Analysis of FEMA Guidelines for Coastal Dunes Using a Numerical Model
Date of Award
Master of Science (MS)
Civil & Environmental Engineering
David R. Basco
Call Number for Print
Special Collections LD4331.E542 P39 2010
FEMA's current guideline for coastal dune erosion is called the 540 Rule. The intent of the 540 Rule is to act as a boolean guideline for dune protection. If a dune is validated as being substantial against the 1 % Annual Chance Storm Water Elevation Level by the 540 Rule, then the area behind the dune is considered to be susceptible to less energetic flooding. This is known as an AE Flood Zone. An immediate effect of being rezoned is a significant drop in the insurance costs behind the dune. However, if the dune is not validated by the 540 Rule, then it is assumed that the dune is not substantial enough to protect the area behind the dune, and this area therefore is labeled as a VE Zone. Under a VE Zone, construct requirements are considerably stricter, and existing structures will have a significantly higher flood insurance rate than if they were zoned as AE.
The one dimensional cross-shore beach change model known as SBEACH was selected to test the 540 Rule. Five severe storms were modified to be the 1 % annual chance SWEL for two beach profiles provided by FEMA. The PFD of one beach profile is about 20% greater than 540 ft3 /ft, and the other profile is about 20% less than 540 ft3 /ft. The FEMA beach profiles were not detailed enough offshore and were modified using data from the nearby U.S. Army Corps of Engineers Field Research Facility.
The results of the simulation concluded that the five storms applied to the two beach profiles all performed within the definition of the 540 Rule. Of particular importance, the dune which the 540 Rule defines as an effective barrier against the 1 % Annual Chance Storm Water Elevation Level never eroded beyond the dune heel. Therefore, in this study, the 540 Rule is found to be an appropriate means of primary frontal dune evaluation.
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Payne, Brenton E..
"Analysis of FEMA Guidelines for Coastal Dunes Using a Numerical Model"
(2010). Master of Science (MS), Thesis, Civil & Environmental Engineering, Old Dominion University, DOI: 10.25777/74fy-2482