Performance of Structural Alternatives for Sediment Control at North Jetty, Grays Harbor, WA

The US Army Corps of Engineers (USACE) has undertaken a thorough study of coastal processes in and around the entrance to Grays Harbor, WA, in order to optimize the performance of the North Jetty. As part of this study, detailed numerical modeling of 2D nearshore circulation and sediment transport was conducted to evaluate the impacts of a number of structural alternatives on waves, water levels, nearshore circulation and the resulting sediment transport relative to existing conditions (MacDonald et al., 2003). This work was done to examine the sensitivity of these impacts to variations in nearshore bathymetry. This paper summarizes the approach and findings of this fine-scale nearshore modeling work. Five structural alternatives were investigated along with two sets of bathymetric conditions in order to account for the year-to-year variability in nearshore morphology. Several numerical models were used to study the waves, circulation patterns, sediment transport potential and sediment bypassing. Ninety-six simulations were performed for each structure-bathymetry combination to represent the local tide and wave climate. A novel approach of this work was the analysis of the results in terms of an annualized climate. The results of this fine-scale nearshore modeling work showed that all alternatives were successful, to varying degrees, in promoting sediment retention on the adjacent beach and in reducing sediment bypassing into the inlet.