of 60°) was used as input for all four cases. Case 4.2a used an equilibrium 

 shape factor A of 0.0899 and one groin. Case 4.2b was similar to 4.2a with 

 the only modification being, that the A value was changed to 0.1486. In this 

 way, a direct comparison was made based only on the shape of the equilibrium 

 profile. Cases 4.2c and 4. 2d used A-values of 0.0899 and 0.1486, 

 respectively, but this time three shore-perpendicular, evenly spaced 

 structures were simulated. 



a. Comparison of Cases 4.2a and 4.2b . The most obvious difference between 

 Figures 7 and 8 is the volume of sand impounded updrift and eroded downdrift. 

 This is due to blockage of more of the active transport zone in the second 



case (i.e., a shorter groin is required for an equivalent performance on a 

 steeper beach). The next obvious difference is the size of the perturbation 

 which exists in the offshore contours. Clearly, case 4.2b is more pertarbed 

 and this is expected because larger offshore transports occur due to the 

 steepening on the updrift side. Conversely, this means less sediment is 

 initially bypassed (and along with the downdrift requirement for larger 

 volumes of sand) causes larger erosional features in case 4.2b. Another 

 interesting feature is the downdrift fillet which occurs in the third, 

 fourth, and fifth contours. The fillet is due to the shape of the sixth 

 contour which occurs because of the inability of the wave to transport more 

 sediment (due to the reduction in wave height and angle in the diffraction 

 shadow zone). The remaining difference is also due to the volume of sediment 

 being impounded; i.e., the distance and extent of change the presence of the 

 groin causes upcoast and downcoast. 



b. Comparison of Cases 4.2c and 4. 2d . The variations between cases 4.2c and 

 4. 2d are \/ery similar to the differences between cases 4.2a and 4.2b as would 



be expected with a groin field (here, three groins) as compared with a single 

 groin (see Figs. 9 and 10). There is, however, one additional feature which 

 can be attributed to the additional groins. Note that in the direction of 

 littoral drift, the size of the fillet is decreasing. This is due to the 

 updrift beach having an uninterrupted supply of sediment while the downdrift 

 groin compartments are supplied sand at a rate determined by the bypassing. 

 Part of this feature may also be due to the system not having attained 

 complete equilibrium. 



The effects of the fixed boundary conditions are evident on all cases 

 run. In these example cases, the boundaries are clearly too close to the 

 structure to provide a proper representation of the fillet contours. 



3. Simulations of Sediment Transport of Dredge Disposal in the Vicinity of 

 Oregon Inlet . 



Hypothetical dredge disposal movement in the nearshore but beyond what 

 is normally the surf zone at Oregon Inlet's adjacent beach to the south was 

 modeled. In order to do these simulations, the program was altered such that 

 for every at!l iteration (time periods), the contours were shifted seaward 

 to simulate the addition of dredged sediment disposal. The program presented 

 in Appendix B does require slight modification to simulate this situation. 



In general, the fifth and sixth contours were shifted seaward on a 

 monthly basis to simulate the disposal of 121,000 cubic yards of sediment. 



30 



