in Figure 3-74. Various barrier beach sections were also subjected to 

 undistorted-scale flume tests to determine the appropriate discharge 

 characteristics for use in the mathematical model. Similarly, the 

 Houston Ship Channel model was subjected to detailed tests to determine 

 the discharge characteristics of the entrance and barrier beaches for 

 use in the mathematical model. 



(9) Summary of Test Results . The testing program in the surge 

 model consisted of tests with two major barrier plans, designated Alpha 

 and Gamma. The locations of the two plans and two representative tide 

 gages are shown in Figure 3-75. The Alpha plan barrier was located 

 generally just behind the gulf beaches and would protect all low-lying 

 areas adjacent to Galveston Bay complex and tributaries. The Gamma plan 

 barrier was located about 9 miles upstream from the entrance and afforded 

 no protection to the barrier beaches or other low- lying areas downstream 

 of the barrier, including Galveston. These two barriers were tested with 

 gated and ungated navigation openings for three hurricane surge condi- 

 tions. Since the tidal flow gates would be closed by the time a hurri- 

 cane surge came inland, only navigation openings in the barriers were 

 involved in surge tests. 



Figure 3-76 shows a comparison of three hurricane surge histories 

 at a point near the Galveston Bay entremce. One of the hurricane surges 

 investigated represented a hypothetical (design) surge resulting from a 

 large radius, slow translation (LRST) hurricane that would generate a 

 maximum surge of about 10.5 feet at the Galveston Bay entrance about 100 

 hours after the wind field arrived at the Continental Shelf. This type 

 of hurricane, even though the peak elevation was lower than the large 

 radius, high translation (LRHT) hurricane, resulted in higher surge ele- 

 vations landward of the barriers. This is attributed to the slow approach 

 speed of the storm, which allows a gradual water level buildup behind the 

 barriers as a result of the long period of flow through the navigation 

 opening. Typical results of tests conducted with this slow storm and the 

 Gamma and Alpha barriers are shown in Figures 3-77 and 3-78, respectively. 



The results of studies conducted on the Galveston Bay surge model 

 indicated that both the Alpha and Gamma hurricane barrier schemes would 

 effectively protect v^stream areas from damage caused by hurricane surges 

 originating in the Gulf of Mexico. The degree of protection afforded 

 would be significantly greater with a gated navigation opening than with 

 an ungated opening. The ungated Alpha barrier would provide better pro- 

 tection than the ungated Gamma barrier. 



The Houston Ship Channel model (Fig. 3-71) was used to investigate 

 the effects of the two barrier plans (Alpha and Gamma) on tides, currents, 

 salinities, and dye dispersion within the bay system. Tests conducted 

 with the proposed Alpha design plan (Fig. 3-79) indicated no significant 

 effects on tidal elevations, ranges, or times. Maximum current veloci- 

 ties in the navigation opening would be about 4.7 feet per second. Tests 

 further showed that a 20-percent reduction of total area of tidal pas- 

 sages proposed in the original design caused this maximum velocity to be 

 increased to about 5.1 feet per second (which is considered about the 



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