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ORDINANCE NO. 87-19 <br />Rainfall Frequency Data <br />Vero Beach and Vicinity <br />Indian River County <br />Occurrence Duration Duration <br />10 5.5 inches 8.0 inches <br />25 6.4 inches 9.4 inches <br />100 8.0 inches 12.0 inches <br />The 10 -year 6 -hour storm is typically utilized as design <br />criteria for secondary drainage facilities such as storm sewers <br />and small ditches. The 25 -year 24-hour storm event is typically <br />used in Indian River County for design of primary drainage <br />systems. The 100 -year 24-hour event is commonly used for flood <br />insurance purposes under the National Flood Insurance Program. <br />Tides - Potential for flooding from storm surges and other <br />abnormally high tides exists along the County's coastal areas. <br />Storm surges up to 15 feet above mean sea level have been <br />associated with hurricanes. Coastal rivers <br />experience rises of five to seven feet during these periods. <br />Groundwater - The Anastasia Formation which is the shallow <br />aquifer underlying much of the County, consists of layers of sand, <br />shell, and clay. Below this layer lies the Hawthorne Formation <br />which is the impervious confining bed of the Anastasia Formation. <br />The Hawthorne formation is composed predominately of clay. Below <br />the Hawthorne Formation lies the Floridan Aquifer. The Hawthorne <br />Formation retards the upward movement of water from the Floridan <br />Aquifer. <br />Water from the Anastasia Formation is of good quality and is <br />the main source of supply for municipal and domestic use. Water <br />from the Floridan Aquifer is of poorer quality and is used <br />CODING: Words in ¢ttO¢X tXtO type are deletions from existing law. <br />Words underlined are additions. <br />