hoppers and the loaded and unloaded drafts of each vessel. Disposal depths 

 were -11 ft and -17 ft MLW for the CURRITUCK and ATCHAFALAYA/MERMENTAU 

 classes, respectively (based upon a 3-ft clearance of each vessel to allow for 

 vessel vertical motions that would occur as a result of steep shoaling waves 

 in the nearshore area) . The dredges would continue the dumping pattern until 

 the end of the disposal area was reached. Then the pattern would begin again. 

 If the material in the first disposal mound were sufficiently dispersed to al- 

 low the dredges to dump material once again, the second disposal mound would 

 be located where the first mound was dumped. If not, a second row of material 

 would be dumped immediately behind the first. This placement of mounds would 

 continue indefinitely with attempts made to dump the material in the shal- 

 lowest depth of water available (depending upon the dispersal of earlier 

 mounds) . 



92. A key question about the feasibility of the DOI proposed nonstruc- 

 tural solution was whether the material placed in the nearshore area would be 

 dispersed shoreward by wave action at a rate sufficient to prevent dredging- 

 induced beach erosion. To address this question, only the profile response 

 (onshore-offshore transport) model described in this report was used since the 

 material to be deposited would be away from the area where tidal currents are 

 significant and in an area where bathymetric contours are approximately 

 straight and parallel. Changes in the rates of onshore-offshore sediment 

 transport resulting from the disposal of the dredged material were determined 

 from the differences between the sediment transport rates computed for a 

 control profile (i.e. a profile without the dredged material) and the sediment 

 transport rates computed with the dredged material in place on the profile. 

 The calculations were accomplished using wave and tide conditions for 1975 

 which were determined to represent typical conditions in the Oregon Inlet 

 area. 



93. The hindcast wave conditions for 1975 were provided by the WESWIS in 

 10 m of water and at 3-hr intervals throughout the year. The astronomical 

 tide for 1975 was generated using tidal constituents. SAW supplied an initial 

 profile that was representative of the region where the dredged material would 

 be dumped (Plate 1). 



9h . The profile was modified by making comparisons between the dumped- 

 material profiles and the control profile every time-step. The width of the 

 surf zone was determined by assuming that the breaking depth was the shoaled 



72 



