Evaluating Shoreline Response to Offshore Sand Mining for Beach Nourishment

An analytical approach that incorporates analysis of nearshore wave transformation and wave-induced longshore sediment transport was developed to quantify the significance of potential physical environmental impacts associated with offshore sand mining. Calculation of longshore sediment transport potential for a series of wave cases provided a method for determining the extent and magnitude of alterations to nearshore processes, but the magnitude of change alone did not provide enough information to determine the significance of changes for a particular coastline. This paper documents a method for evaluating the significance of borrow site impacts that incorporates temporal and spatial variations in the incident wave field. Example applications of this method are presented for borrow sites offshore Oregon Inlet, North Carolina; Martin County, Florida; and Corsons Inlet, New Jersey. As a management tool, this methodology holds several advantages over methods previously employed to assess the significance of borrow site impacts, including: 1) a model-independent component (observed shoreline change) is used to verify model results; 2) impacts associated with borrow site excavation can be directly related to their potential influence on observed coastal processes; 3) site-specific temporal variability in wave climate and sediment transport potential is calculated as part of the methodology; and 4) the procedure accounts for spatial and temporal variability in wave climate, as well as provides a means of quantifying significance of impacts relative to site-specific conditions.