area for Plan 1. The extension of the navigation channel at the seaward end 

 produced almost no effect upon the current patterns. 



Sediment Transport 



Testing procedure 



121. The testing procedure used was similar to that for base conditions 

 except the computations were performed with Grid 2, and the bathymetry at the 

 start of computations corresponded to Plan 1 conditions. The sediment trans- 

 port model used the results of the tide model for Plan 1 and the results of 

 the wave and wave-induced current models for base conditions. As for the base 

 test, computations were performed for 200 days of prototype time, and the 

 results were used to estimate yearly erosion/deposition rates along the 

 channel. 



Results 



122. The channel was divided into 11 zones for Plan 1 (Figure 23). The 

 exact offshore limit of zone lA was yet to be determined from field surveys. 

 Figure 27 shows the erosion/deposition rates by zone for Plan 1. A comparison 

 of base and Plan 1 results is plotted in Figure 28. The model predicts an 

 increase in both deposition rates and erosion rates between sta -97+76 and 

 sta 325+00 from base to Plan 1. Zone lA is not shown in the figure. This 

 zone indicates on the average a slight erosional tendency with rates of the 

 order of 0.1 ft/ year or less. The model predicts deposition in zones 8 and 9 

 (sta 323+02 to sta 374+94) for both base and Plan 1. For Plan 1, the deposi- 

 tion rates are of the order of 1.0 to 1.4 ft/year. Model B predicts large 

 erosion rates in zone 10 (sta 374+94 to sta 399+74). Since there is no quan- 

 titative field information on sedimentation rates in zones 8-10, it is diffi- 

 cult to comment on Model B predictions for this reach. It is suspected that 

 since the bathjnnetric information used for this channel reach and adjacent 

 areas was not up-to-date, it might have caused deviation of Model B results 

 from field experience. Another contributory factor might be the grain sizes 

 found in this reach, which are much larger than elsewhere in the study area. 

 The model assumes the same grain size distribution throughout the study area. 

 The local deviation of grain sizes might have resulted in the prediction of 

 larger erosion and deposition rates locally. There is reason to believe the 

 effect of these factors is restricted to Model B predictions for zones 8-10 



71 



