FLOOD06285 - Laserfiche WebLink

Home Browse Search

4 6. Periodic operation of the closure structure (at least once annually) is performed for testing and training purposes. 7. Sufficient documentation, indicating that each of the above requirements have been met, has been provided to, and accepted by, FlA. Mapping of Leveed Areas Levees meeting the design, closure, and inspection requirements listed above will be credited with providing protection from the one percent chance flood on FHBMs and FIRMs. However, the protected area will be identified with a note on the maps stating "This area protected from the 100-year flood by levee, dike or other structure subject to failure or overtopping during larger floods". All such areas will be shown as Zone B on the FIRM and as an area subject to the 500-year flood on the FBFM, to highlight the residual risk of flooding. Floodways will be delineated at the inside toe of mainline and tributary levees which are credited on a map. This will assure that no development will occur on the outside of the levee, which may jeopardize the levee's integrity, or effectiveness. As part of all future study, restudy or map revision effort, where credit will be given to levees providing IOO-year protection, the adequacy of interior drainage systems will be evaluated. Areas subject to flooding from inadequate interior drainage behind levees will be mapped using standard procedures. Often, shallow flooding zones, or even numbered A-Zones may be applicable in these instances. For the area contained within a levee (i.e. the protected area) providing less than IOO-year protection, the base flood elevation to be shown is that computed as if the levee did not exist. For the area outside of such a levee, the elevations to be shown are those obtained from the profile which would exist at the time levee overtopping begins, or from the profile cOmputed as if the levee did not exist, whichever is higher. This procedure recognizes the increase in flood elevation in the unprotected area which is caused by the levee itself. This procedure may result in flood elevations being shown as several feet higher on one side of the levee than the other. Both profiles should be shown in the study report and labeled as "before levee overtopping" and "after levee overtopping" respectively. Separate Floodway Data Tables should be prepared for each side of the levee and adequately labeled. The Flood Insurance Rate Map should show a gutter line, running along the levee centerline, separating the areas of different base flood elevations and zones. Flood Hazard Factors and Zones should be computed independently for each area using the standard procedure.