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and planning for open space around existing and proposed structures to allow for the passage of debris and flood \vaters. San Diego County, California, has adopted (by reference from a 1981 FEMA report) recommended management tools for various development scenarios on alluvial fans. The county uses a matrix that relates the hydraulic zone to the existing density level and the projected density level to determine which type of flood protection measure is appropriate. (See Figure 4-5.) SPECIAL CONSIDERATIONS IN COASTAL HIGH-HAZARD AREAS Coastal flooding results from storm surge (the rise in the ,vater surface due to barometric pressure and the piling up of \vater as a result of wind). \^/ave impacts, particularly ,vave set-up and wave run-up, can cause damage. (Wave set-up, according to FEMA, is the "super elevation of the water surface over normal surge elevation." Wave run-up is the action of a wave after it breaks and the water "runs-up" the shoreline or other obstacle, flooding areas not reached in the initial storm surge.) Damage to natural and man-made features occurs through the sheer pressure of the water as well as by battering solid objects against one another and scouring sand from underneath foundations (Federal Interagency Floodplain Management Task Force 1992). In many areas of the coast, coastal erosion also poses a significant hazard. Coastal erosion can directly damage buildings or increase storm hazards by eroding a\vay natural protective features. NFlI' minimum requirements do not directly address coastal erosion, but many states and communities have established coastal erosion management programs. Development in coastal areas, as in riverine areas, increases the frequency and severity of flooding v",hen it interrupts natural topography (especially protective dunes), disturbs natural drainage patterns, and leads to the removal of natural vegetation that would othenvise absorb water and reduce \-vave impacts. Filling in coastal \vetlands and estuaries to increase developable land exacerbates the flooding problem and threatens water quality and wildlife habitat in these regions. Furthermore, the construction of seawalls, groins, and jetties as a means of preventing flooding and controlling shoreline erosion \veakens the shoreline's natural protection system, is less effective in managing \-vind and ,vaves, and can also exacerbate flooding in adjoining properties. Soil permeability, ,vhich is important for natural percolation of water, is also reduced when sand is removed and dunes are leveled to accommodate buildings or roads. Coastal high-hazard areas are designated as V-zones on a Flood Insurance Rate Map. V-zones are defined as those portions of the coastal floodplains that are subject to high-velocity \vaters from waves during a 1 percent annual chance flood. The V-zone is usually determined by the area subject to wave heights of three feet or greater. Because of the unique hazards to structures located in V-zones, NFIP requires communities with these zones to adopt regulations that provide for the following. . New construction must be landward of mean high tide. . Ne\v construction and substantial improvement to existing structures must be elevated on anchored pilings or columns so that the bottom of the Imvest horizontal structural member of the lo\vest floor is elevated to or above the base flood elevation. . Structures must be anchored to resist flotation, lateral movement, and collapse. . The space below the lmvest floor must be free from obstruction or constructed with a breaka,vav wall that will collapse under abnormally high tides or \vind-driven water V\rithout jeopardizing the main stnlcture. . The use of landfill for structural support is prohibited. . Human alteration of sand dunes and mangrove stands is prohibited if it would increase potential tlood damage. Eighteen coastal states and scores of local governments have established more stringent standards than those described above. Communities are encouraged to impose development restrictions and building requirements on development in the entire storm impact zone area that may be subject to all three forces of hurricane damage: storm surge, rainfall, and wind. This hurricane storm impact zone is a more extensive area that the coastal high-hazard zone (or V- zone) mapped under NFlP, which generally includes only lands immediately adjacent to the shoreline. The Army Corps of Engineers has been working with FEMA to provide communities with maps that delineate hurricane surge zones. The State of Florida Department of Environmental Protection established a coastal construction control line (CCCL) in the 19805 that defines a zone along the coastline that would be subject to flooding, erosion, and the wind impacts of a lOO-year storm. Today, all coastal counties and some municipalities in Florida (except Bay County) have enacted these more stringent rules. Coral Gables, Florida, for example, employs the strict standards applicable to coastal high-hazard areas farther inland than v\That is required by NFIP. The city also limits all residential structures to one story and has a 39-foot height limit for any structure or architectural feature in the coastal high-hazard zone. This restriction is credited with being instrumental in sparing the city from massive damage during Hurricane Andrew in 1992. Although there was some significant damage, very few single-family homes \""ere destroyed, unlike ,vhat happened in neighboring cities. REGULATIONS FOR DUNE AREAS Dunes are some of the most sensitive lands in the coastal zone. They protect inland areas from the ravages of \vind and waves. They are also attractive places to build homes given their proximity to the shoreline and ocean vie\vs. NFIP prohibits man-made 37