less than one foot or drainage areas less than 1 square mile.

 

Unshaded

Area of minimal flood hazard determined to be outside the 500-year floodplain.

D Zone

Area of undetermined but possible flood hazards.

Source: FEMA

A range of floods, other than just the 100-year flood, could happen within an area. Buildings in very close proximity to a stream or shore line, for example, might experience flooding much more frequently.


(The description of floods presented in this section is based upon information extracted from the FEMA How to Guide Understanding Your Risks(FEMA 386-2), FEMA, August 2001).

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5.3.5 Hurricanes Description


Figure 5-5. How a Hurricane Forms

Source: National Hurricane Center (www.nhc.noaa.gov)

Hurricanes, as referred to in this plan, include all types of tropical cyclones: hurricanes, tropical storms, and tropical depressions. A tropical cyclone is a rotating weather system that develops in the tropics. A tropical depression is an organized system of persistent clouds and thunderstorms with low level closed circulation and maximum sustained winds of 38 mph or less. A tropical storm is an organized system of strong thunderstorms with a well-defined circulation and maximum sustained winds of 39 to 73 mph. All of these tropical cyclones begin as a disturbance. A disturbance may result from a number of different weather events including Easterly Waves, West African Disturbance Line, Tropical Upper Tropospheric Trough or an Old Frontal Boundary. In order for a tropical disturbance to develop into a hurricane, three things must occur. First, the disturbance must gather energy and heat through contact with warm ocean waters. Next, added moisture evaporated from the sea surface then provides power to the tropical storm. And last, the seedling storm forms a wind pattern near the ocean surface that spirals inward. Warm water is the most important of the three, as it provides the fuel for a disturbance to eventually develop into a hurricane. A hurricane is a tropical weather system with a well defined circulation and sustained winds of 74 mph or higher. Even inland areas, well away from the coastline, can experience destructive winds, tornadoes and floods from tropical storms and hurricanes. 

The Atlantic hurricane season begins on June 1 and lasts through November. Within the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico annually there are an average of 11 tropical storms, 6 of which become hurricanes. In a typical three-year span, the US coastline is struck an average five times, two that are major hurricanes (category 3 or higher.) Hurricanes pose the greatest threat to life and property, but tropical depressions and storms can also cause extensive damage and loss of life. Hurricanes are categorized on a scale of 1 to 5 based on their sustained wind speed. Herbert Saffir, a consulting engineer in Coral Gables, Florida, and Dr. Robert Simpson, then director of the National Hurricane Center, developed this scale in the 1970's. Category 3-5 hurricanes are considered to be major storms. The Saffir-Simpson scale is based primarily on wind speeds and includes estimates of barometric pressure and storm surge associated with each of the five categories.



Table 5-8. Saffir-Simpson Scale

Category

Wind Speed

Storm Surge

(feet above normal sea level)

Expected Damage

1

74-95 mph

4-5 ft

Minimal : Damage is done primarily to shrubbery and trees, unanchored mobile homes are damage, some signs are damaged, no real damage is done to structures

2

96-110 mph

6-8 ft

Moderate : Some trees are toppled, some roof coverings are damaged, major damage is done to mobile homes

3

111-130 mph

9-12 ft

Extensive : Large trees are toppled, some structural damage is done to roofs, mobile homes are destroyed, structural damage is done to small homes and utility buildings.

4

131-155 mph

13-18 ft

Extreme : Extensive damage is done to roofs, windows, and doors; roof systems on small buildings completely fail, some curtain walls fail

5

>155 mph

>18 ft

Catastrophic : Roof damage is considerable and widespread, window and door damage is severe, there are extensive glass failures and entire buildings could fail.

Source: National Hurricane Center

The main parts of a hurricane are the eye, the eye wall, and rain bands. The eye of a hurricane is the calmest part. The eye is typically 20-40 miles across and has light winds that don’t exceed 15 mph. An eye will usually develop when the maximum sustained wind speed is more than 74mph. The strong rotation around the cyclone balances inflow to the center, causing air to ascend about 10-20 miles from the center forming the eyewall. A vacuum of air at the center is caused due to the strong rotation, the vacuum allows air flowing out of the top of the eyewall to turn inward and sink to replace the loss of air mass near the center. Due to the sinking air, cloud formation is suppressed. The passage of the eye is the calmest part of the hurricane. Since there is a light wind and fair weather, many believe that the storm has passed, which can prove dangerous. Immediately after the passage of the eye, the eyewall winds return but in an opposite direction.

The eyewall is the part of a hurricane where the strong winds meet the eye. The eyewall is a group of tall thunderstorms that produce heavy rain and the strongest winds within the storm. Changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm’s intensity. An eye may grow or shrink in size and additional eyewalls can form.

The rain bands are the outermost part of the hurricane. They are bands of clouds and thunderstorms that trail away from the eyewall in a spiral fashion. These bands produce heavy rain and strong winds, as well as tornadoes.

A hurricane also has additional hazards associated with it, both direct and indirect. The secondary hazards include storm surge, wind gusts, squalls, inland flooding and tornadoes. Storm surge is water that is pushed toward the shore by the winds around the storm. Storm surge combines with the normal tides to create the hurricane storm tide. Wind driven waves also combine into hurricane storm tide. The rise in water level can cause severe flooding in coastal areas. The level of surge is dependent upon the slope of the continental shelf. A shallow slope off of the coast allows a higher surge to inundate the area.

Figure 5-6. Storm Surge

Source: NWS Jet Stream- Online School for Weather at
www.srh.noaa.gov/srh/jetstream/tropics/tc_hazards.htm

In addition to storm surge, hurricanes are also known for damaging winds. They are rated according to their sustained wind speed. This scale does not account for gusts and squalls. Gusts are short and rapid bursts in wind speed. They are caused by turbulence over land mixing faster air aloft to the surface. Squalls are longer period of increased wind speeds; they are normally located within the outer rain bands.

Hurricanes, tropical storms, and depressions many times bring torrential rains and flooding. This flooding may last many days after the storm has passed. The strength of the storm does not always affect the level of flooding. A slow, weak tropical storm can cause more damage due to flooding than a more powerful fast moving hurricane.

Tornadoes also occur within a tropical cyclone. They are most likely to occur in the right-front quadrant of the storm, but can be embedded within the rain bands well away from the center of the storm. Some hurricanes produce no tornadoes, while others develop numerous ones. According to NOAA studies, half of all land falling hurricanes produce at least one tornado. The effects of a tornado, in addition to hurricane force winds, can produce substantial wind damages. A tornado can develop at any point during landfall, but normally occur within 12 hours after landfall, during daylight hours. Due to the likelihood of a tornado within a hurricane, a tornado watch is normally issued along the anticipated path of a hurricane before landfall.


(The description of hurricanes presented in this section is based upon information extracted from the NOAA publication Hurricanes Unleashing Nature’s Fury, A Preparedness Guide, Revised January 2007 at http://www.nws.noaa.gov/om/hurricane/pdfs/HurricanesUNF07.pdf and the NWS Jet Stream Online School for Weather at http://www.srh.noaa.gov/srh/jetstream/tropics/tropics_intro.htm ) .

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5.3.6 Winter Storms/Freezes Description

Winter storms and blizzards originate as mid-latitude depressions or cyclonic weather systems, sometimes following the meandering path of the jet stream. A blizzard combines heavy snowfall, high winds, extreme cold, and ice storms. The origins of the weather patterns that cause severe winter storms are primarily from four sources in the continental United States. Winter storms in the southeast region of the United States are usually a result of Canadian and Arctic cold fronts from the north and mid-western states combining with tropical cyclonic weather systems in the Gulf of Mexico. Typical winter storms in the Southeast include ice storms, crop-killing freezes and occasional snow.

Figure 5-7. Types of Winter Precipitation

fig5-7

Source: National Weather Service, Winter Storms, The Deceptive Killers at
http://www.weather.gov/os/winter/resources/winterstorm.pdf

Types of events that occur within a winter storm include freezing rain, sleet, blizzards, and frost/freeze. Freezing rain is rain that freezes when it hits the ground which coats roads, trees and power lines. Sleet is rain that turns into ice pellets before hitting the ground. A blizzard is snowfall with sustained winds or frequent gusts up to 35mph and considerable amounts of blowing snow. The expectation is that blizzard conditions will last 3 or more hours. Freezes occur when the temperatures will go below freezing. Many times frost/freezes cause substantial damage to crops. (The description of winter storms/freezes presented in this section is extracted from NOAA/NWS's publication Winter Storms, The Deceptive Killers, A Preparedness Guide at (http://www.weather.gov/os/winter/resources/winterstorm .pdf).

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5.3.7 Droughts/Heat Waves Description

A drought can occur almost anywhere, and its features vary from place to place depending on culture and geography. According to the National Drought Mitigation Center (NDMC), there are four ways of measuring drought. First is a meteorological drought, which is a decrease in precipitation in some period of time. These are usually region-specific, and based on a thorough understanding of regional climatology. Meteorological measurements are the first sign of drought. An agricultural drought occurs when there is not enough soil moisture to meet the needs of a particular crop at a particular time. Agricultural drought occurs after a meteorological drought, but before hydrological drought. Hydrological drought is deficiencies in surface and subsurface water supplies. It is measured as stream flow and at lake, reservoir and groundwater levels. There is a time lag between lack of rain and less water in rivers, streams, reservoirs and lakes. When precipitation is deficient over time, it will show in these water levels. The last type of drought defined by NDMC is a socioeconomic drought, which occurs when water shortages begin to affect people. In addition to the impacts discussed above, water level decline due to drought can also cause sinkholes to form.

The draft Alabama Drought Management Plan (2004) by the Office of Water Resources of the Alabama Department of Economic and Community Affairs (ADECA) explains the potential threats of droughts to Alabama and the need for effective drought planning and management, as follows:

In recent years, drought conditions have endangered Alabama’s water resources and adversely affected the livelihood of many people. Drought is a natural event that, unlike floods or tornadoes, does not occur in a violent burst but gradually happens; furthermore, the duration and extent of drought conditions are unknown because rainfall is unpredictable in amount, duration and location. The devastation (environmental, social, and economic) experienced in recent years due to drought conditions has not been successfully mitigated because previous responses to drought conditions at all levels of government has been slow and fragmented, with little focus on preparedness and mitigation. In an effort to be more proactive, the Office of Water Resources worked closely with numerous local, state, and federal agencies and other water resources professionals to develop and implement this statewide approach to drought planning and management.

The State drought plan establishes four phases of drought conditions – drought watch, advisory, warning, and emergency – identified by a compilation of drought indices, which include Crop Moisture Index, Palmer Drought Severity Index, Stream Flow, Reservoir Elevation Level, and Groundwater. Each of these phases requires varying levels of management. The U.S. Drought Monitor by the National Drought Mitigation Center (NDMC) uses a four-tier system to continuously monitor drought intensity based on another combination of drought indices. D1 is the first drought stage with severe conditions, and D4 is most intense drought stage with exceptional drought conditions. D0 includes drought watch areas that are abnormally dry and on the verge of drought or recovering from drought. The primary adverse physical effects of drought are classified as A (adverse impacts to agricultural crops, pastures, and grasslands) or H (adverse impacts to hydrologic resources for water supply, including rivers, reservoirs, and groundwater).

According to NOAA, extreme heat is the number one weather related killer taking an average of 1,500 people in the U.S. annually. The National Weather Service will issue watches and warnings when the heat index is expected to exceed 105°-110° F for at least two consecutive days. The heat index is given in degrees F and is a measure of how hot it really feels when the relative humidity is added to the actual air temperature.

Table 5-9. NOAA's National Weather Service Heat Index

Source: NOAA at http://www.weather.gov/om/heat/index.shtml


(The description of droughts/extreme heat presented in this section is extracted from: National Drought Mitigation Center, Defining Drought: Overview at http://drought.unl.edu/whatis/define.htm and NOAA, Heat Wave: A Major Summer Killer at http://www.noaawatch.gov/themes/heat.php ).

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5.3.8 Wildfires Description

Wildfires are a serious and growing hazard over much of the United States, posing great threats to life and property, particularly when moving from rural forest or rangeland into developed urban areas. Millions of acres burn every year in the United States as a result of wildfires, causing millions of dollars in damage. Each year more than 100,000 wildfires occur in the United States, almost 90 percent of which are started by humans; the rest are caused by lightning. Weather is one of the most significant factors in determining the severity of wildfires. The intensity of fires and the rate with which they spread is directly related to wind speed, temperature, and relative humidity. Climatic conditions, such as long-term drought, also play a major role in the number and the intensity of wildfires.

A wildfire is an uncontrolled fire spreading through vegetative fuels, exposing and possibly consuming structures. They often begin unnoticed and spread quickly and are usually signaled by dense smoke that fills the area for miles around. Naturally occurring and non-native species of grasses, brush, and trees fuel wildfires.

A wildland fire is a wildfire in an area in which development is essentially nonexistent, except for roads, railroads, power lines and similar facilities. An Urban-Wildland Interface fire is a wildfire in a geographical area where structures and other human development meet or intermingle with wildland or vegetative fuels.

States with a large amount of wooded, brush and grassy areas, such as Alabama, are at highest risk of wildfires. Additionally, areas anywhere that have experienced prolonged droughts or are excessively dry, are also at risk of wildfires.

People start more than four out of every five wildfires, usually as debris burns, arson, or carelessness. Lightning strikes are the next leading cause of wildfires.

Wildfire behavior is based on three primary factors:

The type, and amount of fuel, as well as its burning qualities and level of moisture affect wildfire potential and behavior. The continuity of fuels, expressed in both horizontal and vertical components is also a factor, in that it expresses the pattern of vegetative growth and open areas. Topography is important because it affects the movement of air (and thus the fire) over the ground surface. The slope and shape of terrain can change the rate of speed at which the fire travels. Weather affects the probability of wildfire and has a significant effect on its behavior. Temperature, humidity and wind (both short and long term) affect the severity and duration of wildfires.

Protecting Alabama’s rural areas from wildfire is the number one priority of the Alabama Forestry Commission. Wildfires burn thousands of acres of forestlands in Alabama every year. Through the efforts of the Forestry Commission and local volunteer fire departments, those wildfires are decreasing, but they still take a major toll on Alabama’s forest resources.

The Forestry Commission has a modern aggressive detection system that allows it to discover and suppress wildfires in the most efficient way possible. A fleet of airplanes regularly patrols over the forest and looks for wildfires. In addition, the public can report wildfires 24 hours a day through a toll-free telephone system. When a fire is reported, a dispatch center sends Forestry Commission crews and volunteer fire departments as needed to suppress it.

Volunteer fire departments are an essential part of the team when it comes to suppressing wildfires. The Forestry Commission works to help establish, train and maintain rural community fire departments in every county. This strong partnership of government and volunteer agencies working together provides cost efficient, effective fire service.

The Forestry Commission suppresses a wildfire by building a “fire break” which contains the fire by removing fuel from the fire so it cannot spread. These breaks are built using a bulldozer outfitted with a fire plow, which cuts a three foot wide trench across the site, removing all vegetation and exposing bare soil. On hilly sites, these firebreaks are built by hand using rakes and other tools by 20 person crews.

In extreme circumstances where several homes are threatened by a wildfire, the Forestry Commission can call in helicopters with large water buckets. These buckets do not put out the fire, but reduce its intensity so that the Commission crew can plow it out. The helicopter service is extremely expensive and is only done in severe fire conditions.


(The description of wildfires presented in this section is based upon information extracted from the FEMA How to Guides Understanding Your Risks (FEMA 386-2), August 2001, Using HAZUS-MH for Risk Assessment How to Guide (FEMA 433), August 2004, and the Alabama Forestry Commission at http://www.forestry.alabama.gov ).

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5.3.9 Dam/Levee Failures Description

Dam failure or levee failure can occur with little warning. Strong storms may produce a flood in a few hours or minutes for upstream locations, which can cause a dam or levee failure. Flash floods occur within six hours of the beginning of heavy rainfall and dam failure may occur within hours of the first sign of a breach. Dam failures are potentially the worst flood event. There are more than 80,000 dams in the United States according to the 2007 update of the National Inventory of Dams. According to FEMA, one third of these pose a high or significant hazard to life and property if failure occurs. 56% of dams are privately owned, and the dam owner is responsible for the safety and liability of the dam as well for upkeep, upgrade and repair. This compounds the risk that is posed due to dam or levee failure.


(The description of dam/levee failures presented in this section is extracted from FEMA, Disaster Types, Dam Failure at http://www.fema.gov/hazard/damfailure/index.shtm ).


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5.3.10 Landslides Description

Landslides occur and can cause damage in all 50 States, at an annual cost of about $3.5 billion per year (2005). Between 25 and 50 deaths per year in the U.S. are attributable to landslides. Landslides cause damage to the natural environment and economic losses, due to reduced real estate values, decreased agricultural and forestry productivity, among other adverse economic effects.

Severe storms, earthquakes, coastal wave attack, and wildfires can cause widespread slope instability and result in landslides. Landslide danger may be high, even as emergency personnel are providing rescue and recovery services for these other hazard events.

A landslide is a downward and outward movement of slope-forming soil, rock, and vegetation under the influence of gravity, which includes a wide range of ground movement. Numerous types of events, including natural and man-made changes within the environment, can trigger landslides. Examples of these changes that cause weaknesses in the composition or structures of the rock or soil include heavy rain, changes in ground water level, seismic activity, or construction activity. Man-made landslides may result from activities such as terracing, cut and fill construction, building construction, mining operations, and changes in irrigation or surface runoff.

There are different types of landslides. Rock falls are rapid movement of bedrock characterized by free-fall, bouncing and rolling. Slides are movements of soil or rock along a distinct surface of rupture that separates the slide material from the more stable underlying material. There are two major types of slides: rotational and translational slides. In a rotational slide the surface of rupture is curved concavely upward and the slide block rotates around an axis parallel to the slope contours. A translational slide is a mass that moves down and outward along a relatively planar surface with little rotational movement or backward tilting. Flows are mass movements of water-saturated material. The movement of flows can be extremely rapid (debris avalanche), very rapid (debris flow) or very slow (earth flow).

Here are some significant landslide facts from the USGS:


(The description of landslides presented in this section is extracted from the Geological Survey of Alabama, Geologic Hazards Section at http://www.gsa.state.al.us/gsa/geologichazards/landslides/index.html and the U.S.G.S. Landslides Hazards Program at http://landslides.usgs.gov ).

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5.3.11 Earthquakes Description

An earthquake is the shaking and vibration at the surface of the earth resulting from underground movement along a fault plane. Earthquakes are caused by the release of built-up stress within rocks along geologic faults or by the movement of magma in volcanic areas. They usually occur without warning and are usually followed by aftershocks. Earthquakes can affect hundreds of thousands of square miles and cause tens of billions of dollars of damage to property. An earthquake event can cause injury and loss of life to hundreds of thousands of persons and can greatly disrupt the social and economic functioning of the affected area. Secondary hazards during an earthquake may occur, such as surface faulting, sinkholes, and landslides.

Earthquakes are caused by the rupture or sudden movement of a fault where stresses have accumulated along opposing fault planes of the earth’s outer crust. These fault planes are usually found along the borders of the earth’s tectonic plates which generally follow the outlines of the continents. However, fault planes may occur at the interior of the plates. The plates range from 50 to 60 miles in thickness and move slowly and continuously over the earth’s interior. Where the plates move past each other, they continually bump, slide, catch, and hold. When the stress exceeds the elastic limit of the rock, an earthquake occurs. Generally, the larger the earthquake, the greater the potential for surface fault rupture.

The area of greatest seismic activity in the United States is along the Pacific coast in California and Alaska, but as many as forty states can be characterized as having at least moderate earthquake risk. For example, seismic activity has been recorded in Boston, Massachusetts; New Madrid, Missouri; and Charleston, South Carolina, places not typically thought of as earthquake zones. Areas prone to earthquakes are relatively easy to identify in the Western United States based on known geologic formations; however, predicting exactly when and where earthquakes will occur is very difficult everywhere. Records show that building inventories in 39 states are vulnerable to earthquake damage.

Most property damage and earthquake-related deaths result from the failure and collapse of structures caused by ground shaking or ground motion. Ground shaking is the motion felt on the earth’s surface caused by seismic waves generated by an earthquake. The strength of the ground shaking is determined by the magnitude of the earthquake, the surface distance from the earthquake’s epicenter and type of fault, and by the site and regional geology.

Ground shaking causes waves in the earth’s interior, known as seismic waves, and along the earth’s surface, known as surface waves. There are two types of seismic waves: primary waves which are longitudinal that cause back-and-forth oscillation along the direction of travel (vertical motion); and secondary waves or shear waves which are slower than primary waves and cause structures to vibrate from side-to-side (horizontal motion). Surface waves travel more slowly than and are usually significantly less damaging than seismic waves, illustrated by Figure 5-8. below.

Figure 5-8. Seismic and Surface Waves

SSource: FEMA


Additional earthquake related hazards include landslides, liquefaction, and amplification. Earthquake-induced landslides are secondary earthquake hazards that occur from ground shaking. They can destroy roads, buildings, utilities, and other critical facilities necessary to respond to or recover from an earthquake. As sloped lands are developed, earthquake-induced landslides pose additional threats to homes and infrastructure.

Soil type can substantially increase earthquake risk. Liquefaction occurs, when ground shaking causes saturated soft soils to change from a solid to a liquid state. Liquefaction results in the loss of soil strength and three potential types of ground failure: lateral spreading, flow failure, and loss of bearing strength. Buildings and their occupants are at risk when the ground can no longer support buildings and structures. Areas susceptible to liquefaction include areas with high ground water tables and sandy soils. The extreme earthquake damage to San Francisco in 1989 was due to liquefaction of the soil used to fill in waterfront properties.

Amplification (strengthening) of shaking also results in areas of soft soils which includes fill, loose sand, waterfront, and lake bed clays. Amplification increases the magnitude of the seismic waves generated by the earthquake.

Chart 5-1. Earthquake Magnitude Scale

Source: USGS

Seismic activity is described in terms of magnitude and intensity. Magnitude describes the total energy released and intensity describes the effects at a particular location. Magnitude is defined as the measure of the amplitude of the seismic wave and is expressed by the Richter scale. The Richter scale is a logarithmic measurement where an increase in the scale by one whole number represents a tenfold increase in the measured amplitude of the earthquake

Intensity is defined as the measure of the strength of the shock at a particular location and is expressed by the Modified Mercalli Intensity (MMI) scale. It was developed in 1931 by the American seismologists Harry Wood and Frank Neumann. The scale consists of a series of certain key responses such as people awakening, movement of furniture, the damage to structures, and total destruction. The lower numbers of the intensity scale generally deal with the manner in which the earthquake is felt by people. The higher numbers of the scale are based on observed structural damage. This scale, composed of 12 increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. It does not have a mathematical basis; instead it is an arbitrary ranking based on observed effects. Table 5-10 below compares the Modified Mercalli Intensity scale with the Richter scale.

Table 5-10. Earthquake Scales Comparison

 

Modified Mercalli Intensity and Richter Scale Comparison

SCALE

INTENSITY

DESCRIPTION OF EFFECTS

CORRESPONDING RICHTER SCALE MAGNITUDE

I

Instrumental

Detected only on seismographs

 

II

Feeble

Some people feel it

<4.2

III

Slight

Felt by people resting; like a truck rumbling by

 

IV

Moderate

Felt by people walking

 

V

Slightly Strong

Sleepers awake; church bells ring

<4.8

VI

Strong

Trees sway; suspended objects swing, objects fall off shelves

<5.4

VII

Very Strong

Mild Alarm; walls crack; plaster falls

<6.1

VIII

Destructive

Moving cars uncontrollable; masonry fractures, poorly constructed buildings damaged

 

IX

Ruinous

Some houses collapse; ground cracks; pipes break open

<6.9

X

Disastrous

Ground cracks profusely; many buildings destroyed; liquefaction and landslides widespread

<7.3

XI

Very Disastrous

Most buildings and bridges collapse; roads, railways, pipes and cables destroyed; general triggering of other hazards

<8.1

XII

Catastrophic

Total destruction; trees fall; ground rises and falls in waves

>8.1

Another measurement of seismic activity is Peak Ground Acceleration (PGA) which measures the rate of change of motion relative to the rate of acceleration due to gravity. An object falling to earth will fall faster and faster, until it reaches terminal velocity. This principle is known as acceleration and represents the rate at which speed is increasing. This movement can be described by its changing position as a function of time, or by its acceleration as a function of time. The peak acceleration is the maximum acceleration experienced by the object during the course of the earthquake motion. Peak ground acceleration can be measured in g (the acceleration due to gravity at the earth’s surface is 9.8 meters per second squared). For example, acceleration of the ground surface of 244 cm/sec/sec (where g equals 9.8 meters per second squared) equals a PGA of 25.0 percent.

Map 5-2 below shows the 2008 Peak Ground Acceleration (PGA) values for the southeast United States with a 2% chance of being exceeded over 50 years. This is a common earthquake measurement that shows three things: the geographic area affected (the areas shown in color), the probability of an earthquake at each given level of severity, and the severity (the PGA is indicated by color).


Map 5-2. 2008 PGA for Southeast
Peak Ground Acceleration with 2% Probability of Exceedance in 50 Years
Source: U.S. Geological Survey Earthquake Hazards Program


(The description of earthquakes presented in this section is based upon information extracted from the FEMA How to GuidesUnderstanding Your Risks (FEMA 386-2), August 2001, Using HAZUS-MH for Risk Assessment How to Guide (FEMA 433), August 2004, 2007 Alabama State Hazard Mitigation Plan, U.S. Geological Survey Earthquakes Hazard Program, and various FEMA-adopted plans).

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5.3.12 Sinkholes (Land Subsidence) Description

Sinkholes are a common, naturally occurring geologic feature that is hazardous to property and the environment. Although many new sinkholes develop naturally, their increasing frequency corresponds to the accelerated development of ground-water and land resources. Usually little more than a nuisance, new sinkholes can sometimes cause substantial property damage and structural problems for buildings and roads. See Figure 5-9 below, which shows the making of a sinkhole.

Figure 5-9. The Making of a Sinkhole

Source: Southwest Florida Water Management District


Sinkholes are common where the rock below the land surface is limestone, carbonate rock, salt beds, or rocks that can naturally be dissolved by ground water circulating through them. As the rock dissolves, spaces and caverns develop underground. Sinkholes are dramatic because the land usually stays intact for a while until the underground spaces get too big. If there is not enough support for the land above the spaces, then a sudden collapse of the land surface can occur. These collapses can be small or they can be huge and can occur where a house or road is on top. Figure 5-10 below illustrates the formation of a collapse.

Figure 5-10. Formation of a Collapse

Source: U.S. Geological Survey Mid-Continent Geographic Science Center

Sinkholes range in size from several square yards to hundreds of acres. They may be quite shallow or may extend hundreds of feet deep. The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. The picture in Figure 5-11 shows a sinkhole that quickly opened up causing major damage to a house and yard.


Figure 5-11. Sinkhole Collapse of House

Source: U.S. Geological Survey, Water Science for Schools

A change in the local environment affecting the soil mass initiates sinkhole collapses and areas of subsidence. This change is called the "triggering mechanism." Water, either surface or ground water, is generally the most important agent effecting environmental changes that cause subsidence. Triggering mechanisms for subsidence include water level decline, changes in ground-water flow, increased loading, and deterioration (relates to abandoned coal mines).

New sinkholes have been correlated to land-use practices, especially from ground-water pumping and from construction and development practices. Sinkholes can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created. The substantial weight of the new material can trigger an underground collapse of supporting material, thus causing a sinkhole.

Increased numbers of sinkholes can generally be attributed to changing or loading of the earth’s surface with development such as retention ponds, buildings, changes in drainage patterns, heavy traffic, drilling vibrations or a sudden or gradual decline in groundwater levels. In urban areas, all these impacts may occur at the same time, accelerating any sinkhole tendencies. Urban construction, coupled with limestone depths of less than 200 feet, contributes to the development of many of the modern sinkholes.

The built-up sediments that cover buried cavities in the aquifer systems are delicately balanced by ground-water fluid pressure. The water below ground is actually helping to keep the surface soil in place. Ground-water pumping for urban water supply and for irrigation can produce new sinkholes in sinkhole-prone areas. If pumping results in a lowering of ground-water levels, then underground structural failure, and thus, sinkholes, can occur.

Lowering water levels is one of the most significant triggering mechanisms for subsidence in a karst terrain. Water-level decline may occur naturally or be induced by man. Factors leading to a decline in water levels include the pumping of water from wells, localized drainage from construction, dewatering from mining, and periods of drought.

Sinkholes also threaten water and environmental resources by draining streams, lakes, and wetlands, and creating pathways for transmitting surface waters directly into underlying aquifers. Where these pathways are developed, movement of surface contaminants into the underlying aquifer systems can persistently degrade ground-water resources. In some areas, sinkholes are used as storm drains, and because they are a direct link with the underlying aquifer systems it is important that their drainage areas be kept free of contaminants. Conversely, when sinkholes become plugged, they can cause flooding by capturing surface-water flow and can create new wetlands, ponds, and lakes.

(The description of sinkholes presented in this section is based upon information extracted from the FEMA How to Guide Understanding Your Risks (FEMA 386-2), FEMA, August 2001, and other sources from the Geological Survey of Alabama Geological Hazards Program, Southwest Florida Water Management District, and the U.S. Geological Survey Mid-Continent Geographic Science Center).

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5.3.13 Man-Made Hazards Description

Man-made hazards are hazards that originate from human activity. The two categories of man-made hazards are technological hazards and terrorism. Technological hazards are accidental with unintended consequences. They often include the manufacture, transportation, storage and use of hazardous materials. The definition of terrorism has been established by Federal law, as follows: “Terrorism includes the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives.” 28 CFR Section 0.85. In comparison to technological hazards, acts of terrorism are not accidental and the consequences are intentional.

Technological hazards are divided into three categories: fixed facility industrial accident, transportation industrial accident, and the failure of a supervisory control system. For an industrial accident, the hazard will either exist at a fixed location such as a manufacturing plant or storage facility, or while in transport, i.e. in a vehicle that is transporting it from one location to another or while it is moving through a pipeline from one location to another. Supervisory control system failure will affect which ever component within the system it is directing and the extents of the damage possible due to failure are usually easy to predict.

Terrorism includes: the use of weapons of mass destruction – biological, chemical, nuclear, and radiological weapons, explosives, and incendiary devices; arson; armed attacks; agriterrorism; an intentional hazardous materials release; industrial sabotage; and cyber-terrorism. It can be carried out domestically or internationally, by known or unknown assailants, locally or from a distance.

Man-made hazards are very difficult to assess, terrorism more so than technological hazards. Since terrorism involves the human mind and what actions a person may chose to take, the what, where, how and when is largely unpredictable. On the other hand, with technological hazards, since they primarily involve hazardous materials, the assessment of the manufacture, storage, transportation and use of the materials can at least answer to some degree the where, what and how and those answers can aid in the mitigation of some possible technological disasters. For this reason: the scope of man-made hazards addressed by the Mitigation Strategy in this plan is limited to mitigation of fixed location technological hazards involving hazardous materials .

The extent of the effects of a man-made hazard can range from localized to widespread, depending on the type of incident, the mode of application, duration, dynamic/static characteristic and mitigating conditions. A conventional bomb could damage a building in which it was placed or an entire city can be in danger if a hazardous material is released into the water supply. Three noted modes of force to the built environment involved by man-made hazards are: contamination, energy, and failure or denial or service. If a hazard remains for an extended period of time, the damage can be far reaching; however, if the hazard lasts for only a short time, the damage can usually be quickly determined and response can be swift and the disaster contained. A dynamic hazard is more damaging and unpredictable than a static hazard. Mitigating conditions can be deterrents or they can at least lessen the effects of a hazard at a certain location which also affects the extent of a disaster. The following table shows the different possible man-made hazards and their corresponding application mode, hazard duration, extent of effects - static/dynamic, mitigating and exacerbating conditions.

When trying to mitigate man-made hazards, measures must address security, unknown risks and civil liberties; concerns not raised by natural disasters. The events will usually occur in specific locations and mitigation measures can usually aid in the alleviation of man-made disasters. Those specific locations are known as critical facilities. In addition to the facilities usually addressed in vulnerability assessments for natural hazards, the following critical infrastructure is usually assessed: agriculture and food, water, public health, emergency services, defense industrial base, telecommunications, energy, transportation, banking and finance, chemicals and hazardous materials, and postal and shipping. Threats to infrastructure can be carried out by anyone who has the knowledge, opportunity and desire to do harm. They can be anyone from terrorists to upset employees and are therefore largely unidentifiable.

Table 5-11 “Event Profiles for Terrorism and Technological Hazards,” (from the FEMA “How to Guide” for man-made hazards) explains the ways in which man-made hazards can interact with the built environment. As presented in the FEMA Guide, for each type of hazard, the following factors are addressed:


Table 5-11. Event Profiles for Terrorism and Technological Hazards

Man-Made Hazard Application Mode Hazard Duration Extent of Effects; Static/Dynamic Mitigating and Exacerbating Conditions
Conventional Bomb/ Improvised Explosive Device Detonation of explosive device on or near target; delivery via person, vehicle, or projectile. Instantaneous; additional "secondary devices" may be used, lengthening the time duration of the hazard until the attack site is determined to be clear. Extent of damage is determined by type and quantity of explosive. Effects generally static other than cascading consequences, incremental structural failure, etc. Overpressure at a given standoff is inversely proportional to the cube of the distance from the blast; thus, each additional increment of standoff provides progressively more protection. Terrain, forestation, structures, etc. can provide shielding by absorbing and/or deflecting energy and debris. Exacerbating conditions include ease of access to target; lack of barriers/shielding; poor construction; and ease of concealment of device.
Chemical Agent Liquid/aerosol contaminants can be dispersed using sprayers or other aerosol generators; liquids vaporizing from puddles/ containers; or munitions. Chemical agents may pose viable threats for hours to weeks depending on the agent and the conditions in which it exists. Contamination can be carried out of the initial target area by persons, vehicles, water and wind. Chemicals may be corrosive or otherwise damaging over time if not remediated. Air temperature can affect evaporation of aerosols. Ground temperature affects evaporation of liquids. Humidity can enlarge aerosol particles, reducing inhalation hazard. Precipitation can dilute and disperse agents but can spread contamination. Wind can disperse vapors but also cause target area to be dynamic. The micro-meteorological effects of buildings and terrain can alter travel and duration of agents. Shielding in the form of sheltering in place can protect people and property from harmful effects.
Arson/ Incendiary Attack Initiation of fire or explosion on or near target via direct contact or remotely via projectile. Generally minutes to hours. Extent of damage is determined by type and quantity of device/accelerant and materials present at or near target. Effects generally static other than cascading consequences, incremental structural failure, etc. Mitigation factors include built-in fire detection and protection systems and fire-resistive construction techniques. Inadequate security can allow easy access to target, easy concealment of an incendiary device and undetected initiation of a fire. Non-compliance with fire and building codes as well as failure to maintain existing fire protection systems can substantially increase the effectiveness of a fire weapon.
Armed Attack Tactical assault or sniping from remote location. Generally minutes to days. Varies based upon the perpetrators' intent and capabilities. Inadequate security can allow easy access to target, easy concealment of weapons and undetected initiation of an attack.
Biological

Agent

Liquid or solid contaminants can be dispersed using sprayers/aerosol generators or by point or line sources such as munitions, covert deposits and moving sprayers. Biological agents may pose viable threats for hours to years depending on the agent and the conditions in which it exists. Depending on the agent used and the effectiveness with which it is deployed, contamination can be spread via wind and water. Infection can be spread via human or animal vectors. Altitude of release above ground can affect dispersion; sunlight is destructive to many bacteria and viruses; light to moderate wind will disperse agents but higher winds can break up aerosol clouds; the micrometeorological effects of buildings and terrain can influence aerosolization and travel of agents.
Cyber-terrorism Electronic attack using one computer system against another. Minutes to days. Generally no direct effects on built environment. Inadequate security can facilitate access to critical computer systems, allowing them to be used to conduct attacks.
Agriterrorism Direct, generally covert contamination of food supplies or introduction of pests and/or disease agents to crops and livestock. Days to months. Varies by type of incident. Food contamination events may be limited to discrete distribution sites, whereas pests and diseases may spread widely. Generally no effects on built environment. Inadequate security can facilitate adulteration of food and introduction of pests and disease agents to crops and livestock.
Radiological Agent Radioactive contaminants can be dispersed using sprayers/aerosol generators, or by point or line sources such as munitions, covert deposits and moving sprayers. Contaminants may remain hazardous for seconds to years depending on material used. Initial effects will be localized to site of attack; depending on meteorological conditions, subsequent behavior of radioactive contaminants may be dynamic. Duration of exposure, distance from source of radiation, and the amount of shielding between source and target determine exposure to radiation.
Nuclear

Bomb

Detonation of nuclear device underground, at the surface, in the air or at high altitude. Light/heat flash and blast/shock wave last for seconds; nuclear radiation and fallout hazards can persist for years. Electromagnetic pulse from a high altitude detonation lasts for seconds and affects only unprotected electronic systems. Initial light, heat and blast effects of a subsurface, ground or air burst are static and are determined by the device's characteristics and employment; fallout of radioactive contaminants may be dynamic, depending on meteorological conditions. Harmful effects of radiation can be reduced by minimizing the time of exposure. Light, heat and blast energy decrease logarithmically as a function of distance from seat of blast. Terrain, forestation, structures, etc. can provide shielding by absorbing and/or deflecting radiation and radioactive contaminants.
Hazardous Material Release (fixed facility or transportation) Solid, liquid and/or gaseous contaminants may be released from fixed or mobile containers. Hours to days. Chemicals may be corrosive or otherwise damaging over time. Explosion and/or fire may be subsequent. Contamination may be carried out of the incident area by persons, vehicles, water and wind. As with chemical weapons, weather conditions will directly affect how the hazard develops. The micrometeorological effects of buildings and terrain can alter travel and duration of agents. Shielding in the form of sheltering in place can protect people and property from harmful effects. Non-compliance with fire and building codes as well as failure to maintain existing fire protection and containment features can substantially increase the damage from a hazardous materials release.

(The information presented in this section was extracted from the FEMA How to Guide Integrating Manmade Hazards into Mitigation Planning, FEMA 386-7 Version 2.0, FEMA, September 2003).

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5.4 Hazard Profiles

5.4.1 Tornadoes Profile

On February 16, 1995, a devastating F-3 tornado swept 14 miles through the Arab vicinity of Brindley Mountain, killing six people and injuring more than 130 others. According to the Hazard Mitigation Planning Committee (HMPC), Marshall County communities face greatest threats from tornadoes. Hazard exposure, the severity of the risk, and the probability of future occurrences are highest for tornadoes, among all identified hazards in Marshall County. Event records agree with the HMPC’s assessment. As shown on Chart 5-2 below, Marshall County has averaged about one tornado per year over the 56 year period from 1950-2006. (Data by VorTek, LLC, SATT software shows tornadic activity within 20 mile radius of the center of Marshall County, which includes some areas beyond the county limits).


Chart 5-2. Number of Tornadoes Per Year, 1950-2006, Marshall County

Source: VorTek, LLC. SATT 3.0 Site Assessment of Tornado Threat software

During the infamous Palm Sunday Tornado Outbreak of March 27, 2004, an F-2 tornado travelled southwest to northeast across an area just south of the city of Guntersville. According to reports by the National Weather Service in Birmingham, the tornado apparently began along Highway 79 South then cross Big Spring Creek damaging a number of residential structures along Spring Creek Drive. The tornado appeared to weaken but was still strong enough to rip off the top part of the roof to the Marshall Nursing Home and damaging several houses near the entrance to Happy Home. It crossed U. S. Highway 431 near the high school taking out some trees on the side of the mountain and damaging a couple of homes. A total of 103 houses were damaged, 45 of them along Spring Creek Drive and 8 along Highway 79 South. In addition, hail of 0.75 was reported near Arab at 10:55 AM, and 1.75 inches in diameter was reported in Guntersville at 11:15 AM. (Source: NWS, Birmingham).

The most devastating tornado of record is the Dixie Tornado Outbreak of April 24, 1908. At least 34 tornadoes touched down generally east of the Mississippi River from April 23 through April 26, 1908. These tornadoes generally occurred from Texas to Georgia, then northward from Oklahoma to Tennessee. The violent storms killed at least 320 people and injured over a thousand citizens. At least four tornadoes touched down in Alabama during this outbreak of severe weather. These tornadoes were responsible for approximately 48 fatalities and at least 260 injuries. This devastating F4 tornado touched down near Dora in Walker County around 2:40 PM, then continued northeastward until it dissipated near Sylvania in Dekalb County around 4:10 PM. This tornado may have been associated with a family of tornadoes or was one single path. The estimated single tornado damage path would be at least 100 miles long. The width of the damage path varied from around 200 yards to a half mile. Twelve people were killed between Dora and Bergens, which was completely obliterated. Two people were killed in Warrior in Jefferson County, one near Royal in Blount County, and two in Wynnville in Blount Count).


Figure 5-12. Photo of 1908 Tornado
Source: NWS, Birmingham

Fifteen people were killed and at least 150 were injured in Albertville in Marshall County as half the town was destroyed from the 1908 storm outbreak. A nine ton oil tank was reportedly carried around one half of a mile near Albertville. A funnel-shaped cloud swept along the entire path of the storm. The cloud was reported to have had a bounding and whirling motion, and to have swept everything from its path where it touched the ground. A loud, rumbling noise was heard from the cloud, which emitted brilliant lightning. Heavy and damaging hail also fell at points to the north of the storm's path. A train that contained 9 freight cars was overturned and destroyed. There was probably much more damage than documented. Additional loss of life and personal injuries also may have occurred in which no report was received.



Figure 5-13. Photo from March 2002 Tornado

Most recently, on April 10, 2009, an EF-3 tornado caused widespread damage across Marshall County. Three days afterwards, straight winds with velocities up to 75 mph compounded the tornado damages. In all, a total of 23 homes were destroyed and 39 others were heavily damaged. In addition, 39 mobile homes were destroyed with five others heavily damaged. Less than a week after the straight winds, on April 19th, a man and his wife were at home with their grandson when an EF-1 tornado tossed their mobile home upside down over 100 yards. The woman died, the man was critically injured, and the child survived uninjured. Figures 5-13 and 14 show photos from other tornado events in 1985 and 2002. These are just a few of the frequent occurrences of tornadoes common to Marshall County communities.

Figure 5-14. Photos from April 1985 Tornado


As shown on the following charts, Marshall County tornadoes typically occur between March and May of each year with a second season in the late fall. Most tornadoes occur between 2 PM and midnight.

Chart 5-3. Monthly Tornado Frequency, 1950-2006, Marshall County

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software

Chart 5-4. Hourly Tornado Frequency, 1950-2006, Marshall County

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software


Location of Potential Tornadoes

All Marshall County locations and jurisdictions are equally at risk for tornadoes. Paths of tornadoes within a 20-mile radius of the center of Marshall County from 1950-2006 are shown on Map 5-3, and the touchdown locations (1950-2004) are shown on Map 5-4. Although the maps show many of the tornadoes occurring within the Arab and Albertville areas during this period, the entire County is equally susceptible to damage from tornadoes.

Map 5-3. Marshall County Tornado Paths, 1950-2006

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software

Map 5-4. Tornado Locations 1950-2004

The direction of tornadoes is shown in the following Chart 5-5 “Tornado Threat Sectors.” The threat sectors are color coded. Red sectors have had tornadic activity over the 1950-2006 period, and blue sectors have had no activity. The chart indicates most tornados travel from a southwesterly direction.

Chart 5-5. Marshall County Tornado Threat Sectors

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software

Extent and Intensity of Potential Tornadoes

Marshall County tornadoes, on average, tend to be severe and frequent, as shown on the following chart showing the frequency of tornados by intensity over the 1950-2006 period. Also, refer to Maps 5-3 and 5-4, which show the intensity of mapped tornadoes paths and locations. The average intensity of tornadoes since 1950 is F-2. The locations of tornadoes by intensity are random, as shown on these maps.


Chart 5-6. Annual Frequency of Tornado Intensity, Marshall County

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software

Previous Occurrences of Tornadoes

According to the NOAA National Climatic Data Center records of tornadoes in Marshall County beginning in 1957 (see Table E-2 in Appendix E “Hazard Profile Data” for the complete NCDC Storm Events Database for tornadoes), the area had a total of 36 events, averaging 7/10 per year, with 74 injuries, no deaths, and close to $25 million in damages (close to $500K per year). This data differs quite a bit from the National Weather Service (NWS) casualty reports during the same period (refer to Table E-1 in Appendix E). The NWS reported 13 deaths and 344 injuries from 38 tornadoes but does not report damage estimates. This averages to 0.25 deaths per year and 6.6 injuries per year. During a brief nine day period in April of 2009, two tornadoes and a straight line wind event resulted in 23 homes and 40 mobile homes destroyed; 39 homes and five mobile homes heavily damaged; one person critically injured; and one death.

Table 5-12. Annual Summary of Tornado Events, 1957-2008 (NCDC)

Year

Tornadoes

Deaths

Injuries

 Total Damages

1957

2

0

6

 $ 250,000

1958

1

0

1

250,000

1961

1

0

8

250,000

1962

1

0

0

25,000

1964

1

0

0

25,000

1968

1

0

0

250,000

1972

1

0

2

25,000

1973

3

0

3

2,775,000

1974

2

0

1

28,000

1975

1

0

0

25,000

1976

2

0

0

275,000

1978

1

0

0

-

1981

1

0

0

25,000

1982

1

0

1

25,000

1983

2

0

2

2,525,000

1984

1

0

0

25,000

1985

1

0

5

2,500,000

1986

1

0

5

2,500,000

1994

2

0

30

5,500,000

1995

1

0

3

5,010,000

1996

1

0

0

350,000

2001

1

0

7

400,000

2002

1

0

0

1,400,000

2006

3

0

0

110,000

2008

3

0

0

12,000

TOTAL

36

0

74

 $24,560,000

AVERAGE

0.7

0

1.4

 $472,307

Probability of Future Tornado Events

Meteorologists are quick to point out that tornado frequency, intensities, and locations are totally unpredictable. Past records are no guarantee of the probability of future events. If however, past trends would continue, Marshall County can anticipate continued frequent and intense tornadic activity with substantial damages distributed uniformly among all communities. Past trends indicate tornadoes would likely be annual events with infrequent breaks. The average intensity of an annual Marshall County tornado would be around an EF-2, resulting in close to $500K in property damages and causing over six injuries per year and one death every four years. Map 5-5 illustrates the tornado threat levels throughout Alabama, based on historical events. Marshall County lies within a high threat area in North Alabama.


Map 5-5. Alabama Tornado Threat Contours

Source: VorTek, LLC. SATT 3.0 (Site Assessment of Tornado Threat) software

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5.4.2 Severe Storms Profile

According to the Hazard Mitigation Planning Committee (see Appendix D “HMPC Hazard Identification and Ratings”) and surveys of community opinions, severe storms are the second highest natural hazard threat to Marshall County communities. NOAA records confirm these public perceptions. Severe storms bringing high winds, thunderstorms, lightning, and hail are common Marshall County occurrences, and often, tornadoes are associated with these severe storm events.

Several severe and destructive storms passed through Marshall County in mid-April, 2009, as reported by the Birmingham office of the National Weather Service, during the drafting phase of this 2009 plan update. Late in the evening of April 12 and into the early morning hours of the 13th, strong winds developed behind large areas of showers and thunderstorms. Known as a “wake low,” these strong winds developed as the pressure difference grew between this small, but relatively strong area of low pressure in North Alabama and an adjacent area of high pressure present in Georgia. During this particular wake low event, high winds lasted for several hours. Although peak surface winds did not exceed 60 miles per hour, this high wind event caused considerable damage due to its long duration. Numerous trees and power lines were downed, damaging houses and blocking roadways. In Guntersville, several boats were blown ashore and damaged. Just a few days earlier severe storms from an April 10th event spawned a weak tornado which uprooted trees and caused some building damages, and just one week later, an EF-1 tornado accompanying severe storms resulted in one death and one critical injury.

Figure 5-15. April 10, 2009, Severe Storm Radar Imagery

Source: National Weather Service

Location of Potential Severe Storms

All areas of Marshall County have experienced frequent severe storms, including thunderstorms, high winds, heavy precipitation, hail, and lightning and share equal risks for all types of severe storms. The locations of these historical events cannot be mapped.

Extent and Intensity of Potential Severe Storms

The extent of each storm event markedly varies according to storm severity and duration. Storm severity can be measured by the storm characteristics, which may include heavy precipitation, large hail, intense lightning, and high winds. The exact extent of severe storms is not predictable. Severe storms can also result in flooding due to heavy precipitation and wildfires due to lightning and will accompany hurricanes and tornadoes.

Large hail, though very rare, can cause injury or loss of life and major property damages. Normally, however, hail damage is limited to automobiles and minor building damage. Both lightning and high winds have the potential to cause loss of life and considerable property damage. The power of lightning’s electrical charge and intense heat can electrocute on contact, split trees, and ignite fires. High winds are often the cause of power outages and can cause severe damages to buildings and infrastructure by fallen trees and direct wind gusts.

Previous Occurrences of Severe Storms

National Climatic Data Center (NCDC) records indicate frequent annual severe storm occurrences since 1960. There have been over 300 severe storms reported for Marshall County with a frequency of over ten per year. Total damages have been substantial in some cases.

Table 5-13. Annual Summary of Severe Storm Events, 1960-2008 (NCDC)

Year

Type

Number

Deaths

Injuries

 Total Damages

1960

Thunderstorm

1

0

0

$0

1961

Thunderstorm

1

0

0

0

1964

Thunderstorm

1

0

0

0

1965

Thunderstorm

1

0

0

0

1967

Thunderstorm

1

0

0

0

1967

Hail

1

0

0

0

1968

Hail

1

0

0

0

1969

Thunderstorm

1

0

0

0

1973

Thunderstorm

1

0

0

0

1974

Thunderstorm

1

0

0

0

1974

Hail

1

0

0

0

1975

Thunderstorm

3

0

0

0

1975

Hail

2

0

0

0

1977

Thunderstorm

1

0

0

0

1979

Thunderstorm

1

0

0

0

1981

Thunderstorm

2

0

0

0

1982

Thunderstorm

1

0

0

0

1983

Thunderstorm

2

0

0

0

1983

Hail

1

0

0

0

1984

Thunderstorm

2

0

0

0

1984

Hail

1

0

0

0

1985

Thunderstorm

11

0

0

0

1986

Thunderstorm

4

0

0

0

1986

Hail

1

0

0

0

1987

Thunderstorm

1

0

0

0

1988

Thunderstorm

3

0

0

0

1989

Thunderstorm

3

0

0

0

1989

Hail

4

0

0

0

1990

Thunderstorm

3

0

0

0

1990

Hail

1

0

0

0

1991

Thunderstorm

3

0

0

0

1992

Thunderstorm

4

0

0

0

1992

Hail

2

0

0

0

1993

Thunderstorm

1

0

0

0

1994

Thunderstorm

5

0

0

565,000

1994

Hail

3

0

0

5,000

1994

Precipitation

1

0

0

0

1994

Lightning

3

0

0

60,000

1995

Thunderstorm

6

0

0

51,000

1995

Hail

1

0

0

0

1995

Lightning

4

0

1

63,000

1996

Thunderstorm

9

0

0

751,000

1996

Hail

3

0

0

51,000

1996

Lightning

2

0

0

30,000

1997

Thunderstorm

8

0

0

73,000

1997

Hail

4

0

0

58,000

1997

Precipitation

1

0

0

50,000

1997

Lightning

1

0

0

7,000

1998

Thunderstorm

12

0

0

202,000

1998

Hail

10

0

0

193,000

1998

Lightning

1

0

0

30,000

1999

Thunderstorm

9

0

0

26,000

1999

Hail

3

0

0

3,000

1999

Precipitation

1

0

1

0

1999

Lightning

2

0

0

17,000

2000

Thunderstorm

4

0

0

144,000

2000

Hail

3

0

0

4,000

2001

Thunderstorm

4

0

0

14,000

2001

Hail

3

0

0

2,000

2002

Thunderstorm

5

0

0

213,000

2002

Hail

4

0

0

0

2002

Lightning

1

0

0

25,000

2003

Thunderstorm

11

0

0

2,000

2003

Hail

18

0

0

0

2004

Thunderstorm

15

0

3

2,505,000

2004

Hail

2

0

0

0

2005

Thunderstorm

7

0

0

0

2005

Hail

9

0

0

0

2006

Thunderstorm

13

0

0

27,000

2006

Hail

16

0

0

35,000

2006

Lightning

1

0

0

2,000

2007

Thunderstorm

10

0

0

0

2007

Hail

1

0

0

0

2008

Thunderstorm

11

0

0

16,000

2008

Hail

7

0

0

0

TOTAL

 

302

0

5

*$5,224,000

Annual Average

 

10.4

0

0.2

*$180,138

*includes damages for Marshall and other Alabama counties

Source: National Climatic Data Center

Probability of Future Severe Storm Events

Frequent annual events are certain. Past trends show annual occurrences of thunderstorms, hail, and lightning, which are likely to continue throughout all Marshall County jurisdictions. High winds are less frequent, and large, damaging hail is rare.

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5.4.3 Floods Profile

On December 9, 2004, a rainfall of several inches resulted in many road closures due to flash flooding throughout Marshall County. This is a typical flash flood event, a recurring problem throughout the County.

According to the Hazard Mitigation Planning Committee (see Appendix D “HMPC Hazard Identification and Ratings”) and surveys of community opinions, floods are a moderate concern to Marshall County communities. NOAA records confirm these public perceptions, and many other localized flooding events have been reported by local newspapers. These local news archives show that occasional storm bursts exceeding four inches of rain in a short period of time have forced evacuations of home, road and bridge closings, and flooding of buildings.

Location of Potential Floods

According to the Flood Insurance Rate Maps (FIRM’s) of the National Flood Insurance Program (NFIP), Marshall County does not have extensive flood plains. Map 5-6 “Flood Zones” shows most flood zones are limited to rural locations in unincorporated areas of the County. The major concern is not riverine flooding of Lake Guntersville, the Tennessee River, and their tributaries; rather the concern is with more localized flash flooding of roads and bridges following heavy rain falls. These flash flood conditions are common throughout the County.

Map 5-6. Flood Zones


Extent and Intensity of Potential Floods

The extent of each flood varies according to the amount of rainfall, the rate of storm water flow, and the capacity of the receiving channel to discharge flood waters. Almost all of Marshall County flows through a system of tributaries and drainage ways to Lake Guntersville and the Tennessee River. The Guntersville Dam on the Tennessee River is a control for Guntersville Lake capacity and is effective in preventing damages from major rainfall events. Consequently, most damaging events are as a direct result of inadequate local drainage systems unable to handle excessive rainfalls. This often results in flash flooding. These flash flood events can vary quite a bit in severity depending on the rate and amount of precipitation and local drainage conditions. Generally, however, Marshall County has moderate risk of damages due to floods. Extensive flood zones are primarily confined to rural locations below Guntersville Dam on the Tennessee River, along the northern county limit, and southwest of Lake Guntersville, where property damages from a 100-year flood would be minimal.

Previous Occurrences of Floods

National Climatic Data Center (NCDC) records (see Table E-9 in Appendix E for the complete NCDC listing) indicate frequent flooding over the period since 1997. There have been 21 floods reported for Marshall County with a frequency of almost two per year, as shown in Table 5-14 below. Total recorded damages have been minor, according to the NCDC estimates. The NCDC records and estimates, however, conflict with local news reports. See Table E-10 in Appendix E for select local newspaper accounts of 13 flooding events over a 35 year period, resulting in significant damages to buildings, roads, and bridges and evacuations of homes. Apparently, the impacts of flooding in Marshall County are much worse than the NCDC records indicate.

Table 5-14. Annual Summary of Flood Events, 1997-2008 (NCDC)

Year

Floods

Deaths

Injuries

Total Damage

1997

3

0

0

$64,000

1998

1

0

0

55,000

1999

1

0

0

8,000

2000

1

0

0

10,000

2001

2

0

4

103,000

2003

5

0

0

250,000

2004

6

0

0

0

2008

2

0

0

27,000

TOTAL

21

0

4

$517,000

AVERAGE

1.9

0

0.4

$47,000

Source: National Climatic Data Center

Probability of Future Flood Events

Past trends indicate regular occurrences of heavy rainfalls should continue to create conditions of flash flooding in throughout Marshall County. According to the HMPC hazard ratings of floods, the City of Arab rated the probability for flooding in its community as very high; all others were low to medium probability. The 100 and 500-year flood events should be unlikely from year to year, but when these infrequent events take place, damages should not be substantial and widespread.

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5.4.4 Winter Storms/Freezes Profile

Although winter storms in Alabama are not as common as in more northern regions of the U.S., the most frequent Alabama occurrences are in the higher elevations of northern Alabama, such as the Sand Mountain communities of Marshall County. Still, such storms are usually relatively mild, characterized by an occasional dusting of snow or short freezing rain falls. Rarely do snowfalls exceed two inches or freezes disrupt road travel for long periods. On average, the county receives 1.2 inches of snowfall annually with about one event per year. When the occasional snow storm or severe freeze does occur, however, major transportation disruptions and power outages may be experienced. This is largely due to local inexperience in coping with such infrequent occurrences. Consequently, the risks associated with this type of weather are largely a direct correlation to the community’s ability to handle the storm. These risks include loss of life due to cold, loss of electricity for extended periods of time, agricultural damage, and road hazards. Fallen trees and limbs and heavy snow loads can cause roof collapses and downed power and communications lines. Heavy snowfalls over two inches and long-lasting freezes are more infrequent but create higher risks. Disruptions can last for several days following these extreme winter storm conditions.

Winter temperatures in Marshall County are generally moderate, with average temperature of 43.8° F and average minimums at 33.0° F. Extreme cold temperatures are rare but do occur. These rare temperature lows could result in burst plumbing in homes and occasional deaths due to lack of sufficient heating or exposure. The lowest recorded temperature of -11° F occurred in 1985.

Table 5-15. Winter Weather Observations

 Item

Observation

Average Winter Temperature

43.8° F

Average Winter Minimum Temperature

33.0° F

Lowest Temperature (January 21, 1985)

-11° F

Average Season Snowfall

1.9 inches

Largest Snowfall (January 7, 1988)

9.1 inches

Source: SE Regional Climate Center

Location of Potential Winter Storms/Freezes

Marshall County and its participating jurisdictions are equally likely to experience winter storms/freezes, which may include snow, freezing rains, and extreme temperature lows. All areas of the county are equally exposed to these types of weather events with somewhat colder temperatures and snowfall frequency in the higher elevations.

Extent and Intensity of Potential Winter Storms/Freezes

On average, Marshall County experiences annual disruptions and some damages due to severe winter storms/freezes. The average snowfall is 1.2 inches yearly, but some events have produced major disruptions and damages. Winter temperatures on average are above freezing, but occasional freezes do occur. The Hazard Mitigation Planning Committee (HMPC) (see Appendix D “HMPC Hazard Identification and Ratings.”) rated the extent of winter storms/freezes as moderately high.

Previous Occurrences of Winter Storms/Freezes

Table 5-16 “Winter Storm Damages” provides a summary of the available historical data since 1993 for winter weather events in Marshall County. There have been 15 reported winter storm events since 1993 according to the National Climatic Data Center. (Refer to Table E-12 “Marshall County Snow and Ice Events, 1993-2008” in Appendix E). Prior to 1993 no official records are available from the NCDC, but local news reports of some of the winter storms/freezes are summarized in Table 5-18, which provides an additional listing of all the winter weather events since 1960. Table 5-17 reports extreme temperature lows. (Refer to Table E-12 “Marshall County Extreme Cold Events, 1996-2008” in Appendix E). Some of the most significant winter storm events over the last 49 years are described below.

The most recent recorded snow event is a light snowfall on December 1, 2008, with accumulations of one-half to one inch in parts of Marshall County.

The December 23-25, 1998, winter storm brought a mixture of freezing rain, sleet, and rain to the northern half of Alabama. Marshall County was especially hard hit. The precipitation began around 2 am and lasted until early afternoon on the 24th, with temperatures at or below freezing for the majority of the event. Rain precipitation ranged from one to three inches, and ice accumulations of one half to one inch were common. Numerous trees were down. Significant power outages were not restored in many locations until the 26th or 27th. The National Guard was activated o help with the cleanup duties. Numerous roads were closed during the event which included Interstate 65 and 565 in the Huntsville area. Numerous multiple vehicle and single automobile accidents occurred due to the icy road conditions. These accidents resulted in at least five fatalities and numerous minor injuries in northern Alabama.

On February 4, 1998, a winter storm brought two to six inches of snowfall over the northeast region of the state. This storm resulted in vehicle accidents due to slick roads, and downed power lines.

Record low temperatures affected much of North Alabama, when unusually cold temperatures of 15 to 22 degrees over the March 7-10, 1996, period caused major crop damages.

Between February 1 and 3, 1996, a winter storm brought freezing precipitation to North Alabama. Freezing rain followed by light snow brought halted traffic, and ice accumulations downed trees, resulting in widespread power outages. A number of commercial chicken houses collapsed under the weight of ice and snow. Marshall County school systems remained closed for a week. Freezing temperatures dipped below 10 degrees. Another winter storm occurred just one month earlier on January 6, 1996.

The most damaging winter storm in Alabama history was in March 1993 with damages totaling $5.0 billion dollars. This event is commonly referred to as the “Blizzard of 1993,” which had severe impacts throughout the eastern U.S., affecting 26 states and parts of Canada. The storm began on Friday March 12, 1993, and lasted through mid-day Saturday, March 13, 1993. By mid-day Saturday snow had accumulated to 6 to 12 inches over North Alabama. An estimated 400,000 homes were without electricity, and many remained so for several days. Compounding the snow and power problems, temperatures fell well into the single digits and teens across much of the state Saturday night. There were at least 14 deaths associated with the storm. The entire state was declared a Federal Disaster Area.

The largest snowfall recorded in Marshall County occurred on January 7, 1988 at 9.1 inches, which accompanied an ice storm that affected the northern two thirds of Alabama. Ice accumulation was nearly an inch in some locations.

Additional winter storm events since 1960 and prior to 1988 are described in Table 5-16 below.


Table 5-16. Winter Storm Damages

Year

Winter Storm

Deaths

Injuries

Total Damages

1993

1

4

0

$5,000,000,000

1995

2

0

0

0

1996

3

0

0

1,208,000

1997

2

0

0

64,000

1998

2

0

0

14,427,000

1999

1

0

0

0

2000

1

0

0

75,000

2001

1

0

0

0

2004

1

0

0

0

2008

1

0

0

0

TOTAL

15

*

*

*

Annual Average

0.9

*Multiple counties affected; cannot compute averages for Marshall County

Source: National Climatic Data Center

Table 5-17. Extreme Cold Events and Damages

Year

Extreme Cold

Deaths

Injuries

Total Damages

1996

2

1

0

$52,000,000*

*Multiple counties affected

Source: National Climatic Data Center

Table 5-18. Select Local News Reports of Winter Storms, 1960-1987

Date

Source

Comment

3/1/1960

Arab Tribune

Called out National Guard, Civil Defense, Highway Patrol, Electric and telephone crews from across Southeast. Parts of Alabama without power for 3 weeks.

3/17/1960

Arab Tribune

5 inches of snow

2/2/1961

Arab Tribune

700 without power in Arab area due to ice storm.

1/9/1962

Arab Tribune

More than 5inches of snow fell in parts of Marshall County.

12/18/1962

Arab Tribune

-4° F.

1/12/1963

Arab Tribune

Sub-freezing weather, ice then snow, closed Highway 231

12/22/1963

Arab Tribune

Snow turns to ice, closes roads, power out

12/31/1963

Arab Tribune

10.5 inches of snow, some drifts 18-20 inches

11/2/1966

Arab Tribune

3 inches of snow

1/11/1968

Arab Tribune

5 inches of snow, schools closed

2/15/1968

Arab Tribune

Major power outages in Marshall County

2/28/1968

The Advertiser-Gleam

2-5 inches of snow, schools closed, power outages

2/20/1969

Arab Tribune

Ice covers Brindlee Mountain topped by snow, power outages.

1/6/1970

Arab Tribune

3 inches of snow on Brindlee Mountain

1/14/1970

Arab Tribune

Ice, snow and fog cause travel problems on Brindlee Mountain for several days.

1/20/1970

Arab Tribune

Ice and snow closed schools and some roads.

2/2/1970

Arab Tribune

6° F at Brindlee Mountain

1/3/1977

Arab Tribune

Ice and snow closed roads in Arab area.

1/10/1977

Arab Tribune

6° F low and 27° F high for one week causes energy shortage in both gas and electricity.

1/9/1978

Arab Tribune

1.5 inches of snow fell on Brindlee Mountain, schools closed

2/18/1979

Arab Tribune

Ice storm paralyzed Arab and Brindlee Moutain. Power outage.

1/14/1982

Arab Tribune

4.5 inches of snow fell on Marshall County, roads closed

1/13/1983

Arab Tribune

Ice and snow close roads and schools in Marshall County.

1/2/1984

Arab Tribune

Hard freeze (0° F) caused broken water lines at Water Works storage tanks causing water shortage in some areas.

1/19/1985

Arab Tribune

1-3 inches of snow in Brindlee Mountain area.

1/19/1985

Arab Tribune

-11° F with 1 to 3 inches of snow in Brindlee Mountain area.

2/12/1985

Arab Tribune

2-4 inches of snow fell in Brindlee Mountain area, schools and roads closed.

1/27/1986

Arab Tribune

0° F, 2 inches of snow

1/21/1987

Arab Tribune

3 inches of snow in Arab, schools closed.

4/3/1987

Arab Tribune

5 inches of snow

Probability of Future Winter Storm/Freeze Events

Winter storms/freezes should continue to affect Marshall County on an annual basis to some extent. More severe events with heavy snowfalls exceeding two inches, long lasting freezes, and extreme lows should be more infrequent at a rate of one per three to five years. Certainly, however, the historical records cannot determine future outcomes; frequency of these events is totally unpredictable. The Hazard Mitigation Planning Committee (see Appendix D) rated the probability of future occurrences at moderately low. The risks associated with the average annual hazard are slight, but the more infrequent but severe winter storms/freezes have potentially severe risks. These severe winter events can cause major transportation disruptions, lengthy power outages, substantial property damages, and some loss of life. Map 5-7, which follows, shows the higher relative frequency of winter storms in North Alabama over the 1993-2006 period.

Map 5-7. Alabama Winter Storm Frequency (1993-2006)

Source: 2007 Alabama State Plan

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5.4.5 Hurricanes Profile

Five in five years – that is the number of Federal disaster declarations for hurricanes that have included Marshall County over the 2004 to 2009 period. Beginning with Hurricane Ivan on September 15, 2004 (declaration #1549), other hurricane declarations have included Dennis on July 10, 2005 (#1593), Katrina on August 29, 2005 (#1605 and #3237), Gustav on August 30, 2008 (#3292 and #1789), and Ike on September 26, 2008 (#1797). Although Marshall County is approximately 300 miles inland from the Gulf Coast, it is not immune to the damaging effects of hurricanes.

Location of Potential Hurricanes

All Marshall County locations and jurisdictions generally share equal risk for hurricanes. According to a probabilistic model of hurricanes using FEMA’s HAZUS-MH hurricane module, peak wind gusts from a 100-year probability hurricane event, approach 67 mph, decreasing slightly in the northern areas of Marshall County (see Map 5-8 “100-Year Hurricane Wind Speeds”). In this 100-year event scenario, the storm track lies immediately to the west of Marshall County, traveling to the northeast. This is similar to the Hurricane Opal track of October 1995 and the Hurricane Ivan track of September 2004.

Map 5-8. 100-Year Hurricane Wind Speeds

Extent and Intensity of Potential Hurricanes

Inland hurricanes will dissipate by the time they reach Marshall County, which is located over 300 miles from the closest Gulf Coast landfall location. Should the path pass through or very near Marshall County, the hurricane would be downgraded to a tropical depression with thunderstorms and maximum sustained winds of 38 mph or less. If rated as an inland tropical storm, maximum sustained winds could as high as 73 mph. High wind gusts, as demonstrated through the HAZUS-MH 100-year scenario, of up to 67 mph can cause trees, signs, and power lines to topple, damaging buildings and causing sustained power outages. Some deaths may occur as a result of falling trees and electrocution from downed power lines.

Tropical storms and depressions often bring torrential rains and flooding, which may last for days after the storm has passed. The dissipated strength of the inland storm does not necessarily affect the amount of rainfall and resultant flood levels. A weak tropical storm or depression moving slowly or lingering can cause more damage due to flooding than a fast moving hurricane.

Tornadoes may also occur but not always - some produce none, while others spawn numerous ones. According to hurricane records, half produce one or more tornadoes with capabilities to compound wind damages. A tornado normally occurs within 12 hours of landfall and during daylight hours. This timeframe is within reach of Marshall County. Normally, a tornado watch will usually follow the projected inland path of a hurricane.

Previous Occurrences of Hurricanes

One of Alabama’s most significant inland hurricane events of record, Hurricane Opal, came ashore in the Florida Panhandle on October 4, 1995, and moved across the state of Alabama to its northeast corner of Alabama, having direct impacts on Marshall County. Wind damage was extensive and no Alabama county was spared some effect, with many trees, signs, and power lines downed. At its worst, 2.6 million people in Alabama were without electricity, some for over a week. The center of the storm moved just west of the City of Montgomery, near the City of Talladega, and near Fort Payne before exiting the state. Wind speeds varied across the state; at nearby Huntsville, winds were recorded at 55 mph, and to the southeast in Etowah County, two people were killed from a toppled tree. Heavy rains caused streams to swell to bank full and beyond. Water damage occurred to structures in many locations where wind or falling trees damaged roofs.


Map 5-9. Hurricane Opal Track

Source: National Hurricane Center

Ivan made landfall around 1:00 AM CST near Gulf Shores, Alabama on September 16, 2004. By 10 PM, the storm had passed through Marshall County as a tropical depression with sustained winds of 35 mph and gusts of up to 60 mph. The following maps show the path and strength of Ivan as it passed through Marshall County.

Map 5-10. Hurricane Ivan Track

Source: National Hurricane Center

Map 5-11. Hurricane Ivan Alabama Path

Source: National Weather Service, Birmingham

Map 5-12. Hurricane Ivan Alabama Peak Wind Gusts

Source: National Weather Service, Birmingham

Prior to Hurricane Ivan in 2004, many hurricanes have affected Marshall County. The paths of these storms since 1851 are shown on Map 5-13. “Hurricane Paths, 1851-2004,” which shows all areas of Marshall County equally affected. Other hurricanes affecting Marshall County since 2004 include the remnants of Dennis on July 10, 2005, and Katrina on August 29, 2005.

Map 5-13. Hurricane Paths, 1851-2004

Probability of Future Hurricane Events

As is the case with most natural hazards, past records are no guarantee of the probability of future hurricane events affecting Marshall County. Given its inland location within about 300 miles of the Gulf Coast, however, Marshall County can continue to expect the remnants of frequent Gulf Coast hurricanes and occasional direct impacts of tropical depressions. Hurricane path records since 1851 show the likelihood of continued direct paths through or nearby Marshall County. The county’s location within ten hours of a Gulf Coast hurricane landfall would cause the hurricanes to dissipate to tropical depression status. The probable impacts of tropical depressions directly passing through or near Marshall County would be damages resulting from high wind gusts above 65 mph, heavy rainfall causing localized flooding of streams and drainage ways, and possible tornadoes.

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5.4.6 Droughts/Heat Waves Profile

The biggest weather story of 2007 for Marshall County and Central Alabama was the historic drought that broke all records for the driest year. With drought conditions carrying over from 2006, by late spring of 2007, the drought moved up to a D4 Exceptional Drought intensity, the highest intensity, which is characterized by widespread crop and pasture losses, wildfires, and severe shortages of water resources in reservoirs, streams, and wells. The 2007 drought was not limited to Marshall County and Central Alabama; it became widespread, affecting most of the southeastern U.S. Drought conditions persisted throughout the remainder of the year and through the end of 2008. These exceptional conditions affected every segment of the population: crop yields were greatly below normal; livestock suffered as ponds and wells dried up; forestry weakened; trees became more brittle and vulnerable to snapping during severe weather events; lake levels fell with many boats and docks in Central Alabama standing on dry land and marinas closing; major shipping routes throughout Alabama became almost impassable; and lawns and gardens dried up as many communities imposed strict water restrictions. Drought conditions persisted throughout 2008 until being lifted on December 16. The weather story of year 2007 was heightened by one of the warmest years of record in Central Alabama.

Location of Potential Droughts/Heat Waves

Droughts and heat waves occur countywide, affecting all Marshall County jurisdictions. Some areas may be more susceptible to the effects of drought such as agricultural areas and areas with vulnerable water supplies.


Extent and Intensity of Potential Droughts/Heat Waves

The drought event that occurred during 2007 was the driest time in recorded history, which dates back over a century. The National Weather Service in Huntsville indicated that Marshall County was in a mild to moderate drought as early as June 2006 that continued to worsen through 2007. It ranks as the driest calendar year in history with only 16.49 inches of rainfall. The second driest year occurred in 1902. On June 5, 2007, Marshall County was included in a D4 exceptional drought classification, which is the worst intensity of the five-category system used by the U.S. Drought Monitor. During the spring of 2008 there was some needed rain when the drought status was downgraded and lifted by year’s end.

Previous Occurrences of Potential Droughts/Heat Waves

According to the National Climatic Data Center (NCDC) records, there have been 17 drought occurrences that have occurred during 2007 and 2008. Prior to 2007 there was no information available in the NCDC database for Marshall County. There are four instances of droughts/heat waves recorded in local news reports. These events are recorded in Table E-17 in Appendix E “Hazard Profile Data”. According to the NCDC, there have been reports of three extreme heat events. These are provided in Table E-16 “Marshall County Extreme Heat Events” in Appendix E. Also included in Appendix E are summaries of five news articles about the drought events that occurred in 2006 through 2008.

Table 5-19. Drought and Damages Table

Year

Drought

Deaths

Injuries

Total Damages

2007

10

0

0

$0

2008

7

0

0

$0

TOTAL  

17

0

0

$0

Source: National Climatic Data Center

Table 5-20. Extreme Heat and Damages

Year

Extreme Heat

Deaths

Injuries

Total Damages

1996

1

0

0

$0

2000

1

1

0

$0

2007

1

0

0

$0

TOTAL

3

1

0

$0

Source: National Climatic Data Center

Probability of Future Drought/Heat Wave Events

Marshall County is susceptible to drought and heat waves. Although there is not a great deal of historical record of drought conditions, it can occur. The Hazard Mitigation Planning Committee (HMPC) ranked the probability of drought and heat waves occurring much higher than in the same exercise during the 2004 plan development. The HMPC now indicates that drought and heat wave have a medium likelihood of occurrence. They also indicate that they believe the extent of the hazard is moderately high in severity. (See Appendix D “HMPC Hazard Identification and Ratings”). This change in view reflects the influence of the recent drought/heat wave events since the 2004 plan.

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5.4.7 Wildfires Profile

The two primary categories of wildfires experienced in Marshall County are wild land fires and interface fires. Wild land fires are fueled exclusively by natural vegetation. Marshall County has vast forested lands, grass lands, and brush to fuel wildfires. Map 5-14 “Marshall County Forest Fuels” shows the extensive coverage of forest fuels throughout the county, as well as developed urban areas in close proximity to the forest fuels. Interface fires are fueled by both vegetation and the built up environment. Due to the current growth in Marshall County, many families are pushing urbanization into rural landscapes. This is known as the wild land-urban interface. With this urban-to-rural movement comes the increased risk of man-made wildfires.

A major problem in relation to wildfires is non-permitted burns. These burns tend to rage out of control, leading to damaging fires. Without the practice of prescribed burns, thinning, mowing and the use of herbicides, vegetation that will spread fires can proliferate causing more of a threat with the additional fuel sources for wildfires. The practice of prescribed burns not only helps reduce the fuels available for wildfires, but also aids in the development of certain habitats and the regeneration of certain species.

Location of Potential Wildfires

Primarily rural areas of unincorporated Marshall County are susceptible to wildfires; however, wildfires can occur in any area where there is the proper fuel, topography, and weather mix. The vulnerable wild land-urban interface makes all cities and towns equally susceptible. Map 5-15 “Marshall County Wildfire Risk,” denotes areas throughout the county at various risk levels for wildfires.

Extent and Intensity of Potential Wildfires

Marshall County has multiple fuel sources and is prone to drought and thunderstorms which increase the potential severity of wildfires significantly. The county has an abundant fuel source with 173,800 acres of forestland. Weather conditions, given the high frequency of severe storms with lightning and periodic severe drought conditions, can exacerbate wildfires.

Another factor that has direct impact on wildfire formation and increase the risk for wildfires in Marshall County is topography. Topography can have a powerful influence on wildfire behavior. Slope, canyons, gulches, and hollows can greatly increase the rate of spread and hamper access. These slopes lend themselves to rapid spreading fires due to their angle. The greater the slope, the faster the flames move and the longer the flames. Wildfires can reach into overhanging canopies, allowing spread not only through the lower areas of the forest, but the ability to jump to other trees. According to the local Alabama Forestry Commission office, the terrain is extremely rough over parts of Marshall County, making suppression efforts extremely difficult and time consuming.

The degree of exposure of properties at the wild land-urban interface also affects the extent of wildfires in Marshall County, especially at the edge of developed areas of cities and town. High risk properties located within these interface areas have the greatest potential for property damages and threats to life.

Finally, firefighting resources can affect the severity of wildfires. Rural fire departments are almost exclusively made up of volunteers and usually have limited resources that are stretched during periods when numerous fires occur. These limited firefighting resources can compound the risk and extent of wildfire damages.

Past Occurrences of Wildfires

According to the Alabama Forestry Commission, Marshall County averaged 17.2 fires per year with an average of 284.2 acres burned per year, based on figures from the ten-year period from 1999 through 2008. The county ranks 56 among 67 Alabama counties for number of fires and 49th for acres burned. Of the approximately 173,800 acres of forestland, the 284.2 acres burned per year accounts for a relatively small proportion of less than 0.2% of the total forestland. Most of the reported fires occurred during the months of February, March and April, which are most susceptible to fires.

The relatively low rankings of Marshall County wildfire extent and frequency in comparison to other Alabama counties may be credited to the local fire departments ability to respond to the fires and their effectiveness in containing the blaze. The number of fires has decreased over the last twenty years due to public education and the increase in the number and effectiveness of volunteer fire departments throughout the county. Maps on the following pages show the broad distribution of fire fighting resources throughout the county.

Map 5-16 “Marshall County Fire Observations” shows the location of wildfire occurrences over the 2000 to January 2009 period. These are generally random locations. Map 5-17 “Marshall County Fires per 1,000 Acres” shows areas at various levels of wildfire occurrences from low to extreme. These wildlife occurrence areas generally coincide with areas denoted as medium to high risk areas on Map 5-15 “Marshall County Wildfire Risk.”

The weather is a natural contributor to wildfire occurrences. Extreme dry weather creates the perfect conditions for woodlands ready to spread fire rapidly. Droughts increase the inflammability of vegetation and pose greater difficulty in suppressing fires. In the midst of the 2006-2008 drought, in March 2007, a very dry month, there were approximately 1,000 acres a day burned in the State of Alabama. In addition to drought, lightning can strike woodlands setting them on fire and trees that had been downed through severe weather events can add to the vegetative fuels to make timber for fires.

During the height of the drought in 2007, Marshall County had two relatively large wildfires. One occurred on Bishop Mountain on May 26, 2007 and the other occurred on Gunter Mountain on October 7, 2007. The fire on Bishop Mountain burned approximately 100 acres, and the fire on Gunter Mountain burned approximately 75 acres. These two fires burned a combined 175 acres, which is nearly 62% of the yearly average of 284.2 acres. The severe drought conditions contributed to the size of these two fires.

Probability of Future Wildfire Events

The average of 17.2 fires a year over the ten year period ending in 2008 has increased only slightly as result of recent drought conditions, but has generally held steady within a range of approximately 14 to 20 fires per year. Over the five year period from 2004 to 2008, the number of fires per year increased to 20, but the 2008 incidence was 14. Unless there are major changes in the weather or the urban-wild land interface, the probability, based on recent trends should remain close to 17 fires per year.

Based on historical information, Marshall County can expect an average of sixteen significant wildfires per year that damage or destroy an average of 204 acres. Although one can extract data and probability of occurrence from historical information, the risk of a wild fire occurring and the location of damage appear to be random.


Map 5-14. Marshall County Forest Fuels

Map 5-15. Marshall County Wildfire Risk

Map 5-16. Marshall County Fire Observations

Map 5-17. Marshall County Fires per 1,000 Acres


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5.4.8 Dam/Levee Failures Profile

Marshall County has five dams and one levee within its jurisdiction. The principal TVA dam, Guntersville Dam, creates the Guntersville Reservoir with over 900 miles of shoreline within the County. Nickajack Dam located 70 miles northeast of Guntersville in Tennessee could also have dam failure impacts within Marshall County. Dam/levee failures are rare occurrences but the potential downstream damages could be significant due to the force and surge of huge volumes of water.

Alabama is one of only two states in the U.S. that currently has no statewide dam safety and inspection program. There have been numerous attempts, beginning in 2002, to pass dam safety legislation, with the last failed effort introduced in the Alabama legislature in February 2008 by HB 454, “Alabama Dam Inventory and Classification Act.” This bill would have established the Alabama Dam Security and Safety Program within the Alabama Department of Economic and Community Affairs (ADECA) Office of Water Resources. This is the agency which also administers the National Flood Insurance Program. Once established, the program would provide for a full inventory of dams throughout the State and help benefit public safety and emergency response operations in the event of a natural disaster. The new program would also provide for the permitting and certification of dams that meet specified criteria designed to reduce dam failure.

Location of Potential Dams/Levee Failures

Figure 5-16. Guntersville Dam Plan Details

As shown on Map 5-18 “Dams/Levees,” there are five dams and one levee located within the County. The Guntersville Dam is the largest of the five and is also considered a high hazard dam; this indicates that its failure will likely cause loss of human life. This classification is not an indicator of the dam’s soundness and quality of construction but rather the potential damage a failure would cause. Marshall County could also suffer damage from the failure of the Nickajack Dam located outside of the County. Both of these dams are monitored by the Tennessee Valley Authority (TVA) and have emergency action plans. The other four dams are earthen, and two are located on private property. These two dams would not cause significant damage if failure occurred. The other two earthen dams could cause damage to surrounding properties if they failed. One is located near Grant in the northern portion of the County. It helps form Woodall Lake and is maintained by the Marshall County Commission. The other is within the City of Arab. It is located at Pine Lake Village and is maintained by the City.

Guntersville Dam is the largest dam within the County. It stretches across the Tennessee River to create the Guntersville Reservoir. The Guntersville Dam was completed in 1939; it is 94 feet high and stretches 3,979 feet across the river. The dam provides almost 890 miles of shoreline and 67,900 acres of water surface. This shoreline provides most of the County’s recreation including 3 State parks, 3 County parks, 8 municipal parks, 4 State wildlife centers, 30 public access areas and 23 commercial recreation areas. The generating capacity of Guntersville Dam is 140,400 kilowatts of electricity.

Figure 5-17. Photo of Guntersville Dam

A failure of Guntersville Dam would cause flood inundation from Union Grove to along the Madison/Marshall County line along the Tennessee River. Impacts would also occur along the tributaries of the river. The failure of the dam would impact the affected area at a 100 and 500 year flood level.

Figure 5-18. Nickajack Dam Plan Details

Located outside of the County, Nickajack Dam also would cause substantial property damage if failure occurred. It is located upstream in Marion County, Tennessee. Nickajack Dam was completed n 1967. It is 81 feet high and stretches 3,767 feet across the Tennessee River. It is the sixth step in the set of locks and dams that carry barges up and down the river. The 110 by 600 foot lock now in operation can lift as many as nine barges at one time. During construction, the foundation for another 800-foot lock was also built so that it can be completed when the need arises. The Nickajack Dam provides 179 miles of shoreline and 10,370 acres of water surface.

If the Nickajack Dam failed, the shorelines of Guntersville Reservoir would be impacted from a sudden flood of water. In a failure during a non-flood condition, the limit of downstream impact would occur along the Jackson/Marshall County line south of Deal Creek. Much of the flooding would occur along the tributaries of the Tennessee River and Guntersville Lake.

One levee is located within Marshall County. The levee is located in the City of Guntersville along the Guntersville Reservoir. It is in the downtown area and is utilized as a walking trail. The City maintains it, and the TVA monitors the water level.

Extent and Intensity of Potential Dam/Levee Failures

Marshall County could experience damages from the two TVA dams along the Tennessee River (Guntersville and Nickajack Dams). The 100 and 500-year frequency dam inundation areas identified by TVA are shown on Map 5-19. “Dam Failure Inundation Areas.” Inundation studies for smaller dams and levees have not been completed.

The Guntersville Reservoir serves as a flood control impoundment with water surface elevations controlled by the dam. As a result, areas around Lake Guntersville and within the City of Guntersville have minimal areas of special flood hazard identified. Downstream of Guntersville Dam, the 500 year inundation extents would be similar to the 500 year flood heights and have equivalent impacts. In the event of major failure of Nickajack Dam, 100 and 500 year flood inundations would be limited to the shoreline of Lake Guntersville. Travel distance from Nickajack Dam is approximately 70 miles. This long distance allows for the timing of the peak flow to be forecasted. Consequently, emergency preparedness actions could allow for evacuation and protection of vulnerable properties. Most affected areas are rural and outside of incorporated jurisdictions.

The failure of two earthen dams on public property could cause downstream property damages. These public dams include Woodall Lake Dam northwest of the Town of Grant and maintained by the Marshall County Commission and the City of Arab’s Pine Lake Village Dam within the Arab city limits.

Previous Occurrences of Dam/Levee Failures

There have been no documented dam/levee failures within Marshall County.


Probability of Future Dam/Levee Failure Events

The risks to Marshall County associated with dam/levee failure are minimal. TVA has emergency action plans in place for Guntersville and Nickajack Dams, which are constantly monitored and inspected for safety. The action plans address failures that could occur under normal conditions, a 100 year flood event, and an extreme flood event. Each plan provides for emergency response guidelines in the event of failure. The TVA plans are kept on file with the Marshall County EMA. Earthen dams maintained by the Marshall County Commission and the City of Arab pose little risk of failure.

Major earthquakes in Marshall County and East Tennessee have some potential to threaten Marshall County dams and Nickajack Dam. Refer to the hazard profile for earthquakes for the probability of these future events.

Map 5-18. Dams/Levees


Map 5-19. Dam Failure Inundation Areas

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5.4.9 Landslides

Marshall County, with over 200 feet in elevation differences between the low-lying lands along Lake Guntersville and the Tennessee River and surrounding mountain tops, has vast areas of steep and rugged terrain. Rugged areas, such as these, are usually susceptible to landslides, which is confirmed by reports of periodic occurrences of landslides over the last 40 years.

The Geologic Survey of Alabama (GSA) has studied the potential for landslides throughout Alabama. Geographic Information System (GIS) data provided by the GSA for this plan, classifies landslide incident and susceptibility shown on Map 5-20 “Landslides Areas,” as follows:

1. Landslide susceptibility. Susceptibility is the probable degree of response to landslide triggers, that is, the response to cutting or excavation, loading of slopes, or to unusually high rainfall. Generally, unusually high rainfall or changes in existing conditions can initiate landslide movement in areas where rocks and soils have experienced numerous landslides in the past. The potential for landslides is classified into one of the following categories:

2. Landslide incidence. Landslide incidence is the number of landslides that have occurred. These areas are classified according to the percentage of the area affected by landslides, as follows:

Location of Potential Landslides

As shown on Map 5-20 “Landslide Areas,” almost the entire county has some degree of susceptibility to landslides, and incidences appear random. The degrees of susceptibility and incidence vary, however, as explained in the next section on the extents of the landslide hazard.

Extent and Intensity of Potential Landslides

According to the GSA data, most of Marshall County is an area of moderate to high susceptibility to landslides, with the highest susceptibility in the southeast portion of the county, encompassing Albertville, Boaz, Douglas and surround unincorporated areas. These same areas, however, have a low incidence. The northwest areas of the county, including Arab, Union Grove, and Grand are moderately susceptible with a moderate incidence of landslides. Most of the City of Guntersville and some areas immediately surrounding Lake Guntersville have low susceptibility and incidence. Damage reports of reported incidents have been relatively minor.

Previous Occurrences of Landslides

There have been five instances of landslides reported in the local media since 1970. On May 13, 1978, the Arab Tribune reported that a landslide occurred on Georgia Mountain shutting down Arab Water until 9:00 Sunday. The Advertiser-Gleam reported that the weekend of April 25-26, 1970, landslides blocked roads, washed away roads, and caused water to be turned off in some areas. In 1977, a landslide affected a water tank and piping, causing $22,000 in damages and in April 1979 - $1,000 in damages occurred, according to The Advertiser-Gleam. On May 1-3, 1997 a storm caused a landslide ruining roadways, as reported in The Advertiser-Gleam.

GSA reports of infrequent landslides are shown on Map 5- 20 “Landslide Areas.”

Probability of Future Landslide Events

Given the terrain, record of incidents, and the widespread susceptibility of the county to landslides, the probability of future landslide occurrences is certain. According to GSA data, the areas most at risk are atop Sand Mountain - the communities of Albertville, Boaz, Douglas, and surrounding unincorporated communities. The location and annual probability of a landslide, however, are completely unpredictable and could occur anywhere within the county. Although the probable location of a landslide is widespread throughout the county, the frequency and damage potential, based on past records, is low. Consequently, the risk level of landslides is low, relative to other natural hazards affecting Marshall County.

Map 5-20. Landslide Areas

Although the GSA map data locates the general degrees of risk for landslides in Marshall County, the actual probability varies according to specific site locations and the presence of activities or conditions that might trigger a landslide, such as excavation, hillside development, heavy rainfall, or seismic activity. GSA records of landslides have occurred even in areas mapped as “low incidence.”

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5.4.10 Earthquakes Profile

Earthquakes are not uncommon in Alabama, with hundreds of recorded events since 1886. Most of these Alabama earthquakes have been associated with the Southern Appalachian Seismic Zone, as shown on Map 5-21 “Seismic Zones.” Although the Southern Appalachian Seismic extends into an area of low seismic hazard in northern and central Alabama, the impacts of Alabama”s largest earthquake of record, the 5.1 magnitude Irondale earthquake of 1916, could be felt in Marshall County and far beyond. The April 29, 2003, earthquake near Fort Payne measured 4.9 in magnitude in adjacent Dekalb County. Many aftershocks followed.

Map 5-21. Seismic Zones

Source: Geological Survey of Alabama, Geohazards Program

Location of Potential Earthquakes

All of Marshall County has a low degree of susceptibility to earthquakes, but the impacts can vary depending on the magnitude and epicenter location. The following maps, generated from 2008 GIS data supplied by the Geological Survey of Alabama (GSA), show locational variations in ground shaking and soil liquefaction throughout Marshall County. Damages to buildings and infrastructure depend not only on the energy released during an earthquake but also underlying soils and geological characteristics. For instance, structures built upon loose sediments of riverine floodplains along the Tennessee River and Lake Guntersville are more likely to be damaged than structures built on bedrock in the upper elevations, such as Sand Mountain. Liquefaction is most likely to occur in soils with high water content within parts of these flood plains. Given the natural physical features of Marshall County, ground shaking potential and seismic liquefaction susceptibility are very low in all developed municipal locations.

Map 5-22. Earthquake Ground Shaking Potential

Map 5-23. Earthquake Liquefaction Potential

Extent and Intensity of Potential Earthquakes

According to the Geological Survey of Alabama (GSA), recent seismograph records indicate that earthquakes are frequent but not strong enough to be felt on the land surface. Earthquakes can occur anywhere at any time in Alabama, but most are likely to do little or no damage. Damage reports of incidents have been relatively minor. Potential impacts of earthquakes could result from damages to Guntersville Dam. As discussed in Section 5.3.11 “Earthquakes Description” in this chapter, the severity of an earthquake is measured according to the Modified Mercalli Intensity Scale, shown again in Table 5-21 below, and the magnitude is the measure of energy released by the earthquake on a scale of 1 to 10, with a magnitude 4 being felt on land and causing some damage.

Table 5-21. Modified Mercalli Intensity Scale

Source: Geological Survey of Alabama

Map 5-24. Peak Ground Acceleration


Ground motion maps are often used to assess the magnitude and frequency of seismic events. These maps measure the probability of exceeding a peak ground motion measured as peak ground acceleration (PGA) within a given period of years. The Peak Ground Acceleration (PGA) map (Map 5-24) for Alabama shows the potential severity of earthquakes in northeast Alabama. Marshall County’s severity for a 50 year/2% probabilistic event is moderately low at 12-14% g, where % g is percentage of the total horizontal ground acceleration of the earthquake event.


Previous Occurrences of Earthquakes

Map 5-25. &ldquo:Alabama Earthquake Locations” shows the location and magnitude of recorded earthquakes from 1886 through May, 2009. Very few earthquakes with a magnitude greater than 4.0 have been recorded. Table 5-22 “Historical Earthquakes” lists earthquakes of records from 1886 through May 2009 for Marshall and surrounding counties. Only the Fort Payne earthquake of 2003 measured over 4.0 in magnitude, and only four minor events occurred within Marshall County over this 123 year period.

Map 5-25. Alabama Earthquake Locations


Table 5-22. Historical Earthquakes, 1886-2009

Date

County

Nearest City or Town

Magnitude

Impacts/Notes

2/4/1886

DeKalb

Valley Head

-

(III)

6/16/1927

Jackson

Scottsboro

-

(IV)

6/24/1939

Madison

Huntsville

-

(IV)

4/23/1957

Madison

Farley

-

(VI)

2/18/1964

DeKalb

Ala.-Ga.

-

(IV)

9/28/1975

Blount

Cedar Springs

-

(VI)

5/7/1981

Cullman

Cullman

2.1

Not felt

8/9/1984

Madison

Huntsville

2.9

Not felt

8/24/1984

Madison

Huntsville

1.4

Not felt

8/26/1984

Jackson

Mud Creek

1.3

Not felt

2/19/1985

Jackson

Bridgeport

1.1

Not felt

1/28/1986

Blount

Hendrix

0.9

Not felt

9/3/1986

Jackson

Fackler

1.8

Not felt

11/7/1987

DeKalb

Fort Payne

1.2

Not felt

2/3/1987

Jackson

Hollytree

2.4

Not felt

2/20/1989

Madison

Huntsville

1.3

Not felt

4/23/1989

Cullman

Jones Chapel

1.7

Not felt

6/11/1989

Jackson

Stevenson

0.8

Not felt

9/26/1989

Cullman

Lewis Smith Lake

1.7

Not felt

12/15/1990

Morgan

Decatur

1.8

Not felt

1/21/1991

Marshall

Guntersville Dam

1.9

Not felt

3/28/1991

Madison

Huntsville

1.8

Not felt

11/4/1991

Cullman

Cullman

2.3

Not felt

11/10/1991

DeKalb

Dugout Valley

1.8

Not felt

11/17/1991

Cullman

Cullman

1.9

Not felt

3/17/1992

Morgan

Decatur

2

Not felt

4/20/1994

Blount

Blount Springs

2.3

Not felt

5/25/1994

Jackson

Stevenson

2.3

Not felt

7/4/1994

Marshall

Guntersville

0.8

Not felt

10/5/1994

Jackson

Scottsboro

1.2

Not felt

7/31/1997

Jackson

Stevenson

1.6

Not felt (possible blasting event)

8/20/1997

Jackson

Scottsboro

2.3

8 mi SE of Scottsboro

9/14/1997

DeKalb

Fort Payne

1.6

 

5/10/1998

Etowah

Gadsden

2.5

 

7/30/1998

Jackson

Scottsboro

2

7 mi west of Scottsboro

10/22/1998

Jackson

Scottsboro

1.6

Scottsboro

10/11/1999

Blount

Oneonta

2.5

16 km (10 mi) NE of Oneonta

4/21/2000

Blount

Oneonta

2.4

12 km (7 mi) SW of Oneonta

3/12/2001

Marshall

Guntersville

2.3

9 miles (15 km) NW of Guntersville

6/21/2001

Jackson

Stevenson

2.3

3 miles (5 km) W of Stevenson

9/10/2001

Marshall

Guntersville

1.7

10 miles (16 km) NE of Guntersville

12/7/2001

Jackson

Scottsboro

1.6

11 miles (18 km) WNW of Scottsboro

12/24/2001

Jackson

Scottsboro

2.4

12 miles (19 km) WNW of Scottsboro. Only 24 miles (38 km) to TVA dam at Guntersville

2/4/2003

Jackson

Scottsboro

1.9

 

4/29/2003

DeKalb

Mentone

4.9

10 miles (15km) ENE of Fort Payne

6/22/2003

DeKalb

Fort Payne

1.9

7 miles (12 km) NNE of Fort Payne

7/6/2003

DeKalb

Mentone/aftershock

2.4

 

7/15/2003

DeKalb

Mentone/aftershock

2.5

 

7/25/2003

DeKalb

Rainsville

2

12 miles WSW of Rainsville

8/16/2003

DeKalb

Alpine/aftershock

2

 

6/21/2004

DeKalb

Fort Payne

2.2

3 miles NE of Fort Payne

11/23/2006

Jackson

Larkinsville

1.8

18 Scottsboro, AL - 9km (5 miles) WNW (289 degrees)

6/2/2008

Jackson

Dutton

2.2

5 km (3 mi) NNW of Dutton, AL

7/18/2008

Jackson

Francisco

2.3

4.7 km (2.9 mi) WSW of Francisco, AL

8/1/2008

Jackson

Lim Rock

2.3

1.7 km (1 mi) SW of Lim Rock, AL

5/3/2009

Jackson

Woodville, AL

2.2

4 km (2 miles) NNE (20°) from Woodville, AL

Map 5-26 “1916 Irondale Earthquake” below shows the impact of the of the 1916 Irondale earthquake on Marshall County, where the measured intensity was between IV and V, where the shaking was felt and some disruption occurred. This scenario was also evaluated using the HAZUS-MH earthquake module, and the ground shaking results, measure in Peak Ground Acceleration, in Marshall County are shown on Map 5-27 “Marshall County PGA for 1916 Earthquake.”

Map 5-26. 1916 Irondale Earthquake

Source: U.S Geological Survey

Map 5-27. Marshall County PGA for 1916 Earthquake


On Tuesday morning, April 29, 2003, a 4.9 magnitude earthquake occurred near Fort Payne, in DeKalb County, Alabama, an adjacent county directly west of Marshall County. This earthquake was felt in 13 states, as shown on Map 5-28 “2003 Regional Earthquake Impacts.” Fortunately, the earthquake was deep and consequently did not cause significant structural damages in Fort Payne, the closest major city.

Map 5-28. 2003 Regional Earthquake Impacts

To assess the impacts of the 2003 Fort Payne Earthquake, 10 miles north of Fort Payne, in adjacent Dekalb County, the USGS prepared a “Community Internet Intensity Map,” which is shown below as Map 5-29. According to the USGS, the “Community Internet Intensity Map (CIIM) summarizes the online questionnaire responses provided by Internet users. An intensity number is assigned to each community from which a filled-out CIIM questionnaire was received; each intensity value reflects the effects of earthquake shaking on the people and structures in the community. The color-coded ZIP Code zone on the map represents the average of the individual intensity values in that ZIP Code zone.”


Map 5-29. 2003 Fort Payne Earthquake Intensity

Probability of Future Earthquake Events

Although the GSA records show frequent earthquake occurrences in the vicinity of Marshall County, the probability of damaging earthquakes is not at all likely. Even though the probability of an event is high - Marshall County can expect occasional incidents - the likelihood of a high magnitude earthquake is extremely low. The historical probability of a damage-causing earthquake with a magnitude exceeding 5.0 within close enough proximity to Marshall County confirms the unlikelihood of a damaging event. Only one earthquake of record in 1916 has exceeded a 5.0 magnitude over the last 123 years and that was in Irondale.

According to GSA records and GIS map data, the areas of Marshall County most susceptible to damages from ground shaking and liquefaction are areas of wet soils within the flood plains along the Tennessee River and parts of Lake Guntersville. First, however, an earthquake of great enough magnitude would need to take place within close enough proximity to Marshall County. The probability of such an event is not very likely; consequently, all developed areas within the incorporated areas of Marshall County have extremely low risks of earthquake damages. The results of the Hazard Mitigation Planning Committee Hazard identification and Ratings (See Appendix D) supports this same conclusion by giving an average rating for all jurisdictions of low for both probability and extents.

5.4.11 Sinkholes (Land Subsidence) Profile

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Map 5-30. Limestone Outcrops in Alabama
Source: Geological Survey of Alabama

Marshall County, located in the northeast part of the state, is covered with a significant amount of limestone formations (see Map 5-30 “Limestone Outcrops in Alabama”). When limestone interacts with underground water, the water dissolves the limestone to form karst topography which is an amalgamation of caves, underground channels, and a rough and bumpy ground surface. The underground water carves channels and caves that are susceptible to collapse from the surface. Alabama contains over 2,000 caves because of the karst topography. See

Building on or near karst areas can pose potential problems and great expense because of damage to buildings or cave-ins forming along roads. When subsidence occurs in developed areas, it can have a significant community impact s, including loss of property value, increased cost of insurance and potential injury.

According to the Geological Survey of Alabama, Marshall County is located almost entirely within an area of high sinkhole activity and subsistence, as shown on Map 5-31 “Active Sinkhole Areas in Alabama.”

Map 5-31. Active Sinkhole Areas in Alabama

Source: The Geological Survey of Alabama
http://www.gsa.state.al.us/gsa/geologichazards/sinkholes/sinks2.html

In general, the primary cause of land subsidence is human activity. The human activities that may trigger subsidence include mining and the withdrawal of groundwater. Vibrations from machinery, cars, and drilling equipment can exacerbate sinkholes. GSA geologists estimate that the substantial increase in sinkhole activity in Alabama since 1950 parallels the period of the State’s greatest economic growth.

In addition to human activity, droughts and excessive rainfall can also lead to the formation of sinkholes. According to University of Alabama at Birmingham (UAB) geologist Scott Brande, Ph.D., much of the recent sinkhole activity in Alabama is likely due to the drought of the summer of 2000. Another major period of droughts occurred in 2007 and 2008. During a drought, the groundwater table falls and caves that are normally filled with water may lose the support that the water provided. Eventually, cracks formed during the drought period will cause the roof of the cavity to fail.

Location of Potential Sinkholes

According to a statewide study of sinkholes completed in 1977 by the GSA, land subsidence has occurred in approximately three-quarters of the county. Map 5-31 “Marshall County Sinkhole Susceptibility” shows a concentration of sinkholes in the northern and northwestern parts of the county with many sinkholes occurring along the banks of the Tennessee River and the shores of Lake Guntersville.

Extent and Intensity of Potential Sinkholes

Large areas of Marshall County are susceptible to the development of sinkholes. Those that do occur are primarily due to the limestone formations or from underground mines. When subsidence occurs in developed areas, it can have a significant impact on the communities including loss of property value, increased cost on insurance and potential injury. Sinkholes usually create minor nuisances but have the potential to cause substantial damages and destruction of buildings and infrastructure, including roads, bridges, and utility lines. The communities of Grant, Guntersville, and Union Grove are in areas of highest susceptibility.

Previous Occurrences of Sinkholes

The GSA estimates over 4,000 sinkholes in Alabama; however, no historic data has been compiled in Marshall County since the 1977 study. Further, little documentation about recent sinkhole activities has been archived. To address this informational gap, the GSA is currently creating a new statewide inventory of sinkholes.

Of the available records, several sinkholes have been reported in or in close proximity to Guntersville. The largest sinkhole in the county is in Grant, with other large sinkholes along Highway 231 and around the unincorporated communities of Ruth and Oleander. In fact, one of Alabama’s largest caves and leading tourist attractions, Cathedral Caverns is located near Grant.

Northeast of Guntersville is a well-known sinkhole located in Bucks Pocket State Park along a trail that leads to Point Rock. Another location of sinkholes, caves and other karst features is the Honeycomb Creek Small Wild Area which covers 274 acres and is a popular whitewater rafting recreation area. It is located along CR 593 north of Guntersville Lake.

Probability of Future Sinkhole Events

The probability of future occurrences cannot be accurately predicted. Sinkholes are random events, which can be influenced by man's activity, ground water withdrawals, or drought. However, because the county has active sinkholes within areas of increasing urbanization, the probability of future events will likely remain high, and past trends will likely continue. According to the FEMA insurance reports, the number of sinkholes in the U.S. has steadily increased over the last several decades, and insurance claims for damages as a result of sinkholes have increased dramatically. The new data collection efforts by the Geological Survey of Alabama may help geologists better predict sinkhole activity within Marshall County.

Map 5-32. Marshall County Sinkhole Susceptibility

(The information presented in this section was derived from the following sources: Geological Survey of Alabama, Geological Hazards Program, Sinkholes and Subsistence; “On Shaky Ground: Alabama's Sinkhole Heritage,” UAB Magazine, Winter 2002 (Volume 22, Number 1) by Kathleen Yount; “Induced and Natural Sinkholes in Alabama ” A Continuing Problem Along Highway Corridors,” Accession Number 00158164, Transportation Research Board, Washington, DC.; Alabama Department of Conservation and Natural Resources, Montgomery, Alabama.)

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5.4.12 Man-Made Hazards Profile

From 1989 through 2007, there have been 63 hazardous materials releases in Marshall County. Twenty-one of those have occurred on the Tennessee River. The potential impact from a major release on the river and Lake Guntersville can be far reaching. Depending on the location and type of material accident, the water supply for those who depend on the river could become contaminated and many of the fish and wildlife that live in or near the river and lake could be in danger.

Hazardous material accidents are the main type of man-made hazard that concerned the Hazard Mitigation Planning Committee (HMPC) members, as reported in the hazard identification exercise (see Appendix D “HMPC Identification and Ratings) and discussed at committee meetings. These types of man-made accidents are the ones that occurred most often. The accidents range from manufacturing to storage to transportation to delivery. From April 19 through May 7, 2007, a grain bin silo was on fire, which presented the threat of explosion. There have been fuel spills at gas stations that required clean up by the local fire stations, and there has been a diesel pipeline leaking into a stream. There have been instances of people burning materials that are dangerous to the air and abandoned drums have been found with hazardous materials leaking out of them. There have been multiple motor accidents with tanker trucks or other vehicles with large quantities of hazardous materials.

In addition to the hazardous material accidents, there have been hostage situations and bomb threats. These have all been local incidents which were resolved quickly. Some of the HMPC members did report that they feel a threat from terrorism due to their proximity to Redstone Arsenal in Huntsville. The Arsenal does rate highly as a potential target for a terrorist attack and, depending on the type of attack; the residual effects could possibly spread to Marshall County.

Location of Potential Man-Made Hazards

All Marshall County jurisdictions are subject to man-made hazards and equally at risk. There are 79 facilities listed in CAMEO. CAMEO is a listing provided by the EPA on places in which hazardous chemicals are stored; however, the listing does not include gasoline stations. These 79 facilities are found throughout the county with most of them located within the main cities of Arab, Albertville, Boaz, and Guntersville. They range from the neighborhood hardware store which might sell fertilizer to the chemical manufacturing plant. Those locations all have the potential to have a spill or accident of some type that could lead to a hazardous chemical release. In addition to the fixed facilities, there are trains that transport hazardous materials through Marshall County as well as the many tractor trailers that haul similar materials across the county. The area that has had the most releases throughout the years is the Tennessee River. See Map 5-32 “Hazardous Materials Storage.”

As described above, hazardous materials events can occur anywhere those materials are manufactured, stored, or transported. Also, depending on the type of material, the threat could be far reaching if it is able to be transported through the air or water.

Acts of terrorism can occur anywhere at any time and therefore there is the potential for an attack on anyone living in Marshall County.

Extent and Intensity of Potential Man-Made Hazards

Marshall County has a number of hazardous materials events per year ranging from chemicals released in the air from burning tires to fuel spills in the Tennessee River. The events occur throughout the county, and some of them are caused by people deliberately performing an action that releases the chemical without regard its impact on the air and water. The extent of technological hazards impacts and terrorist attacks can be quite severe, with potential for widespread damage to property and infrastructure and major loss of life and casualties, within any jurisdiction.

Previous Man-Made Hazard Occurrences

The principal man-made hazard events that have occurred in Marshall County are hazardous materials accidents. These have occurred at manufacturing sites, storage sites, and even during transport. In 2007 the Marshall County EMA director stated that within the last 18 years there had been 63 hazardous materials incidents with 21 of them happening on the Tennessee River. In addition to the typical facilities such as plants, warehouses, and stores, there has been an increase in hazards at residences and even hotels in the manner of methamphetamine laboratories. These labs have been stationed in residences and are even mobile. They provide a unique threat when they are in transit as there are no markings on the vehicles to let other people in the surrounding area know there is a potential danger.

There have been other occasional man-made occurrences in Marshall County - a hostage crisis and a bomb threat. The principal man-made hazard threats, however, are accidental releases of a hazardous material.


Probability of Future Man-Made Hazard Events

One of the hardest features to grasp of a man-made hazard is it unpredictability. There is no way to determine if there is going to be a man-made hazard at any certain time. For many natural hazards there is a season (e.g., hurricanes and tornadoes), a map of probable locations (e.g., floods and earthquakes) or forecasts (e.g., severe storms). For man-made hazards, events can happen anytime and virtually anywhere, and they do not need any specific circumstances in which to occur.


Map 5-33. Hazardous Materials Storage

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5.5 Summary of Hazards and Community Impacts

Table 5-23 “Summary of Hazards and Community Impacts” in this section presents an overview of each Marshall County jurisdiction's vulnerability to the hazards identified in this Plan. Community impacts include the following descriptions and measurements:



Table 5-23. Summary of Hazards and Community Impacts

Hazard Jurisdiction Community Impacts Impacts on Vulnerable Community Buildings, Critical Facilities, and Infrastructure
Location (Geographic Extent of Hazard in the Community) Probability (Frequency of Hazard Occurrence in the Community) Extent (Magnitude or Severity of Hazard in the Event of Occurrence) Level of Exposure (Degree of Structures Exposed to the Hazard) Level of Damage Potential (Percentage of Likely Damage to Exposed Structures)

Tornadoes

Marshall County

Community-wide

High

Very Severe

High

High

Albertville

Community-wide

High

Very Severe

High

High

Arab

Community-wide

High

Very Severe

High

High

Boaz

Community-wide

High

Very Severe

High

High

Douglas

Community-wide

High

Very Severe

High

High

Grant

Community-wide

High

Very Severe

High

High

Guntersville

Community-wide

High

Very Severe

High

High

Union Grove

Community-wide

High

Very Severe

High

High

Unincorporated Communities

Community-wide

High

Very Severe

High

High

Severe Storms

Marshall County

Community-wide

Very High

Moderately Severe

High

Low

Albertville

Community-wide

Very High

Moderately Severe

High

Low

Arab

Community-wide

Very High

Moderately Severe

High

Low

Boaz

Community-wide

Very High

Moderately Severe

High

Low

Douglas

Community-wide

Very High

Moderately Severe

High

Low

Grant

Community-wide

Very High

Moderately Severe

High

Low

Guntersville

Community-wide

Very High

Moderately Severe

High

Low

Union Grove

Community-wide

Very High

Moderately Severe

High

Low

Unincorporated Communities

Community-wide

Very High

Moderately Severe

High

Low

Floods

Marshall County

Partial

Low

Somewhat Severe

Low

Medium

Albertville

Partial

Moderate

Moderately Severe

Low

Medium

Arab

Partial

Low

Somewhat Severe

Low

Medium

Boaz

Partial

Low

Somewhat Severe

Low

Medium

Douglas

Partial

Low

Somewhat Severe

Low

Medium

Grant

Partial

Low

Somewhat Severe

Low

Medium

Guntersville

Partial

Low

Somewhat Severe

Low

Medium

Union Grove

Minimal

Very Low

Not Severe

Low

Medium

Unincorporated Communities

Partial

Moderate

Moderately Severe

Low

Medium

Hurricanes

Marshall County.

Community-wide

Low

Somewhat Severe

High

Low

Albertville

Community-wide

Low

Somewhat Severe

High

Low

Arab

Community-wide

Low

Somewhat Severe

High

Low

Boaz

Community-wide

Low

Somewhat Severe

High

Low

Douglas

Community-wide

Low

Somewhat Severe

High

Low

Grant

Community-wide

Low

Somewhat Severe

High

Low

Guntersville

Community-wide

Low

Somewhat Severe

High

Low

Union Grove

Community-wide

Low

Somewhat Severe

High

Low

Unincorporated Communities

Community-wide

Low

Somewhat Severe

High

Low

Winter Storms/Freezes

Marshall County

Community-wide

Moderate

Severe

High

Low

Albertville

Community-wide

Moderate

Severe

High

Low

Arab

Community-wide

Moderate

Severe

High

Low

Boaz

Community-wide

Moderate

Severe

High

Low

Douglas

Community-wide

Moderate

Severe

High

Low

Grant

Community-wide

Moderate

Severe

High

Low

Guntersville

Community-wide

Moderate

Severe

High

Low

Union Grove

Community-wide

Moderate

Severe

High

Low

Unincorporated Communities

Community-wide

Moderate

Severe

High

Low

Droughts/Heat Waves

Marshall County

Community-wide

Moderate

Somewhat Severe

High

Low

Albertville

Community-wide

Moderate

Somewhat Severe

High

Low

Arab

Community-wide

Moderate

Somewhat Severe

High

Low

Boaz

Community-wide

Moderate

Somewhat Severe

High

Low

Douglas

Community-wide

Moderate

Somewhat Severe

High

Low

Grant

Community-wide

Moderate

Somewhat Severe

High

Low

Guntersville

Community-wide

Moderate

Somewhat Severe

High

Low

Union Grove

Community-wide

Moderate

Somewhat Severe

High

Low

Unincorporated Communities

Community-wide

Moderate

Somewhat Severe

High

Low

Wildfires

Marshall County

Partial

Very High

Somewhat Severe

Medium

High

Albertville

Partial

Very High

Somewhat Severe

Medium

High

Arab

Partial

Very High

Somewhat Severe

Medium

High

Boaz

Partial

Very High

Somewhat Severe

Medium

High

Douglas

Partial

Very High

Somewhat Severe

Medium

High

Grant

Partial

Very High

Somewhat Severe

Medium

High

Guntersville

Partial

Very High

Somewhat Severe

Medium

High

Union Grove

Partial

Very High

Somewhat Severe

Medium

High

Unincorporated Communities

Partial

Very High

Severe

High

High

Dam/Levee Failures

Marshall County

Minimal

Very Low

Somewhat Severe

Low

High

Albertville

Minimal

Very Low

Not Severe

Low

High

Arab

Minimal

Very Low

Not Severe

Low

High

Boaz

Minimal

Very Low

Not Severe

Low

High

Douglas

Minimal

Very Low

Not Severe

Low

High

Grant

Minimal

Very Low

Not Severe

Low

High

Guntersville

Partial

Very Low

Somewhat Severe

Low

High

Union Grove

Minimal

Very Low

Not Severe

Low

High

Unincorporated Communities

Partial

Very Low

Severe

Medium

High

Landslides

Marshall County

Partial

Very Low

Not Severe

Low

High

Albertville

Partial

Very Low

Not Severe

Low

High

Arab

Partial

Very Low

Not Severe

Low

High

Boaz

Partial

Very Low

Not Severe

Low

High

Douglas

Partial

Very Low

Not Severe

Low

High

Grant

Partial

Very Low

Not Severe

Low

High

Guntersville

Partial

Very Low

Not Severe

Low

High

Union Grove

Partial

Very Low

Not Severe

Low

High

Unincorporated Communities

Partial

Low

Not Severe

Low

High

Earthquakes

Marshall County

Community-wide

Low

Not Severe

High

Low

Albertville

Community-wide

Low

Not Severe

High

Low

Arab

Community-wide

Low

Not Severe

High

Low

Boaz

Community-wide

Low

Not Severe

High

Low

Douglas

Community-wide

Low

Not Severe

High

Low

Grant

Community-wide

Low

Not Severe

High

Low

Guntersville

Community-wide

Low

Not Severe

High

Low

Union Grove

Community-wide

Low

Not Severe

High

Low

Unincorporated Communities

Community-wide

Low

Not Severe

High

Low

Sinkholes (Land Subsidence)

Marshall County

Partial

Low

Not Severe

Medium

High

Albertville

Minimal

Low

Not Severe

Low

High

Arab

Minimal

Low

Not Severe

Low

High

Boaz

Minimal

Low

Not Severe

Low

High

Douglas

Minimal

Low

Not Severe

Low

High

Grant

Minimal

Low

Not Severe

Low

High

Guntersville

Community-wide

Low

Not Severe

High

High

Union Grove

Minimal

Low

Not Severe

Low

High

Unincorporated Communities

Partial

Low

Not Severe

Medium

High

Man-Made Hazards

Marshall County

Community-wide

Very High

Varies

High

Varies

Albertville

Community-wide

Very High

Varies

High

Varies

Arab

Community-wide

Very High

Varies

High

Varies

Boaz

Community-wide

Very High

Varies

High

Varies

Douglas

Community-wide

Very High

Varies

High

Varies

Grant

Community-wide

Very High

Varies

High

Varies

Guntersville

Community-wide

Very High

Varies

High

Varies

Union Grove

Community-wide

Very High

Varies

High

Varies

Unincorporated Communities

Community-wide

Very High

Varies

High

Varies

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5.6 Vulnerability of Structures within Each Jurisdiction

5.6.1 Scope of Structure Inventory

This section presents an inventory of existing and future buildings, critical facilities, and infrastructure, by types and numbers, located within each identified hazard area and within each jurisdiction. For the purposes of this risk assessment, vulnerability refers to the exposure of buildings, critical facilities, and infrastructure to a particular hazard and their susceptibility to the resultant damages that could be incurred by such hazard exposure. The structure inventory in this section forms the basis for the loss estimates presented in Section 5.7 “Estimate of Dollar Losses to Vulnerable Structures.”

Most of the identified Marshall County hazards are county-wide, where exposure is generally uniform among all jurisdictions. County-wide hazards include tornadoes, severe storms, hurricanes, winter storms/freezes, droughts/heat waves, wildfires, earthquakes, and man-made hazards. Location-specific hazards, where exposure may vary among jurisdictions, are floods, sinkholes, landslides, and dam failures.

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5.6.2 Inventory Methodology

HAZUS-MH, which refers to "Hazards in the U.S. - Multi-Hazards," is a risk assessment tool developed by FEMA for analyzing potential losses from floods, hurricane winds, and earthquakes. HAZUS-MH applies scientific methods to work in concert with geographic information systems (GIS) data to produce estimates of hazard-related damages. The latest edition of HAZUS-MH software, as of March 2009, release MR-3, Patch 3, was used by the planning team to assist in this risk assessment for Marshall County. HAZUS-MH was used to as a basis for the inventory of vulnerable structures presented in this section and was also used to estimate losses presented in Section 5.7 of this document. Other GIS data supplemented the HAZUS-MH data to create a more comprehensive risk assessment. These 2009 HAZUS-MH runs update the HAZUS-MH assessments performed for the 2004 plan. The building counts and values are taken directly from the HAZUS-MH databases. Since the 2004 plan, HAZUS-MH commercial data have been updated to Dun & Bradstreet 2006, and building valuations have been updated to R.S. Means 2006 in version MR-3. Population counts are from the 2000 Census, although these have been supplemented with 2007 population estimates from the Census Bureau and 2025 projections from the Alabama State Data Center. HAZUS-MH uses system formulas to estimate counts for the building and facility categories. These HAZUS-generated counts are an approximation and do not necessarily reflect the exact count of individual buildings or facilities in each category.

Three levels of analysis are available with the HAZUS-MH software. For the purposes of this plan a Level 1 analysis was run on Marshall County. A Level 1 analysis is the basis for developing mitigation plans and policies, emergency preparedness, and response and recovery planning. At Level 1, the analysis utilizes the data provided with the software. Extensive technical knowledge is not required at this level and minimal data entry is needed. The analysis provides general information regarding earthquakes, floods, and hurricanes that affect the study region and provides an assessment as to whether or not further analysis is warranted. All numbers and calculations are based on a county-wide level, the smallest geographic area of meaningful analysis using HAZUS-MH. HAZUS-MH is best designed for large multi-county regions but can generate data on a county level, as well. Although jurisdictional level analysis is possible by compiling data for all Census tracts in the jurisdiction of interest, this small area analysis using HAZUS-MH loses reliability and is not recommended.

“Buildings,” as used in this risk assessment include all walled and roofed structures. "Critical facilities" and "infrastructure," for the purpose of this vulnerability inventory, include the following structures, as classified by HAZUS-MH:

Critical Facilities

Infrastructure

Other

Additional GIS data used in this risk assessment was compiled from data supplied by the Marshall County EMA, Marshall County Information Technology Department, Marshall County Tax Assessor, Geologic Survey of Alabama, U.S.G.S., National Weather Service, NFIP, U.S. Census Bureau, Alabama State Data Center, Tennessee Valley Authority, and the Alabama Forestry Commission, among other sources.

Much of the county-wide inventory data from HAZUS-MH have been apportioned to each jurisdiction on the basis of population distribution, as follows:

Table 5-24. Population Apportionment by Jurisdiction

Jurisdiction

2007 Population Estimate

% of Total

Marshall County

87,644

100.0%

Albertville

19,536

22.3%

Arab

7,691

8.8%

Boaz

8,213

9.4%

Douglas

579

0.7%

Grant

689

0.8%

Guntersville

8,267

9.4%

Union Grove

98

0.1%

Unincorporated

42,571

48.6%

Source:  U.S. Census 2007 Population Estimates

Future buildings, critical facilities, and infrastructure have been projected to the year 2025 on the basis of the Marshall County growth projection by the Alabama State Data Center.  Since no small area projections are available for each jurisdiction, the method described here was developed to provide a 2025 projected population for each jurisdiction.  To project populations for each jurisdiction, the distribution of the projected 29,154 increase in county-wide population is allocated according to actual population changes of each jurisdiction between 1990 and 2007.  The same allocation of population increase among the jurisdictions is assumed for the period from 2000 to 2025.  From this allocation, a projected population can be derived for each jurisdiction.  These projections establish a growth multiplier rate to estimate future conditions in 2025.  The 2025 growth multiplier is equal to 1 + the 2007-2025 percentage increases for each jurisdiction.  For example, if 1,000 residential buildings are presently exposed (based on estimates around 2007), then a 2025 Growth Multiplier of 1.35 (where a jurisdiction's population is projected to increase 35%) would project 1,350 residential buildings in 2025.  The Growth Multiplier is applied to all present day estimates to project future conditions.  This growth projection method is not precise, but it does provide a good indication of how growth might affect future exposure of structures to hazards.

Table 5-25. 2025 County Growth Projection


Projected County Growth 2000-2025

 

2000

2025

Number

Percent

Marshall County

82,231

111,385

29,154

35.5%

Source:  Alabama State Data Center

Table 5-26.  Growth Allocation by Jurisdiction

Jurisdiction

1990

2000

Estimated 2007

1990-2007 Growth

Allocation of Growth

Marshall Co.

70,832

82,231

87,644

16,812

100.0%

Albertville

14,507

17,247

19,536

5,029

30%

Arab

6,321

7,174

7,691

1,370

8%

Boaz

6,928

7,411

8,213

1,285

8%

Douglas

474

530

579

105

1%

Grant

638

665

689

51

0%

Guntersville

7,038

7,395

8,267

1,229

7%

Union Grove

156

94

98

-21

0%

Unincorporated

34,770

41,715

42,571

7,801

46%

Source:  U.S. Census Bureau

Table 5-27. 2025 Growth Projections and Multipliers

Jurisdiction

Allocation of Growth

Projected 2025

2007 - 2025 Growth Rate

2025 Growth Multiplier

Marshall County

100%

111,385

27%

1.27

Albertville

30%

26,658

36%

1.36

Arab

8%

9,590

25%

1.25

Boaz

8%

10,112

23%

1.23

Douglas

1%

816

41%

1.41

Grant

0%

689

0%

1.00

Guntersville

7%

9,929

20%

1.20

Union Grove

0%

98

0%

1.00

Unincorporated

46%

53,492

26%

1.26

Source:  Derived from Alabama State Data Center 2025 Marshall County Projection

Hazard exposure has been estimated for each of the identified hazards.  The percent exposure can be applied to the structure inventories to derive a general estimate of vulnerable structures by hazard.  Most hazards are county-wide and all remaining hazards are estimated at less than one percent, based on GIS mapped hazard areas for location-specific hazards.  In these cases, where exposure is 1% or less, a 1% exposure rate has been applied.   Although this does not yield a precise estimate, it provides a general indication of the number and types of structures exposed to each hazard within each jurisdiction.

Table 5-28. Hazard Exposure Rates by Jurisdiction

Identified Hazard

Hazard Exposure by Jurisdiction

Marshall Co.
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Unincorporated

Tornadoes

100%

100%

100%

100%

100%

100%

100%

100%

100%

Severe Storms

100%

100%

100%

100%

100%

100%

100%

100%

100%

Floods

100%

100%

100%

100%

100%

100%

100%

100%

100%

Winter Storms/Freezes

100%

100%

100%

100%

100%

100%

100%

100%

100%

Hurricanes

100%

100%

100%

100%

100%

100%

100%

100%

100%

Droughts/Heat Waves

100%

100%

100%

100%

100%

100%

100%

100%

100%

Wildfires

100%

100%

100%

100%

100%

100%

100%

100%

100%

Dam/Levee Failures

<1%

0%

0%

0%

0%

0%

0%

0%

<1%

Landslides

<1%

<1%

<1%

<1%

<1%

<1%

<1%

<1%

<1%

Earthquakes

100%

100%

100%

100%

100%

100%

100%

100%

100%

Sinkholes

<1%

<1%

<1%

<1%

<1%

<1%

<1%

<1%

<1%

Man-Made Hazards

100%

100%

100%

100%

100%

100%

100%

100%

100%

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5.6.3 HAZUS-MH Structure Inventory

General Description of the Planning Region

HAZUS-MH refers to the geographic study area as the "region," which is all of Marshall County, including all unincorporated areas and seven municipalities. A more complete description of the planning region is presented in Chapter 3 "Community Profiles." The descriptions provided here were generated by the HAZUS-MH Global Reports for county-wide assessments of earthquakes, hurricanes, and floods. The Marshall County region is generally described by HAZUS-MH, as follows:


Table 5-29. HAZUS-MH Population and Building Value Data

State

County Name

Population

Building Value (millions of dollars)

Residential

Non-Residential

Total

Alabama

Marshall

82,231

$3,707

$1,561

$5,268

Total Region

 

82,231

$3,707

$1,561

$5,268

Building Inventory

Table 5-30. HAZUS-MH Building Inventory by Occupancy

Occupancy

Count

%

Agriculture

16

0.05%

Commercial

507

1.55%

Education

14

0.04%

Government

39

0.12%

Industrial

169

0.52%

Religion

55

0.17%

Single Family Residential

25,490

77.81%

Other Residential

6,469

19.75%

Total

32,759

100.00%

Table 5-31. HAZUS-MH Building Inventory by Construction Type

Construction Type

Count

%

Wood

25,002

76.33%

Steel

403

1.23%

Concrete

89

0.27%

Precast

27

0.08%

Reinf. Masonry

141

0.43%

Unreinf. Masonry

1,486

4.54%

Manuf. Housing

5,608

17.12%

Total

32,756

100.00%

Critical Facilities Inventory

HAZUS-MH breaks critical facilities into the two groups described below and estimates the number of each type of facility.

(1) Essential facilities, which include hospitals, medical clinics, schools, fire stations, police stations and emergency operations facilities. HAZUS-MH estimates the numbers and types of essential facilities within the region, as follows:

(2) High potential loss facilities, which include dams, levees, military installations, nuclear power plants and hazardous material sites. HAZUS-MH estimates the numbers and types of high potential loss facilities, as follows:

Transportation and Utility Lifeline Inventories

HAZUS-MH breaks lifeline inventories into the two groups described below and estimates the number of each type of facility. HAZUS-MH estimates the total value of the lifeline inventory at $1.89 billion. A more detailed breakdown is provided in Table 5- “Transportation System Lifeline Inventory.”

(1) Transportation systems, which include highways, railways, light rail, bus, ports, ferry and airports. HAZUS-MH estimates the length of highways and the number of bridges, as follows:

(2) Utility systems, which include potable water, wastewater, natural gas, crude & refined oil, electric power and communications. HAZUS-MH estimates the length of pipes, as follows:

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5.6.4 Existing and Future Structure Vulnerabilities by Hazard and Jurisdiction

Buildings

The building exposure totals generated by HAZUS-MH have been distributed according to populations by jurisdiction, the Growth Multiplier for future conditions, and the percent exposure of each hazard within each jurisdiction. The results of these estimates are shown in the following tables. As previously explained in this section, these are gross estimates that show relative degree of vulnerability. The numbers provided in the HAZUS-MH reports are not based on actual field inventories, which is beyond the scope of this planning process. Many of the numbers provided by HAZUS-MH are generated from formulas based on national standards. For example, HAZUS-MH estimates 16 agricultural buildings in this predominantly agricultural community. The actual number is quite a bit higher. Where values are given for future conditions, the values are in present value dollars.

Building exposure in Marshall County is mostly residential at over 70%. This ratio should remain constant through the 2025 plan horizon.

Table 5-32. Building Exposure by Occupancy

Occupancy

Existing Exposure ($1,000)

Future Exposure ($1,000)

% of Total

Agriculture

$26,365

$33,484

0.5%

Commercial

$933,683

$1,185,777

17.7%

Education

$54,756

$69,540

1.0%

Government

$37,537

$47,672

0.7%

Industrial

$390,787

$496,299

7.4%

Religion

$118,651

$150,687

2.3%

Residential

$3,707,199

$4,708,143

70.4%

Total

$5,268,969

$6,691,591

100.0%

Building values within each jurisdiction are substantially higher in Albertville and are expected to increase according to projected population increases. Communities need to be cognizant of the increasing risks and exposure resulting from growth.

Table 5-33. Building Values by Jurisdiction

Jurisdiction

Building Value
(millions of dollars)

Existing
Residential

Future
Residential

Existing
Non-Residential

Future
Non-Residential

Existing
Total

Future
Total

Marshall Co.

$4,711

1,561

$1,984

$5,268

$6,695

$4,711

Albertville

$1,129

$348

$475

$1,175

$1,603

$1,129

Arab

$407

$137

$171

$464

$579

$407

Boaz

$428

$147

$181

$44

$54

$428

Douglas

$37

$11

$16

$37

$52

$37

Grant

$30

$12

$12

$42

$42

$30

Guntersville

$418

$147

$177

$495

$595

$418

Union Grove

$4

$2

$2

$5

$5

$4

Unincorporated

$2,264

$759

$954

$2,560

$3,217

$2,264

Note: Totals of all municipalities and unincorporated areas may not equal Marshall County totals due to rounding.

Table 5-34. Building Count by Occupancy and Jurisdiction

Jurisdiction

Building Count by Occupancy

Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future

Agric.

Commer-
cial

Educ.

Govt.

Indus-
trial

Religion

Single Family

Other
Resid.

Marshall Co.

16

20

507

644

14

18

39

50

169

215

55

70

25,490

32,395

6,469

8,221

Albertville

4

5

113

154

3

4

9

12

38

52

12

19

5,684

7,756

1,443

1,969

Arab

1

1

45

56

1

1

3

4

15

19

5

6

2,243

2,797

569

710

Boaz

2

2

48

59

1

1

4

5

1

1

5

7

2,396

2,950

608

749

Douglas

0

0

4

6

0

0

0

0

1

1

0

1

178

251

45

63

Grant

0

0

4

4

0

0

0

0

1

1

0

1

204

204

52

52

Guntersville

2

2

48

58

1

1

4

5

16

19

5

8

2,396

2,878

608

730

Union Grove

0

0

1

1

0

0

0

0

0

0

0

0

25

25

6

6

Unincorporated

8

10

246

309

7

9

19

24

82

103

27

29

12,388

15,566

3,144

3,951

Note: Totals of all municipalities and unincorporated areas may not equal Marshall County totals due to rounding.

Table 5-35. Building Exposure by Jurisdiction and Hazard

Identified Hazard

Building Exposure ($ millions) by Jurisdiction

Marshall Co.
Albertville
Arab
Boaz
Douglas
Grant
Guntersville
Union Grove
Unincorporated 
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future
Existing
Future

Tornadoes

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Severe Storms

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Floods

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Winter Storms/Freezes

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Hurricanes

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Droughts/Heat Waves

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Wildfires

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Dam/Levee Failures

328

416

0

0

0

0

0

0

0

0

0

0

0

0

0

0

159

173

Landslides

328

416

73

111

29

37

31

44

2

3

3

3

31

45

0

0

159

173

Earthquakes

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Sinkholes

328

416

73

111

29

37

31

44

2

3

3

3

31

45

0

0

159

173

Man-Made Hazards

32,759

41,633

7,305

11,059

2,883

3,733

3,065

4,377

229

314

262

302

3,079

4,504

33

39

15,921

17,325

Note: Totals of all municipalities and unincorporated areas may not equal Marshall County totals due to rounding.

HAZUS-MH estimates close to 100 critical facilities existing within Marshall County, all of which are exposed to the county-wide hazards and are most at risk of damage from tornadoes and severe storms. Additional facilities will be added as population increases to as many at 133.

Table 5-36. HAZUS-MH Essential Facilities Data

Classification

Existing Estimate

Future Estimate

Hospitals

2 (192 total bed capacity)

2-3 (244 bed capacity)

Schools

32

41

Emergency Ops. Centers

2

2

Police Stations

10

13

Fire Stations

21

27

Table 5-37. HAZUS-MH High Potential Loss Facilities Data

Classification

Existing Estimate

Future Estimate

Dams

5 (1 classified "high hazard")

5 (1 classified "high hazard")

Hazard Materials Sites

37

47

Military Installations

0

0

Nuclear Power Plants

0

0

Infrastructure

Infrastructure inventories estimated by HAZUS-MH are presented in the following table. Infrastructure expansion is not directly related to population growth; consequently no projections are given here for future conditions. Most of the at-risk transportation system components are highway road segments and bridges, which are most threatened by flash flooding.

Table 5-38. HAZUS-MH Transportation Systems Lifeline Inventory

System

Component

# Locations/Segments

Replacement Value (millions of dollars)

Highway

Bridges

116

$87.50

Segments

74

$1,085.30

Tunnels

0

$0.00

 

Subtotal

$1,172.80

Railways

Bridges

0

$0.00

Facilities

11

$21.60

Segments

13

$20.00

Tunnels

0

$0.00

 

Subtotal

$41.60

Light Rail

Bridges

0

$0.00

Facilities

0

$0.00

Segments

0

$0.00

Tunnels

0

$0.00

 

Subtotal

$0.00

Bus

Facilities

0

$0.00

 

Subtotal

$0.00

Ferry

Facilities

0

$0.00

 

Subtotal

$0.00

Port

Facilities

16

$31.40

 

Subtotal

$31.40

Airport

Facilities

2

$9.80

Runways

2

$55.90

     

Subtotal

$65.70

   

Total

$1,311.60

Utility systems most likely to incur damages or disruptions during hazard events are wastewater treatment plants, water treatment and distribution facilities, and electric power lines and substations. Tornadoes, severe storms, and winter storms/freezes pose the greatest threat to these facilities in Marshall County.

Table 5-39. HAZUS-MH Utilities Systems Lifeline Inventory

System

Component

# Locations / Segments

Replacement value (millions of dollars)

Potable Water

Distribution Lines

NA

$63.30

Facilities

2

$59.90

Pipelines

0

$0.00

Subtotal

$123.20

Waste Water

Distribution Lines

NA

$38.00

Facilities

7

$419.60

Pipelines

0

$0.00

Subtotal

$457.60

Natural Gas

Distribution Lines

NA

$25.30

Facilities

0

$0.00

Pipelines

0

$0.00

Subtotal

$25.30

Oil Systems

Facilities

0

$0.00

Pipelines

0

$0.00

Subtotal

$0.00

Electrical Power

Facilities

1

$99.00

Subtotal

$99.00

Communication

Facilities

8

$0.70

Subtotal

$0.70

Total

$705.70

The maps on the following pages show the location and distribution of critical facilities and infrastructure throughout Marshall County and its seven municipalities. The following structure information has been assembled in GIS and mapped:

Table 5-40. Emergency Services Facilities

Agency

Type

Address

City

Marshall County E911

E911

655 4th Ave NW

Arab

Marshall County Emergency Mgmt

EMA

424 Blount Ave

Guntersville

Albertville Fire Dept

Fire

212 S Broad St

Albertville

Arab Fire Dept

Fire

653 4th Ave NW

Arab

Asbury Volunteer Fire Dept

Fire

4104 Martling Gap Rd

Albertville

Beulah Volunteer Fire Dept

Fire

2686 Beulah Rd

Boaz

Boaz Fire Dept

Fire

201 Brown St

Boaz

Douglas Fire Dept

Fire

55 Al Highway 168

Douglas

Georgia Mountain Vol Fire Dept

Fire

2485 Georgia Mountain Rd

Guntersville

Grant City Fire Dept

Fire

50 6th St W

Grant

Guntersville Fire Dept

Fire

1745 Blount Ave

Guntersville

Guntersville Fire Station 2

Fire

1745 Blount Ave

Guntersville

Hebron Fire Dept

Fire

90 Hebron School Rd

Grant

MT Hebron Volunteer Fire Dept

Fire

3038 Mount Hebron Rd

Boaz

Nixon Chapel Fire Dept

Fire

7925 Nixon Chapel Rd

Uninc. Horton

Pleasant Grove Volunteer Fire

Fire

7275 Section Line Rd

Albertville

Ruth Volunteer Fire Dept

Fire

3075 Matt Morrow Rd

Arab

South Sauty Volunteer Fire

Fire

122 Murphy Hill Dr

Uninc. Langston

Swearengin Fire Dept

Fire

5120 Swearengin Rd

Uninc. Swearingin

Union Grove Fire Dept

Fire

3680 Union Grove Rd

Union Grove

Wakefield Volunteer Fire Dept

Fire

777 S Sauty Rd

Uninc. Langston

4C Volunteer Fire Dept

Fire

3921 Brashiers Chapel Rd

Arab

Albertville Police Dept

Police

201 S Broad St

Albertville

Arab Police Dept

Police

740 N Main St

Arab

Boaz Police Dept

Police

101 Line Ave

Boaz

Douglas Fire Dept

Fire

55 Al Highway 168

Douglas

Grant Police Dept

Police

4766 Main St

Grant

Guntersville Drug Enforcement Unit

Police

435 Blount Ave

Guntersville

Guntersville City Police Dept

Police

340 Blount Ave

Guntersville

Marine Police

Police

4242 Aubrey Carr Scenic Dr

Guntersville

Marshall County Sheriff's Dept

Police

423 Blount Ave

Guntersville

Tennessee Valley Police Div

Police

50 Snow Point Rd

Guntersville

Arab Ambulance Business Office

Rescue

653 4th Ave NW

Arab

Arab Ambulance Svc

Rescue

740 N Main St

Arab

Arab Rescue Squad

Rescue

230 3rd Ave NW

Arab

Guntersville Rescue Squad

Rescue

2350 Miller St

Guntersville

Union Rescue Squad

Rescue

500 Double Bridges Rd

Boaz

Source: 2008 Polk City Directory


Map 5-34. Government Facilities

Map 5-35. Emergency Services Facilities

Map 5-36. Medical Care Facilities

Map 5-37. Emergency Shelters

Map 5-38. Schools

Map 5-39. Elderly Care and Living Facilities

Map 5-40. Communications Facilities

Map 5-41. Warning Sirens

Map 5-42. Gas and Electric Utilities

Map 5-43. Water and Sewer Facilities

Map 5-44. Transportation System Facilities

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5.7 Estimate of Dollar Losses to Vulnerable Structures

5.7.1 Scope and Purpose of Loss Estimates

The section provides a monetary estimate of the losses to the vulnerable structures identified in Section 5.6 "Vulnerability of Structures within each Jurisdiction." These estimates include losses for each identified hazard and within each jurisdiction. This component of the risk assessment examines vulnerability of buildings, critical facilities, and infrastructure and their resultant damage losses that could be incurred by exposure to each hazard. To the furthest extent possible, where data availability and methods permit, these estimates include structure, contents, and function losses and present total loss estimates for each of the inventoried assets.

For the purposes of this vulnerability assessment of dollar losses, "structure loss" attempts to measure % Damage X $ Replacement Value of the Structure. "Content loss' refers to % Damage X $ Replacement Value of the Contents. "Functional Losses" are generalized estimates of the indirect effects of the hazard, which is measured as the estimated days of interruptions in operations or downtime that an asset incurs during an event.

For hazards where historical damage records are limited, damages resulting from the most probable severity or a typical or average event have been estimated. For location specific events, such as floods, the affected parts of each jurisdiction have been evaluated. Although these estimates are very broad, they can be useful in assessing the generalized benefits and costs associated with a proposed mitigation project. Moreover, these estimates provide a basis for selecting and prioritizing actions recommended by the Mitigation Strategy in Chapter 6.

This section also describes the methodology used to prepare each of the estimates. Limitations due to insufficient data availability or lack of reliable methods have been noted. Mitigation measures for compiling and analyzing data for improved risk assessment studies have been identified in Section 5.7.5 "Recommended Risk Assessment Measures."

As explained in other sections of this Risk Assessment, most of the identified Marshall County hazards are county-wide, where exposure is generally uniform among all jurisdictions. County-wide hazards include tornadoes, severe storms, hurricanes, winter storms/freezes, droughts/heat waves, wildfires, earthquakes, and man-made hazards. Location-specific hazards, where exposure may vary among jurisdictions, are floods, sinkholes, landslides, and dam/levee failures.

5.7.2 Loss Estimate Methodology

Method 1: HAZUS-MH Loss Estimates

HAZUS-MH, which was used to as a basis for the inventory of vulnerable structures presented in Section 5.6 of this Risk Assessment was also used to estimate losses presented here. These 2009 HAZUS-MH loss estimates update the estimates performed for the 2004 plan. HAZUS-MH uses general approximation methods and system formulas to estimate losses. Consequently, the HAZUS-MH results do not accurately reflect actual losses. These types of loss estimates are best used to judge relative hazard risks and structure exposure and are useful in identifying potential mitigation actions.

Three levels of analysis are available with the HAZUS-MH software, with each level requiring a greater level of local data. For the purposes of this plan, however, a Level 1 analysis was performed for Marshall County and is sufficient for mitigation policy planning purposes. In a Level 1 analysis, the national data set provided with HAZUS-MH is used. The analysis provides general loss estimates for earthquakes, floods, and hurricane winds. All loss estimates are at a county-wide level, the smallest geographic area of meaningful analysis using HAZUS-MH.

Method 2: Estimates Based upon Historical Records

Historical event records and damage data obtained from Section 5.4 "Hazard Profiles" supplemented the HAZUS-MH data to create a more comprehensive foundation for assessing the damage impacts of hazards and preparing some of these loss estimates. Damage data and records of previous occurrences were obtained from the following primary sources:

  1. NFIP insurance claims data since 1978 (see Section 5.9);
  2. NOAA, National Climatic Data Center damage estimates (see damage summaries in Section 5.6 "Hazard Profiles" and Appendix E "Hazard Profile Data."
  3. National Weather Service Alabama Tornado database.
  4. Alabama State Hazard Mitigation Plan, 2007 update, section 5.5 "Vulnerability Assessment and Loss Estimation."

Local news accounts , discussions with Hazard Mitigation Planning Committee members, and local survey responses were likewise reviewed for reports of economic losses.


Jurisdictional Estimates

The loss estimates using methods 1 and 2 above can only be performed county-wide. To derive the jurisdictional estimates, the existing (2007) and future (2035) population estimates can be used to apportion losses to each jurisdiction. The total population distribution by jurisdiction is shown on Table 5-41 below. (See Section 5.6.2 "Inventory Methodology"). The damage estimates presented in this section, however only apply to existing conditions.

Table 5-41. Population Distribution by Jurisdiction

Jurisdiction

Estimated 2007

% of 2007 Estimate

Projected 2025

% of 2025 Projection

Marshall County

87,644

100.0%

111,385

100.0%

Albertville

19,536

22.3%

26,658

23.9%

Arab

7,691

8.8%

9,590

8.6%

Boaz

8,213

9.4%

10,112

9.1%

Douglas

579

0.7%

816

0.7%

Grant

689

0.8%

689

0.6%

Guntersville

8,267

9.4%

9,929

8.9%

Union Grove

98

0.1%

98

0.1%

Unincorporated

42,571

48.6%

53,492

48.0%

HAZUS-MH Flood, Earthquake, and Hurricane studies were performed for Marshall County as the planning region. Global Reports of the HAZUS-MH runs contain detailed reports of the results. These studies, maps, and reports were prepared by an qualified GIS professional with advanced HAZUS training classes completed at the FEMA Emergency Management Institute in Emmitsburg, Maryland and extensive experience in its local application to mitigation planning. Each of these Global Reports contains more detailed results. These detailed reports are maintained on file by the Marshall County EMA and are available for public review:

  1. HAZUS-MH 100-Year Flood Event Global Report, dated April 29, 2009
  2. HAZUS-MH 500-Year Flood Event Global Report, dated April 9, 2009
  3. HAZUS-MH 500-Year/6.5 Magnitude Earthquake Event Global Report, dated March 31, 2009 (reports of lesser frequencies and magnitudes showed little or no damages)
  4. HAZUS-MH 1916 Irondale Earthquake Global Report, dated March 31, 2009
  5. HAZUS-MH Probabilistic 50-Year Hurricane Report, dated April 13, 2009
  6. HAZUS-MH Hurricane Opal Global Report, dated April 13, 2009

Flood Loss Estimates

Two flood event scenarios were assessed with HAZUS-MH: the 100-year and 500 year events. Summaries of the results are presented in this Plan.

The following table compares the overall "Quick Assessment" results from the 100-year and 500-year flood events. All other HAZUS loss estimates reported in this section are based on the 100-year flood event. The 500 year flood loss estimate is approximately 17% higher than the 100 year event.

Table 5-42. HAZUS-MH Flood Module Quick Assessment Results

Study Region:

Marshall County

Marshall County

Scenario:

100 Year Flood Event

500 Year Flood Event

Area (Square Miles)

567

567

Number of Residential Buildings

38,504

38,504

Number of All Buildings

41,651

41,651

Number of Persons in the Region

82,000

82,000

Residential Building Exposure ($ millions)

$3,707

$3,707

Total Building Exposure ($ millions)

$5,269

$5,269

Displaced Population (# of households)

449

495

Short Term Shelter Requirements (# of people)

420

506

Residential Property (Capital Stock) Losses

($ millions)

$27.14

$31.55

Total Property (Capital Stock) Losses ($ millions)

$42.98

$50.02

Business Interruptions (Income) Losses ($ millions)

$0.41

$0.53

Total Economic Losses ($ millions)

$70.53

$82.10

Economic Losses by Jurisdiction. A general total economic loss estimate can be obtained by applying the 2007 population apportionment for each jurisdiction to the total county-wide economic losses, as shown in the following table.

Table 5-43. Total Economic Losses by Jurisdiction

Jurisdiction

Apportionment of Losses

Total Economic Losses

($ millions)

Marshall County

100.00%

$70.53

Albertville

22.30%

$15.73

Arab

8.80%

$6.21

Boaz

9.40%

$6.63

Douglas

0.70%

$0.49

Grant

0.80%

$0.56

Guntersville

9.40%

$6.63

Union Grove

0.10%

$0.07

Unincorporated

48.60%

$34.28

Building Related Damages. HAZUS estimates that about 113 buildings would be at least moderately damaged from the 100-year flood event. This represents over 24% of the estimated number of buildings at risk of flooding in Marshall County. An estimated 16 homes (14 manufactured homes) would be completely destroyed. Of the remaining 97 damaged buildings, 96 are wood frame construction. Table 5-44 "Exposure of Buildings to 100 Year Flood" shows the exposure of buildings to the 100 year flood event. Table 5-45. "Building Related Losses, 100 Year Flood" breaks down in detail the estimated losses to the buildings, contents, and inventory, as well as losses due to interruptions in use of the buildings. GIS maps, which follow, depict the location of the HAZUS-generated flood and building damages and exposure to flooding.

Essential Facilities Damages. HAZUS shows no damages to the 65 essential facilities (police stations, fire stations, hospitals, and schools) in Marshall County.


Table 5-44. Exposure of Buildings to 100 Year Flood

Occupancy

Value of All Buildings ($1,000)

Flood Exposure ($1,000)

% of All Buildings

Agriculture

$26,365

$5,570

21.13%

Commercial

$933,683

$107,510

11.51%

Education

$54,756

$5,901

10.78%

Government

$37,537

$8,274

22.04%

Industrial

$390,787

$28,020

7.17%

Religion

$118,651

$21,087

17.77%

Residential

$3,707,199

$800,451

21.59%

Total

$5,268,978

$976,813

18.54%

Table 5-45. Building Related Losses, 100 Year Flood

Occupancy

Building Damage
($ millions)

Subtotal Building Damage

Interruption Losses ($ millions)

Subtotal Interruption Losses

Total Loss

Building Damage

Contents Damage

Inventory Loss

Income Loss

Relocation

Wage Losses

Rental Income Loss

Residential

$17.08

$10.06

$0.00

$27.14

$0.00

$0.03

$0.01

$0.01

$0.05

$27.19

Commercial

$2.18

$6.58

$0.13

$8.89

$0.05

$0.01

$0.00

$0.05

$0.11

$9.00

Industrial

$1.03

$2.56

$0.57

$4.16

$0.00

$0.00

$0.00

$0.00

$0.00

$4.16

Other

$0.48

$2.29

$0.02

$2.80

$0.00

$0.00

$0.00

$0.25

$0.25

$3.05

TOTAL

$20.78

$21.48

$0.73

$42.98

$0.05

$0.04

$0.01

$0.31

$0.41

$43.39

Map 5-45. Total Building Damages

Map 5-46. Total Residential Building Damage

Map 5-47. Value of Buildings Exposed to Flooding

Earthquake Loss Estimates

HAZUS-MH was used to assess various earthquake scenarios. Two probabilistic scenarios included the 100 year, 5.0 magnitude earthquake and the 500 year, 6.5 magnitude earthquake. The 100 year event showed no damage whatsoever, and the 500 year event showed only some damage. Next, a historical event, the 1916 Irondale earthquake near Birmingham, was assessed. This event was a 5.1 magnitude earthquake, Alabama's earthquake of record that had far reaching ground shaking effects that included Marshall County. The 1916 event provides the most meaningful results, which are presented in this Plan.

The GIS maps on the following pages were generated through HAZUS-MH and show slight variations in ground shaking and minor economic losses (by Census tract) resulting from the 1916 earthquake.


Map 5-48. 1916 Irondale Earthquake Ground Shaking Impacts


Map 5-49. 1916 Irondale Earthquake Economic Loss Impacts

Hurricane Loss Estimates

Two hurricane events were assessed by HAZUS-MH: a 50 year probabilistic scenario and the 1995 Hurricane Opal historical event. Hurricane Opal had damaging wind and flooding effects throughout Alabama, however, HAZUS only assesses the wind effects.

Economic Losses. The Hurricane Opal assessment reports only minor building damage resulting from peak wind gusts of 64 mph. HAZUS reports a total of $510,000 in building and related damage and no damage to essential facilities. In contrast, the 50 year event losses would total $222,000 to 9 buildings. According to the HAZUS analysis, the lower probability hurricane events with a return period of 500 years or longer could have significant impacts on Marshall County, as demonstrated on the following table. The table also shows the average annual loss of $147,000 that can be expected from a Marshall County hurricane event.

Table 5-46. Hurricane Economic Losses

Frequency of Hurricane Event (Years)

Residential Damage ($1,000)

Total Building Damage ($1,000)

Business Interruption Losses ($1,000)

Total Economic Losses ($1,000)

10

$0

$0

$0

$0

20

$0

$0

$0

$0

50

$213

$222

$0

$222

100

$1,758

$1,927

$1

$1,928

200

$5,023

$5,417

$268

$5,685

500

$11,898

$12,844

$1,012

$13,856

1000

$20,113

$22,671

$2,131

$24,802

Annualized Losses

$114

$133

$14

$147

The GIS map on the following page was generated by HAZUS and shows the distribution by Census tract of minor economic losses from Hurricane Opal.


Map 5-50. Hurricane Opal Direct Economic Losses


5.7.4 Loss Estimates Based on Historical Records

Tornado Loss Estimates

According to the NOAA National Climatic Data Center and National Weather Service (NWS) records (see Appendix E "Hazard Profile Data" and Section 5.4.1 "Tornadoes Profile"), Marshall County has the following historical averages for the 52-year period spanning 1957 through 2008:

The results of these records are summarized in the following table, which shows the economic loss estimates for tornadoes. The next table shows the apportionment of these loss estimates among the Marshall County jurisdictions.

Table 5-47. Annual Economic Losses due to Tornadoes

 

Total for Period

Annual Estimate

Period

1957 - 1958

-

Years

52

-

Events

38

0.73

Deaths

13

0.25

Injuries

344

6.62

Cost of deaths ($ millions)

$28.60

$0.55

Cost of injuries ($ millions)

$4.30

$0.08

Property damage ($ millions)

$24.56

$0.47

Total economic losses

$57.46

$1.11

Table 5-48. Tornado Loss Estimates by Jurisdiction

Jurisdiction

Apportionment of Losses

1957-1958 Economic Losses ($ millions)

Annualized Economic Losses ($ millions)

Marshall County

100.00%

$57.46

$1.11

Albertville

22.30%

$12.81

$0.25

Arab

8.80%

$5.06

$0.10

Boaz

9.40%

$5.40

$0.10

Douglas

0.70%

$0.40

$0.01

Grant

0.80%

$0.46

$0.01

Guntersville

9.40%

$5.40

$0.10

Union Grove

0.10%

$0.06

$0.00

Unincorporated

48.60%

$27.93

$0.54

Severe Storm Loss Estimates

Historical damages for severe storms in Marshall County are not available. Damage records maintained by NOAA include multiple counties, and no other source is available. The 2007 Alabama State Hazard Mitigation Plan did not include severe storms in its loss estimates.

Flood Loss Estimates

NOAA records (see Appendix E) report frequent flooding over the period since 1997. These records show 21 floods over the 12 year period or almost two per year. NOAA estimates are low and show only minor damages; this conflicts with local news media reports of flooding, which indicate frequent flooding of buildings, roads, and bridges. The total damages for the 21 events are estimated at $517,000 or $47,000 per year.

Other available flood loss data can be obtained from National Flood Insurance Program (NFIP) claims. As of 1/31/09, there were 68 policies with over $14 million of flood insurance in force. Most of those policies (42 of 68) were for properties within unincorporated Marshall County, the area most at risk for flooding. There have only been seven flood insurance claims since 1978 totaling $228,307. Three of these claims were in unincorporated areas and three were in the City of Albertville.

The historical flood damage date is insufficient as a basis for flood loss estimates for this Plan.


Loss Estimates for Remaining Hazards

Historical data is not available to estimate losses from the remaining hazards identified in this Plan. In some cases, there have been no recorded events, such as dam/levee failures, and in other cases, no damages resulted from an event, such as instances of landslides and sinkholes.

5.7.5 Recommended Risk Assessment Measures

The Mitigation Strategy of this Plan should include both short term and long term measures to improve the completeness and reliability of loss estimates. These measures should carry out the following general objectives:

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5.8 General Description of Land Uses and Development Trends

Impacts of Development Trends on Vulnerability

A county's development trends demand consideration in any effective plan for hazard mitigation. It is crucial to continually monitor and analyze development trends, as new land use patterns and centers of economic activity can impact jurisdictions' vulnerabilities and change the exposure of shifting populations, new structures, and enlarged infrastructure to natural hazards. An area's course of development is dynamic and carries with it risks to valuable property and citizens' lives. This section examines the projected growth trends for Marshall County that should affect the location and impact of vulnerability to natural hazards in coming years. The potential impacts of these changes can have adverse impacts, such as those noted here:

Population Growth

The 2000 census recorded 82,231 residents of Marshall County. This number represents a 16% increase between 1990 and 2000. From 2000 to 2007, projections point to a slower rate of growth of 7% but one that is still 2.9% faster than the state's rate of growth, as shown on the following table.

Table 5-49. 1990 - 2007 Population Growth

Population Change from 1990 to 2007

Jurisdiction

1990

2000

Number Change

Percent Change

2007

Number Change

Percent Change

Alabama

4,040,587

4,447,100

406,513

10.1%

4,627,851

180,751

4.1%

Marshall Co.

70,832

82,231

11,399

16%

87,644

5,413

7%

Albertville

14,507

17,247

2740

19%

19,536

2,289

13%

Arab

6,321

7,174

826

13%

7,691

517

7%

Boaz

6,928

7,411

483

7%

8,213

802

11%

Douglas

474

530

56

12%

579

49

9%

Grant

638

665

27

4%

689

24

4%

Guntersville

7,038

7,395

357

5%

8,267

872

12%

Union Grove

119

94

-62

-40%

98

4

4%

Source: Census Bureau

As shown above in Table 5-49., growth within Marshall County has centered on Albertville, which is the largest city in Marshall County. Guntersville, Boaz, and Arab also showed significant growth. The following maps illustrate growth patterns in Marshall County in recent years.

Map 5-51. 2007 Population Distribution

Map 5-52. Population Density Changes

Map 5-53. Distribution of Population Increases


Future estimates show moderate growth continuing in Marshall County. The population should increase by 29,154 residents, or 35.5%, between 2000 and 2025. This growth is somewhat faster than the estimates for the state of Alabama, but not fast enough to raise major concerns over changes in land use and population density.

Table 5-50. 2025 Projected Population


Projected Population Growth 2000-2025

 

2000

2005

2010

2015

2020

2025

#

%

Alabama

4,447,100

4,644,503

4,838,812

5,028,045

5,211,248

5,385,997

938,897

21.1%

Marshall County

82,231

88,256

94,319

100,304

106,064

111,385

29,154

35.5%

Source: University of Alabama Center for Business and Economic Research

Factors Influencing Future Growth

Because of Guntersville Lake, Marshall County has emerged as a center for recreation and retirement. In the future, as the US population ages and the Baby Boomer generation retires, the Guntersville Lake area can be expected to develop to suit retirees' preferences for lakeside property.

In addition, to the north, Madison County is considered a high growth corridor, because of the tech industries centered in Huntsville and Redstone Arsenal. As population and income rise in Madison County, northern parts of Marshall County may experience corresponding growth in housing for workers who prefer to live in rural areas and commute to Huntsville. The county's scenic nature should also attract development of vacation homes for workers, especially around Guntersville Lake.

Industrial expansion is projected for all of Northern Alabama. The City of Boaz has been the site of new plants that supply parts for the nearby Honda automotive plant. The major source of industrial employment is poultry processing plants on Sand Mountain. Albertville features four industrial parks and markets itself aggressively to manufacturers.

Land Use Patterns

Most of Marshall County is agricultural. The area around the lake and river features pine forest used for recreation and timber.

Marshall County features a development pattern that is unusually dense for Alabama's agricultural counties. Roughly half of Marshal County's residents live in incorporated jurisdictions. The major population center is in lower Marshall County around Albertville and Boaz, on top of Sand Mountain. The other population concentration is around Guntersville Lake and the Tennessee River. The maps on the following pages describe existing land use for Marshall County.

Map 5-54. Land Use and Land Cover

Map 5-55. Guntersville Land Use

Map 5-56 . Albertville Zoning

Map 5-57. Arab Land Use


Impacts of Hazards of the Location of Growth and Development

The major hazards affecting Marshall County are tornadoes and severe storms. These are general hazards that do not affect particular jurisdictions within the county. Therefore, efforts to mitigate tornadoes and severe storms should be addressed with county-wide efforts and do not have to affect development patterns within Marshall County. Wildfires pose another county-wide threat.

The location-specific hazards relevant to development within Marshall County are landslides on the slopes of Sand Mountain. Future planning should seek to mitigate the risks of development around Sand Mountain.

Although Marshall County features residential development around its waterways, flooding is not a serious concern. TVA dams control the water levels for Guntersville Lake and can adjust for severe rainfall. Albertville, Boaz, and Arab lie outside of the 100 and 500 year frequency dam failure inundation areas for Guntersville and Nickajack dams. However, development from the Huntsville metropolitan area in Madison County could occur in northwest Marshall County, within the inundation area for the Guntersville dam.

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5.9 Repetitively-Damaged NFIP-Insured Structures

According to the Alabama State NFIP (National Flood Insurance Program) Coordinator, Marshall County communities have no repetitive loss structures within their jurisdictions, as of April, 2009. This could be explained by the relatively few policies in effect and small number of losses. As shown on the following table, there are 68 NFIP policies in effect within Marshall County communities totaling $14,200,800 in coverage and $43,970 in premiums. As shown on the next table, there have been seven flood insurance claims since 1978 totaling $228,307.

Table 5-51. NFIP Policies as of 1/31/09

Community Name

Policies in Force

Insurance in Force

Written Premium in Force

ALBERTVILLE, CITY OF

5

$899,100

$2,787

ARAB, CITY OF

7

$1,315,800

$4,575

BOAZ, CITY OF

1

$75,900

$722

GUNTERSVILLE, CITY OF

12

$2,680,000

$14,744

MARSHALL COUNTY

43

$9,230,000

$21,142

ALL

68

$14,200,800

$43,970

Total for Alabama

55,151

$10,647,429,000

$33,297,906

Source: NFIP Statistics Report at http://bsa.nfipstat.com/reports/reports.htm

Table 5-53. Jurisdictional Risk Variations

Community Name

Total Losses

Total Payments

ALBERTVILLE, CITY OF

3

$65,500

ARAB, CITY OF

1

$92,461

MARSHALL COUNTY

3

$70,346

ALL

7

$228,307

Total for Alabama

36,040

$926,650,675

Source: NFIP Statistics Report at http://bsa.nfipstat.com/reports/reports.htm

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5.10 — Risks that Vary Among the Jurisdictions

This Plan has strongly emphasized the variations in risks among jurisdictions throughout all components of this Risk Assessment. In particular, the following sections of the Risk Assessment contain specific references to jurisdictional variations:

Table 5-53 "Jurisdictional Risk Variations" presents an overview of the common and unique risks within each jurisdiction and the unique characteristics of those risks.

The projected county-wide growth rate from 2007 to 2025 is 27%, with rates going as high as 36% in Albertville. Most growth is projected within incorporated areas. Occupancy of buildings by jurisdiction is assumed to generally follow the same county-wide allocation, and is projected to change according to each jurisdiction's growth multiplier. The primary occupancy classification is residential, with most homes located within the City of Albertville. All buildings are equally exposed to the two most severe hazards - tornadoes and severe storms - regardless of jurisdiction.

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