Dynamic shoreline response to a shallow concentrated nearshore berm nourishment

Abstract

Worldwide, coastal regions are pressured due to sea-level rise and the increased likelihood of extreme events. Traditionally, hard engineering techniques were used for shoreline protection. However, due to the negative side effects at adjacent beaches, a switch was made to more sustainable soft solutions, such as nearshore berm nourishments. Although several manuals are available describing the preliminary design of nearshore berm nourishments, most of them are based on expert judgment and not on quantitative predictions, which potentially leads to design flaws and, therefore, to unnecessary costs. To overcome this problem, this research aims to increase the understanding of the development of nearshore berm nourishments in relation with the corresponding shoreline evolution by analyzing a shallow concentrated placement at New Smyrna Beach. It is found that the theoretical Feeder and Leeside effects played an important role in shoreline dynamics. The Feeding effect is characterized by shoreward propagating accretionary waves (SPAWs) while the Leeside effect is depicted by shoreline erosion patters downdrift of the nourishment induced shadow zone. Contrary
to most nearshore berm nourishments, the placement at New Smyrna Beach resulted in a significant increase of 45.000 m2 of the sub-aerial beach. Although not validated in this study, it is hypothesized to be a result of
the high cross-shore density of the nourishment, ¼ 875 m3/m, and shallow placement location of 4-5 meters.