the entrance has remained relatively constant since 1850 at about 9,500 feet, 

 but the cross-sectional area and hydraulic radius have increased from 13,000 

 to 19,000 feet and 14 to 21 feet, respectively. 



As at San Luis Pass, the large deposition volumes at Galveston could be 

 used for beach nourishment, particularly the southwest fillet and the adjacent 

 spit extending eastward into the channel. Located only a few miles from the 

 Galveston Beach groin field, the sand has little functional importance in its 

 present state, and it is probably the most economical borrow site, both in 

 terms of grain-size characteristics and transportation costs. 



b. Tides and Hydraulics. Tidal ranges in Galveston Bay increased about 

 12 percent between 1936 and 1974, and are presently about 0.56 that of the 

 Galveston Pleasure Pier. This increase is considerably less than might be 

 expected, based on the observed 25-percent increase in minimum cross-sectional 

 area. The average diurnal tidal prism is about 11 x 10^ cubic feet, but ebb 

 discharges during northers were more than three times as great and must con- 

 tribute significantly to natural maintenance of the channel. 



5. Rollover Pass. 



The history of this small manmade inlet offers an object lesson in proper 

 inlet design considerations. First, numerical or physical model studies of 

 proposed plans should be performed to determine the effects of any inlet on 

 the bay system, and to predict the flow characteristics through the inlet. 

 Creation of Rollover Pass increased the East Bay tidal ranges by about 10 

 percent and currents were extremely rapid, due to initially low frictional 

 resistance. Subsequent installation of a weir and growth of a flood tidal 

 delta increased friction to a Manning's n value of 0.032. Second, inlet 

 stability should be assessed: Will the planned inlet be unstable, i.e., in 

 scour or deposition modes, or will it be in harmony with the local tide and 

 wave regimes? Third, inlets typically act as sediment sinks, removing 

 material from the longshore transport regime through development of fillets 

 and ebb and flood tidal deltas. Removal of this material and the resulting 

 deficit in available littoral material typically produces downdrift beach 

 erosion. At Rollover Pass, the excess volume removed from the beaches was 

 almost exactly equal to the volume deposited in the inlet. 



6. Sabine Pass . 



a. Bathymetric Changes . Although the material comprising the present 

 nearshore and channel bottoms is much finer than that of other Texas coast 

 inlets, Sabine Pass postconstruction bathymetric changes closely parallel 

 those at Galveston — updrift, deposition in a fillet with offshore erosion; 

 downdrift, a tripartite pattern of deposition-erosion-deposition (Fig. 73). 

 Lack, of sufficient survey data precludes calculation of the total amounts of 

 material which accumulated near the pass, but within the data limits there was 

 a net accretion of 900,000 cubic yards on the updrift side and 2 million cubic 

 yards on the downdrift side between 1885 and 1974. 



b. Tides and Hydraulics. Available tide data indicate that the annual 

 mean bay tidal range has remained constant at about 50 percent of the pass 

 range since 1936, although the pattern of seasonal variability in range dif- 

 fers greatly. The mean pass range between 1960 and 1975 was 1.85 feet. Ebb 

 flows predominate between the jetties (1.24:1, ebb:flood) due to freshwater 



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