Hazard Identification and Risk Assessment
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Santa Rosa County Local Mitigation Strategy SECTION 3 HAZARD IDENTIFICATION AND RISK ASSESSMENT 3.1 Santa Rosa County Local Mitigation Strategy This page intentionally left blank. 3.2 Santa Rosa County Local Mitigation Strategy HAZARD IDENTIFICATION AND RISK ASSESSMENT Introduction This section of the Santa Rosa County LMS summarizes the results of a hazards and vulnerability assessment process undertaken by the Task Force members and includes a description of the types of natural hazards that may affect Santa Rosa County, their probability of occurrence, the geographic locations that are vulnerable, the number of structures and population affected, and potential loss estimates. This information, gathered from a variety of sources, provides the best available data for describing and quantifying the potential impacts to Santa Rosa County and is consistent with the County’s Hazard Identification and Risk Assessment (HIRA). Primary attention is given to natural hazards considered reasonably possible to occur in the County as identified through research by staff, input from members and citizens, and data provided by FEMA and other sources. These hazards include: Flooding (Hurricanes, Tropical Storms, and Thunderstorms) Severe Storms and Lightning (Including Hurricane Winds) Tornadoes and Waterspouts Wildfire Heat Waves and Drought Winter Storms and Freezes Erosion Tsunamis/Rogue Waves This update of the LMS omits natural hazards which were discussed in prior versions that are unlikely to occur in Santa Rosa County. Those natural hazards are earthquakes, avalanches, land subsidence, landslides, volcanos, and sinkholes. The reasons for omission are listed below: • Earthquakes – The US Geological Survey National Seismic Hazard Mapping Project concludes there is minimal risk of an earthquake occurring within Santa Rosa County. While small seismic activity cannot be ruled out due to the Pollard-Foshee fault located around Conecuh, Alabama, the rarity and lack of damages from such events warrant no additional attention from the Local Mitigation Strategy Task Force at this time. • Avalanches – Santa Rosa County does not receive adequate amounts of snow to warrant concern regarding avalanches. Likewise, the topography of Northwest Florida does not lend itself to this hazard. • Land subsidence – Land subsidence typically occurs when large amounts of groundwater have been withdrawn from rocks, such as fine-grain sediments. Santa Rosa County’s aquifers are sand and gravel and are recharged by rainfall and groundwater recharge. There are also pumping limits in place by municipal water suppliers to ensure aquifers are not overdrawn. Thus, the lack of 3.3 Santa Rosa County Local Mitigation Strategy groundwater quantity issues significantly reduces the likelihood of subsidence from occurring within the county. • Landslides - According to NASA’s Global View of Landslide Susceptibility application, the Santa Rosa County area ranks in the lowest level risk category only having a slight risk of landslides. The reason for this determination is that steep slopes are the most important factor that make a landscape susceptible to landslides. Other key factors include deforestation, the presence of roads, the strength of bedrock and soils, and the location of faults. Because Santa Rosa County has minimal variation in topography, landslides are not a common issue for the residents of Santa Rosa County. • Volcano – The closest known volcano in the United Stated is the Carrizozo lava flow in New Mexico, which is located more than 1,800 miles from Santa Rosa County. • Sinkholes – While the entire state of Florida is technically susceptible to sinkholes, the information noted above regarding land subsidence is likewise relevant to this hazard. Additionally, FL Dept. of Environmental Protection reports no cases of sinkholes/subsidence having occurred within Santa Rosa County. Should any omitted or unidentified natural hazards become prevalent within Santa Rosa County, the LMS Task Force shall consider the additional of such hazards to this plan. During a previous LMS update dam/levee failure was identified as a separate hazard; however, the dams in Santa Rosa County are fairly small and impacts from failures fall within the broader hazard category of flooding. The Task Force discussed adding other man-made or technological hazards in the previous update and decided to keep the LMS focus on natural hazards. Only Natural hazards are addressed in detail in the LMS. The Santa Rosa County HIRA is the guiding document for identifying and assessing natural and human-caused hazards for planning, response, recovery, and mitigation activities. Human caused hazards are addressed in detail in the Comprehensive Emergency Management Plan (CEMP) Mitigation Element. General Description of Santa Rosa County Santa Rosa County is located in northwest Florida bordering the Gulf of Mexico and Santa Rosa Sound. The County is bounded on the west by Escambia County, on the east by Okaloosa County and on the north by Escambia County, Alabama. The total area of Santa Rosa County is approximately 751,000 acres, including land and water. Almost 34% of the county consists of military reservation lands and conservation lands (Eglin Air Force Base comprises 8.8%, Naval Air Station Whiting Field and NOLFs comprise almost 1%, and Blackwater River State Forest comprises approximately 20% of the total county land area). The county’s three municipalities comprise only about 1% of the entire county area. The unincorporated area of Santa Rosa County (including 3.4 Santa Rosa County Local Mitigation Strategy Eglin Air Force Base, Naval Air Station (NAS) Whiting Field and Blackwater State Forest) comprises approximately 639,914 acres, most of which is rural in nature (see Map 3-1 – General Location Map). TOPOGRAPHIC FEATURES Santa Rosa County lies within the Coastal Plain, a broad belt consisting primarily of unconsolidated sands, silts and clay. The County is divided into two physiographic divisions, the Western Highlands and the Gulf Coastal Lowlands. Most of the County is located in the Western Highlands, which is a southwardly sloping plateau whose surface has been cut by numerous streams. The three principal streams that drain this area are the Escambia, Blackwater and Yellow Rivers. The many smaller streams that feed these rivers have a trellis drainage pattern and commonly head in small steep sided box canyons known as steepheads. Steepheads form where undermining by springs create steep slopes at the head of smaller streams. Several faults in the northern part of the County, where elevation ranges from 100 to 290 feet above sea level, form steep hills. The Gulf Coastal Lowlands is the low-lying area of southern Santa Rosa County. The Lowlands are a series of parallel terraces consisting of relatively undissected, nearly level plains rising from the coast in successively higher levels. Dunes, barrier islands, beach ridges, and other topographical features were stranded inland as seas receded. The highest terrace has an elevation of about 100 feet. The southern boundary of the Gulf Coastal Lowlands is formed by Santa Rosa Island, which is approximately 50 miles long and varying between approximately 1,000 and 1,500 feet wide and crosses not only Santa Rosa County but also Escambia County to the west and Okaloosa County to the east. SURFACE WATER RESOURCES Santa Rosa County has as rich diversity of unique coastal resources as well as a significant amount of water resources including the Blackwater River which is an Outstanding Florida Water, the Escambia River, the Yellow River, the East River, Escambia Bay, Blackwater Bay and East Bay, Santa Rosa Sound as well as the Gulf of Mexico. These major waterways in addition to other tributaries have been identified as major drainage features in Map 3-2. SIGNIFICANT HABITATS Santa Rosa Island is the only barrier island within Santa Rosa County. These pristine white sands provide a valuable environmental and economic stimulus to the county. Upland forest, mixed coniferous/hardwoods, cropland and pastureland, shrub and brushland as well as coastal scrub and beaches are the predominant communities which provide resources for habitat within the county. Managed lands include a large portion of the county. Eglin Air Force Base and NAS Whiting Field provide a large military presence in the community and both agencies cooperate with the county through mutual aid agreements in support of hazardous and emergency conditions. Map 3-3 portrays the locations of these managed lands as well as sea grass beds which provide habitat for vital marine resources. 3.5 Santa Rosa County Local Mitigation Strategy CLIMATE Local temperatures and their seasonal changes reflect climatic conditions characteristic of the northwest Florida. Santa Rosa County has borderline subtropical temperatures with rare, short duration freezing events affecting the County during late December through March. Historical records for Santa Rosa County from the NOAA National Center for Environmental Information indicate the 1981-2010 Climate Normals are NCDC's latest three-decade averages of climatological variables, including temperature and precipitation. This new product replaces the 1971-2000 Climate Normals product, which remains available as historical data. The average minimum winter temperature is 42’ Fahrenheit. The average maximum summer temperature is 92’. Average participation is 65.27 inches. Winter temperatures are cool enough to give a pronounced seasonal character to plant growth.