Beaches and coastal areas take the brunt of climate change effects. More powerful tropical storms and hurricanes, sea level rise, increased wave action, and coastal flooding are exacerbating coastal erosion of sand and rock. Nearshore nourishment programs have been the main line of defense to combat erosion. But could navigational channels and dredging help extend the lifespan of beach nourishment? Comparing beach nourishment lifespan predictions is the goal of a new paper in the Journal of Waterway, Port, Coastal, and Ocean Engineering.
Authors Douglas R. Krafft, Brian C. McFall, Jeffrey A. Melby and Bradley D. Johnson sought to modify an existing one-dimensional numerical model so it could predict the lifespan of subaerial beach nourishment, factoring in the impact of using sediment in the nearshore. Using Galveston Island, Texas, as a case study the researchers considered three different simulations: 1) without nearshore nourishment, 2) with nearshore nourishment but without any impact of net alongshore transport, and 3) with nearshore nourishment and including the associated gradient in alongshore transport. They developed simulations of representative storm impacts on the dunes and compared those with and without nourishment. Their findings outlined in their paper, “Lifecycle Analyses of Subaerial Beach Nourishments with Concurrent Nearshore Placement of Dredged Sediment and the Role of Alongshore Transport” will be of interest to USACE and other agencies responsible for managing coastal storm risks. Learn more at https://ascelibrary.org/doi/10.1061/JWPED5.WWENG-2152. The abstract is below.
Abstract
Beach nourishment has a high cost but offers large economic benefits. Therefore, extending the nourishment lifespan using dredged sediment from navigation channels could have a significant economic impact. This numerical modeling study develops and compares two approaches incorporating nearshore sediment placements into an existing one-dimensional numerical modeling procedure to predict the lifespans of subaerial beach nourishment strategies. Both approaches build directly on the stochastic lifecycle simulation methodology and results used in the Coastal Texas Protection and Restoration Feasibility Study. Simulations for western Galveston Island were modified to include annually recurring nearshore nourishment. Cross-shore beach transects were forced with 50 years of tropical cyclones and nontropical storms in a cross-shore morphological evolution model, and rebuilt when the dune eroded to half of its initial height. One group of simulations applied this previously developed model forcing to cross-shore profiles that were updated with recurring nearshore nourishments. A second group of simulations included a simplified representation of sediment deposition from the alongshore transport gradient created by the nearshore nourishments. In both sets of simulations, a large sediment feature was incrementally constructed at depths between 2.5 and 6 m. Over 30 life cycles, the number of times the beach was rebuilt was tracked for each 50-year simulation. Comparing the number of predicted beach renourishments indicates that this particular nearshore nourishment strategy did not substantially impact the subaerial beach morphology unless alongshore transport gradients were also included. Simulations that did include this alongshore transport gradient predicted 23% longer lifespans. This work was not able to incorporate validation against measured data, but future testing of this approach should be pursued before widespread or high-impact application. Modeling results indicate that alongshore processes are an important part of quantifying the positive impacts of nearshore nourishment.
See how these findings could enhance your erosion management in the ASCE Library: https://ascelibrary.org/doi/10.1061/JWPED5.WWENG-2152.
