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4 . 1 NATURAL HAZARDS <br /> Indian River County is susceptible to a number of natural hazards with the <br /> potential to cause extensive damage within the community . The cost of responding to and <br /> recovering from these disasters has proven to be significant . Planning for these events <br /> before they occur can significantly reduce costs in the future . This subsection w II now <br /> identify those hazards in Indian River County identified as being naturally occurr ng . <br /> 4al A Flooding <br /> 4. 1 . 9 . 1 Hazard Identification <br /> In Indian River County, several variations of flood hazards occur due to the <br /> different effects of severe thunderstorms , hurricanes , seasonal rains , and other <br /> weather- related conditions . For the majority of the County , the primary causes of flooding <br /> are hurricanes or tropical storms . However, the County's low-lying topography , combined <br /> with its subtropical climate , make it vulnerable to riverine as well as storm -associated <br /> flooding . <br /> Flooding in Indian River County results from one or a combination of both of the <br /> following meteorological events : <br /> 1 ) Tidal surge associated with northeasters , hurricanes , and tropica storms ; and <br /> 2 ) Overflow from streams and swamps associated with rain runoff. <br /> When intense rainfall events occur, streams and drainage ditches tend to reach <br /> peak flood flow concurrently with tidal water conditions associated with coastal storm surge . <br /> This greatly increases the probability of flooding in the low-lying areas of the coastal zone . <br /> Areas along the Indian River are particularly susceptible to flooding under, these conditions . <br /> The most flood prone areas in the eastern portion of the County feature poorly drained soils , <br /> a high water table , and relatively flat terrain , all of which contribute to their flooding <br /> problems . Flat terrain and heavily wooded areas aggravate flood problems by preventing <br /> rapid drainage in some areas . <br /> Riverine flooding occurs when the flow of rainwater runoff exceeds the carrying <br /> capacities of the natural drainage systems . During extended periods of heavy rainfall , <br /> certain low-lying neighborhoods within the County are subject to considerable flood damage <br /> and isolation caused by the inability of natural and mechanical drainage systems to <br /> effectively remove the water. Heavy rainfalls can cause considerable damage t County <br /> infrastructure including roadbeds , bridges , drainage systems , and the water supply. <br /> The buildup of uncontrolled sediment contributes to the problem of inadequate <br /> drainage in natural and mechanical drainage systems . When a storm produces an <br /> overwhelming amount of stormwater runoff, the accumulation of loose sediment causes <br /> flooding by clogging the drainage systems . This buildup of sediment in Indian River County <br /> waterways has lead to the degradation of the national estuary . The County is currently <br /> working to address this issue by replacing bottom opening radial gates with tilting gates at <br /> four water control structures . <br /> Long -term climate monitoring stations indicate that rainfall in Indian River County <br /> averages about 51 . 5 inches annually , with about half of this volume occurring during the <br /> 4-6 <br />