Evaluating Transport Formulations for Application to Nearshore Berms

Abstract

Dredged sediment is commonly placed as a submerged nearshore berm to nourish the beach or to dissipate high-energy waves, but the lifespan of such features is not easily predicted by existing methods. This paper presents a simple technique for generating order-of-magnitude estimates of the sediment transport rate of nearshore berms using offshore hindcast wave characteristics transformed to the nearshore. Total longshore transport for the entire nearshore region is calculated using eight published longshore transport equations (e.g., CERC equation and Kamphuis equation), which were evaluated for their relative performance. Because nearshore placements occupy only a portion of the crossshore profile, the total longshore transport rate is scaled by an empirically-based fraction between 0 and 1, which is determined by the nearshore berm's position in nondimensional space. The cross-shore transport rate is calculated independently using the near-bed orbital velocity from stream-function wave theory. The longshore and cross-shore transport rates are then superimposed to generate a total transport rate for the nearshore berm's constructed footprint. The total transport rates were calculated at 11 historical nearshore berms and evaluated based on accuracy, inclusion of relevant coastal processes, and sensitivity to input parameters. The recommended total transport rate technique resulted in an average percent error magnitude of 72% and a maximum percent error magnitude of 167% at the historical placement locations. This technique is recommended for generating rapid, order-of-magnitude estimates of nearshore berm deflation rates for project design, particularly in scenarios when application of a full numerical model is prohibitive.

Beach Response to a Shoreface Nourishment (Aveiro, Portugal)

“…Although the results presented above also allow to better understand the beach response to a shoreface nourishment at Aveiro, more coastal monitoring is definitely desirable to draw more firm conclusions. The use of simple techniques to assess shoreface nourishment expected evolution can be of interest for preliminary designs [38]. Additionally, the use of video cameras can be included to complement topographic and bathymetric measurements [39].…”

Current state of practice of nearshore nourishment by the United States Army Corps of Engineers

“…Additionally, placed sediment can dissipate wave energy, thereby reducing wave energy on the beach profile. Nearshore nourishment provides a favorable alternative to both direct beach placement and offshore disposal, as it can be less expensive due to lower mobilization costs and allows for less-than-beach-quality sediment to still be used beneficially (Brutsché et al 2019;Bain et al 2021;McFall et al 2021b).…”