value of 0.025 for Manning's n, these curves represent deposition lengths 

 of between 6,400- and 38,400 feet. Note that the actual values of V^^ox ^^'^ 

 A critical ^^^^ above the curve n^L = 6. Thus for n = 0.025, the predicted 

 deposition length is less than 19,200 feet; the actual length is about 35,000 

 feet. Thus, the theoretical stability does not match actual conditions, 

 perhaps because of the jetty's effect on longshore sediment transport into the 

 inlet. 



d. Summary. In its natural state, Galveston entrance was a typical 

 downdrift offset inlet, similar to most inlets on the upper Texas coast. 

 Jetty construction caused extensive changes in the ebb tidal delta, with a 

 tripartite pattern of downdrift deposition offshore and in the fillet, and 

 erosion between these zones, and updrift deposition. This entrance appears to 

 effectively block any net westward transport to the beaches on Galveston 

 Island; longshore sediment transport is directed toward the inlet from both 

 the north and south sides. However, extensive sand deposits in the south 

 fillet and along the inside of the south jetty could be dredged and pumped or 

 hauled to nourish Galveston beaches. 



After a period of relative stability, the minimum cross-sectional area of 

 the entrance increased about 30 percent between 1933 and 1974 which, with an 

 essentially constant width. Increased the hydraulic radius by about the same 

 amount. Most of this change presumably resulted from dredging, although 

 construction of the Texas city dike (see Fig. 44) may have changed the ebb 

 flow direction sufficiently to increase the throat area. Limited data 

 indicate that, contrary to expectations, the tidal prism did not increase 

 proportionately. 



4. Rollover Pass . 



a. Historical Review. Rollover Pass (Fig. 56) , an artificial pass con- 

 necting Rollover Bay to the Gulf of Mexico about 22 miles northeast of 

 Galveston, was constructed by the Texas Parks and Wildlife Department to 

 enhance fish migration into East Bay and improve bay water quality and salin- 

 ity. A number of reports have been published on the characteristics and behav- 

 ior of Rollover Pass, the three most comprehensive being those by U.S. Army 

 Engineer District, Galveston (1958), Prather and Sorensen (1972), and 

 Lockwood, Andrews, and Newnam, Inc. (1974). The following brief historical 

 review is quoted from the latter report: 



"Engineering and ecological studies prior to 1954 established the 

 feasibility and desirability of a tidal inlet at this location. The 

 pass was constructed between October 1954 and February 1955. It had 

 an 80-foot bottom width and an 8-foot depth. Sloping earthen sides 

 were constructed except for the southwest side which was protected by 

 a steel sheet pile bulkhead. 



"Unusually high tides during 1955 resulted in extensive erosion of the 

 pass. The Gulf entrance widened to about 500 feet and the depth of 

 water under Highway 87 bridge increased to 30 feet. In November 1955, 

 in an effort to stop erosion, a steel sheet pile wall (sill) was con- 

 structed across the pass 40 feet south of the Highway bridge. Alter- 

 nate sheet piles of this sill were driven 2 feet below mean sea level 

 (MSL) to permit some water flow through the pass. A short steel sheet 



66 



