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Floodplains <br />Large portions of Indian River County are subject to flooding. Among the factors contributing to <br />this are the relatively low flat topography, the absence of natural drainage systems, and the <br />relatively high annual rainfall. <br />Within the county, there are two ridges that parallel the coast and are remnants of offshore bars. <br />The easternmost ridge is known as the Atlantic Coastal Ridge and is approximately % mile to 1 <br />mile west of the Indian River Lagoon. This ridge has a maximum height of approximately 54 <br />feet, but several places along the ridge have been reduced in elevation due to excavation <br />associated with development. The second ridge is known locally as the Ten Mile Ridge and <br />closely follows the I-95 corridor. That ridge is older than the Atlantic Coastal Ridge and has a <br />maximum height of approximately 35 feet. Between the ridges lies a flat shallow depression that <br />is a natural drainage basin that historically drained to the south prong of the St. Sebastian River. <br />Today, the southern end of that basin is covered by a network of drainage canals which outfall to <br />the Indian River Lagoon, and only a small portion of the basin in the north part of the county still <br />drains to the St. Sebastian River. <br />West of I-95, the topography of the county is relatively flat, with a rise in elevation near the <br />Indian River County/Osceola County line. The area between this rise and I-95 is marshy and <br />poorly drained, with some drainage improvements having been made to benefit area citrus <br />groves, cattle ranches and other agricultural interests. A large portion of western Indian River <br />County is covered by the St. Johns Marsh. The marsh flows north to form the St. Johns River. <br />Two sources of flooding in the county are tropical storms and hurricanes. The flooding that is <br />associated with those storms presents the greatest potential loss of life and property. In coastal <br />areas, storm surges and tides up to 15 feet above sea level can occur in association with hurricane <br />storm events. <br />Those areas of the county which are subject to flooding are identified on Figure 2.23. <br />Future Land Use Element 57 <br />