|The Offshore Sand Resources Study||contact: Bob Conkwright (email@example.com)|
Linear Sand Ridges
(page 3 of 1, 2, 3, 4, 5)
Our second objective in the Offshore Sand Resources was to determine which shoals were most likely to contain sand suitable for beach nourishment. Of particular interest to this study is a model introduced by McBride and Moslow (1991), which describes the formation of linear sand ridges. This model details the evolution of ridges formed when inlet shoals become submerged during sea level rise, and are subsequently reshaped by ocean waves and currents. The process can be summarized in six steps:
Linear ridges can evolve from several processes. The McBride/Moslow model offers a mechanism to explain why many linear ridges share common physical features. Ebb-tidal deltas that form at the mouths of inlets trap sand moving past and through the inlets. Therefore, sand ridges that have developed from ebb-tidal deltas have an excellent sand resource potential.
We applied the McBride/Moslow model to geologic data from the inner continental shelf to determine which sand ridges, or shoals, might have been ebb-tidally derived. These shoals have the best potential as sand resources. This method was employed primarily to narrow the number of shoals targeted for further investigation. Field operations to collect data on the shoals are expensive. Therefore, it was necessary to maximize the probability of locating sand resources before sampling projects were initiated. We also limited our search to within 24 km of the shoreline, and to water depths of less than 15 meters. These limitations were based on the economics and mechanics of dredging the shoals and emplacement of sand on the beaches. Eight shoals out of nineteen were targeted for sampling by applying the McBride/Moslow model to our geophysical data.