2016-069V - Laserfiche WebLink

Home Browse Search

The Palmer Drought Index has become the semi-official drought index. It is most effective in determining long term drought—a matter of several months—and is not as good with short-term forecasts (a matter of weeks). It uses a 0 as normal, and drought is shown in terms of minus numbers; for example, minus 2 is moderate drought, minus 3 is severe drought, and minus 4 is extreme drought. The Palmer Index can also reflect excess rain using a corresponding level reflected by plus figures; i.e., 0 is normal, plus 2 is moderate rainfall, etc. Another reference tool is the Keetch-Byram drought index (KBDI), which is a continuous reference scale for estimating the dryness of the soil and duff layers. The index increases for each day without rain (the amount of increase depends on the daily high temperature) and decreases when it rains. The scale ranges from 0 (no moisture deficit) to 800 (prime drought condition). The range of the index is determined by assuming that there is 8 inches of moisture in a saturated soil that is readily available to the vegetation. In November, 2009, the lack of rainfall during rainy season led to Indian River County being named the driest county in the state of Florida and, according to the Florida Florida Forest Service, in danger of wildfires. According to the Keetch Bryam Drought Index, the county measured in at 649 when the normal range for that time of year is 271-420. Indian River County could reasonably expect to see a drought index of this magnitude. k. Seismic Hazards (Dam/Levee Failure) – Hazard Identification. Dam/levee failure poses a minor threat to population and property in Indian River County. All dams and levees are earthen structures and are State, regional, local, or privately controlled. The most significant risk related to dam/levee failure is flooding due to substantial rainfall and its eastward migration to final discharge in the Indian River Lagoon. Structural and non-structural techniques to slow and contain this runoff incorporate several drainage systems. Rainfall in excess of designed capacities could cause erosion of constructed drainage facilities and flooding of many areas including primary roadway evacuation routes (Indian River County Emergency Management, 2002). According to the National Inventory of Dams, there are five listed dams in Indian River County (South Relief Structure, Lateral C Structure, Main Canal Structure, North Relief Canal Structure, Lateral Indian River County Comprehensive Emergency Management Plan Basic Page 49