In an effort to assess the possible changes to physical oceanographic processes that might result from alteration of bathymetry as a result of dredging or sand mining, we evaluated the differences in the output of various numerical models run with the natural and hypothetical post-dredging bottom conditions. Fenwick and Isle of Wight Shoals offshore of the Delaware-Maryland border of the mid-Atlantic continental shelf served as the test site. We considered two dredging scenarios, a one-time removal of 2 × 106 m3 of sand from each of two shoals and a cumulative removal of 24.4 × 106 m3, but only the larger appeared significant.
The study of wave transformation processes relied upon a series of runs of the REF/DIF-1 model using sixty wave conditions selected from analysis of the records from a nearby, offshore wave gauge. The model was tuned and calibrated by comparing measured near-shore wave conditions with data calculated using the same measured offshore waves that generated the real near-shore conditions. The modeled, post-dredging data indicated an increase in wave height of up to a factor of two in the area between the dredged shoals and the shore and, in some locations, a lesser increase in breaking wave height and a decrease in breaking wave height modulation. The model results also may help explain the existing pattern of erosion and relative stability.
Application of the well-known SLOSH model (Sea, Lake, and Overland Surges from Hurricanes) for storm surge and POM (Princeton Ocean Model) for tidal currents indicates that the likely dredging related changes in those processes are negligible.