FLOOD04031 - Laserfiche WebLink

Home Browse Search

alteration of sand dunes and mangrove stands that \'.'ould increase the potential of flood damage. (See Sec. 60.3(e)(7)). Local governments often go beyond NFIP requirements for coastal high-hazard areas to increase protection of dunes and nearby residential development. Residential development on sand dunes creates problems, including destruction of vegetation and dune crests during construction of home and roads; pollution of surface and groundwater from on-site selvage disposal systems; and sand, wind, and storm damage to residential structures. Local dune regulations commonly include the following guidelines for development. (See also Figure 4-7.) . Residential development is allowed only inland of the active portion of the dunes. (Active dunes are those that are mobile or are in the process of gaining or losing sand.) Glynn County, Georgia, for example, requires that development in active dune areas be set back at least 40 feet land\vard of the crest of the most se,nvard stable dune. Figure 4-7. Typical Dune Cross Section t SHORELINE SAND STABILIZED J PRIMARY DUNE BY VEGETATION . Roads should be sited landward of the high dunes, in the trough behind the foredune, and through natural gaps in the dunes. Major subdivision roads should be parallel to dune ridges. Driveways and minor roads can be perpendicular to the dune but should not extend over the foredune ridge or other dune crests. Grasses can be planted in strips along the roads to capture sand and prevent it from blowing onto the roads. Some coastal states and communities have developed construction setback standards as part of their coastal zone management programs. Coastal setbacks are based on annual erosion rates and are intended to demark a seaward point of which development should not occur. These lines should be regarded as minimum setbacks- the farther a structure is setback from the ocean, the less storm damage \vill be sustained, regardless of the erosion rate. States that have coastal construction setbacks include California, \tVashington, Oregon, Maine, Massachusetts, Rhode Island, New York, Maryland, North Carolina, and Florida. Additionally, some communities require that all structures in the SECONDAIW DUNE VEGETATIONT PR01 ECTION HOUSE Coastal commrmities typically impose setbacks on residef/fial structures in dune areas, "lvhich limit col1stmcthm to points landlvard of primary and secondary dunes. Limits 0/1 public access, dune excavation, and removal of dune-stabilizing vegetation are also necessary to preserve the natural storm prevention and ecological functions of these fragile lands. . Excavation, flattening, and removal of sand from dunes, even temporarily during construction, is prohibited. . The foredune ridge-the dune closest to the beach- is to be left entirely clear of both residential structures and roads. . Residential lots should be configured in areas where vegetation has stabilized the dunes. (Active dunes are vegetated mostly \vith grasses; stabilized dunes generally have shrubs and woody vegetation.) . Only Imv-density residential development should be allo\ved in the troughs between the foredune and the high dunes, provided there is sufficient level space, or if structures are raised. If either condition cannot be met, development should be located behind the crestline and on the backslopes of the high dunes. 40 coastal zone have a freeboard elevation of at least one foot and as great as eight feet. At a minimum, states and communities usually require that all structures be placed landward of the primary dune. The North Carolina Coastal Area Management Act requires structures to be set back at least 30 times the annual erosion rate from the first line of dune vegetation. Erosion rates along the coast in Nags Head vary from two to nine feet per year. The Nags Head, North Carolina, subdivision ordi- nance requires lots on the ocean side of the major north- south road that parallels the coast to have an ocean-to- road configuration. (See Figure 4-8.) This allmvs for houses to be moved landward if and when coastal erosion threatens the structures. The ordinance also allows for a reduction in the required front-yard setback from the road from 30 feet to 15 feet as a means of accommodating structures that may have to be moved land"vard to avoid erosion.