Beaches are dynamic in nature as they are likely to continue to erode over time due to winds and waves, which reduces the effects of nourishment projects on flood hazards landward of the beach. Therefore, without regular maintenance, a raised or widened beach is only temporary. When coastal flood hazard mapping studies are performed, FEMA takes beach nourishment projects into consideration only when the project is significant (i.e., has the dimensions necessary to affect 1-%-annual-chance flood hazards) and will be maintained for many years. Dunes are also dynamic as they are subject to erosion, overwash, and could be washed away during major storms. Many nourishment projects incorporate a dune - either new or rebuilt - at the landward edge of the beach, although in some cases dunes are enlarged or constructed separately.
Not all nourishment projects will affect the 1-%-annual-chance flood hazard - either because the project is small, the dune lacks vegetation, the community cannot demonstrate a commitment to future maintenance, or other reasons. FEMA's experience evaluating these projects shows:
- Many nourishment projects have beach elevations that are too low to alter upland wave hazards;
- One-time projects without assurance of future maintenance will only have a temporary effect on flood hazards; and
- Newly constructed dunes lack long-standing vegetation, making them more susceptible to erosion.