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TO: Honorable Board of County DATE: November 10, 1981 FILE: Comm, issioners ;.�0tf 1n8i �J1 SUBJECT: WAVE HEIGHT ANALYSIS & NEW FIRMS Nclk��9qeZ tVI FROM. Neil Nelson RE;: ERENCES: County Administrator It is recor-mended that the data herein presented be given formal consideration by the County Commission.. DESCRIPTION & CONDITIONS: -- The purpose of the titirave Height Analysis is to revise the Flood Insurance Rate Maps (FIK1) in the -unincorporated -areas of Indian River County to include the effects of wave action associated with flooding from the Atlantic Ocean at the open coast and at Indian River and Sebastian Creek. Previously, FIRI•Is were produced showing only the stillwater storm - surge elevations due to the lack of a suitable and generally applicable methodology for estimating the wave crest elevations associated with storm surges. These stillwater elevations were subsequently stipulated in community flood plain management ordinances as the minimum elevation of the first floor of new construction. Co-"munities and individuals had to consider the additional hazards of velocity waters and wave action on an ad hoc basis. Because there has been a pronounced tendency for buildings .to be constructed only to meet minimum standards, without consideration of the additional hazard due to wave height, increasing numbers of people could unknowingly be accepting a high degree of flood -related personal and property risk in coastal areas subject to wave action. Therefore, the Federal Emergency Management Agency has pursued the development of a suitable methodology for esti- mating the wave crest elevations associated with storm surges. The recent development of such a methodology by the National Academy of Sciences has led to the adoption of wave crest elevations for use as the base flood elevations in coastal communities. The stillwater elevations developed used as the starting elevations for herein. ALTERNATIVES AND ANALYSIS: for these previous studies were the wave height analysis presented The data in the Wave Height Analysis report is authoritative for the purposes of the National Flood Insurance Program and data presented in that report supersede all previous flood elevation determinations. Wave heights were computed along transects which were located along the coastline as shown in Figure l on the report. Each transect was taken perpendicular to the shoreline and extended to the inland limit of tidal flooding. Along each transect, wave heights and elevation= were computed considering the combined effects of charges in g- 1 -cu -elevation, vegetation, and physical features. The stillwater ele- for the 100 -year flood were used as the starting elevations for t. computations. Wave heights were calculated to the nearest 0.1 fooar, and wave elevations were determined at whole -foot increments along the transects. The location of wave heights of approximately 6 fee=, NOV 181981 5 t'�GK 3 F;, r7136