quantity moving onshore could be caused by waves that first tend to move more 

 sediment longshore; then, the waves that transport more sediment onshore have 

 a less out-of-equil ibrium profile to cause movement upon. The variation in 

 percentage remaining is due to the variation of the time series of the wave 

 climate, with the last month in the simulation being especially important. 



(5) Case 3 . Instead of extending the 7- and 11-foot contours monthly to 

 simulate the disposal of dredged sediments, the 11- and 14-foot contours were 

 extended (194.4 feet each at the center of the disposal area). This case was 

 modeled because the larger available dredge could not dump in more shallow 

 water. The reduction and increase in the percent of onshore volume and the 

 percent volume remaining (8.9 percent and 78.0 percent, respectively) 

 demonstrate the sensitivity of the depths investigated. Qualitatively, these 

 depths are the depths to which offshore bars occur along the Atlantic U.S. 

 coast. 



(6) Case 4 . Further investigation of the disposal process demonstrated 

 the need for an 11,000-foot shore-parallel disposal length with the sediment 

 placed at the 11-foot contour building to about 7 feet. It was decided to 

 model this physical situation also. The total shoreline length was changed 

 to 20,000 feet, and the space step to 400 feet; the length of the disposal 

 area in the longshore direction was increased to 10,800 feet. The resolution 

 in the vicinity of the depths of the dump was improved by adding the 

 additional contours and the profile is shown in Figure 16. As in the other 

 seven cases, 1,452,000 cubic yards was added annually to the system; however, 

 the addition was accomplished on a weekly basis (27,923 cubic yards per 

 week). Sediment was still added by extending the contours seaward, but 

 rather than placing one-fourth of the sediment at each of the four contours, 

 the volumes were determined based on the trapezoidal cross section shown in 

 Figure 17. This cross section more closely resembles the disposal mound 

 formed by hopper dredging. The incremental values Figure 18 show, in 

 planform, the extension of the contours to simulate the weekly sediment 

 addition at the 8-foot contour. 



A schematic illustration of the sediment transported from the nourished 

 region is presented in Appendix C. Nineteen percent of the sediment added 

 moved directly onshore out of the control volume. 



b. Conclusions for the Movement of Disposed Sediment in the Vicinity of 

 Oregon Inlet . The computer simulations, tempered with engineering judgment, 

 demonstrate tnat between 15 and 35 percent of the material added to the 7- 

 and 11-foot contours, or to the 7- 8- 9-, and 10-foot contours would be 

 transported into the nearshore transport system during the first year. If 

 the disposal process was continued, the system would approach steady state in 

 terms of the volume of deposited material residing offshore. 



For the case of sediment addition at the 11- and 14-foot contours, the 

 computer simulations, tempered with engineering judgment, show that between 5 

 and 25 percent of the material added would be transported into the nearshore 

 transport system during the first year. 



43 



