Historical Findings on Ebb Shoal Mining
Keywords:Beach erosion, beach nourishment, tidal delta, longshore drift, coastal management, shore protection
Mining of ebb shoals has become more prevalent in recent years due to limited sources of beach quality sand available for beach nourishment projects. This paper examines eight ebb shoal mining projects completed since 1981 in an attempt to examine this relatively new practice of removing material from an inlet ebb shoal. A brief description of each inlet's history, morphology, and processes is given in an Appendix for background information and available information on the ebb shoal mining events at each inlet is presented in this paper. The eight projects presented range in size from 170,000 m3 removed from the ebb shoal at Boca Raton Inlet (Florida) to 6,235,000 m3 removed from the ebb shoal at Great Egg Harbor Inlet (New Jersey). The recent completion of many of these projects and lack of systematic monitoring has resulted in limited monitoring data to assess shoal mining impacts on the inlet system. With this in mind, impacts of ebb shoal mining inferred from the data and the level of monitoring at each project site are discussed. From this study, it has been determined that most ebb shoals are mined on the outer "passive" portion of the shoal feature. Ebb shoal sand was found to be compatible with the native beach material, indicating that the ebb shoal acts as a "sand bridge" between the updrift and downdrift beaches. The rate of recovery of the mined area appears to be a function of the degree to which the system equilibrium is perturbed, sand availability (longshore transport rate), storm frequency, and the depth of the mined area. Estimates of borrow area recovery were often overpredicted, probably due to poor longshore transport estimates. Further analysis is needed to determine ebb shoal mining impacts to navigation, inlet adjacent shoreline, ebb shoal equilibrium, and reusability of borrow area infill material. This paper is an attempt to evaluate the state-of-the-art in the practice of removing material from inlet ebb shoals and monitoring of these projects. A suggested monitoring plan for future ebb shoal mining projects is also presented.