extension stopped wherever the natural ocean depth became equal to or greater 

 than 49 ft mlw. (This location of the oceanward entrance of the navigation 

 channel would be determined In the field from the latest bathjrmetric surveys 

 for the final channel design.) In the navigation channel itself, the planned 

 channel depths were used. The bathymetry used outside the channel was the 

 same as that for base condition. 



Tides 



118. To properly model the sand-tightened section of the south jetty in 

 the numerical model, the crests of the barriers simulating this jetty section 

 were raised to the prototype jetty elevation of +3 ft msl; and the Manning's 



n values governing flows over the barriers were changed appropriately. 



119. Plates 16-19 compare the computed base and Plan 1 velocities 

 (magnitudes and phases) at seven sites in the inlet (refer to Table 1 and 

 Plate 7 for locations of these sites) . All of the changes in tidal currents 

 are due to sand- tightening of the south jetty. The peak velocity at tide 

 Gage 1 (Plate 16) has increased by approximately 10 percent between base and 

 Plan 1 due to sealing of a section of the south jetty. The gages at the 

 throat of the inlet (Endeco velocity Gage 2, range survey Gages 1-A, 1-B, and 

 1-C, and Fort Clinch) (Plates 16-19) show negligible change in velocity. The 

 velocity at the ocean end of jetties (Plate 18) increases by about 10 percent 

 in both ebb and flood for Plan 1 and shows a slight phase shift. 



120. Plates 20-21 show the tidal current patterns near the inlet for 

 maximum ebb and flood for Plan 1. For clarity, the plotting of velocities 

 below 0.1 fps is suppressed in these figures. These two plates can be com- 

 pared to the base condition patterns of Plates 14-15, but few differences are 

 apparent in a visual examination. For convenience the vector differences 

 between Plan 1 and base condition velocities are shown in Plates 22-23 for the 

 same region near the inlet, for maximum ebb and flood, respectively. Note the 

 change in velocity scale. The plotting of velocity differences below 0.05 fps 

 is suppressed in these figures. Both figures indicate that sealing the south 

 jetty exerts local changes on tidal currents. The large difference vectors at 

 the landward end of the south jetty represent a decrease in velocities between 

 base and Plan 1 since flows in this area are stopped by sealing the jetty. No 

 other significant changes in the current patterns were noted within the study 



70 



