BEACH NOURISHMENT IN PRESENCE OF SEAWALL

Beach nourishment, placed along a seawalled shoreline, can exhibit a markedly different behavior than projects on shorelines with adequate compatible sands to transport. The most striking effects of engineering significance are: (1) The migration of the centroid of the nourishment planform anomaly when acted on by oblique waves; and (2) a potentially different (currently unknown) rate of spreading of the planform anomaly. Under the most idealized considerations of uniform transport along the nourished shoreline. the speed of centroid migration is shown to increase as the planform anomaly spreads out under the mobilizing action of the waves, and the rate at which the planform spreading (dispersion) occurs is not affected by the seawall. Also, for normally incident waves, the seawall does not affect the planform evolution. Analytical, numerical, and experimental approaches are employed to demonstrate the aforementioned effects. It is shown that the transport at the ends of the project, where all the nourishment sand is submerged, can affect results substantially. These effects of the presence of a seawall on beach-nourishment project performance appear to have not been reported previously.