range of head differentials between the gulf and the bay were defined. 

 This information then formed the basis for definition of losses for the 

 Galveston Harbor Entrance as input to the mathematical model. Only that 

 part of the overall study concerned with the Galveston Bay inlet is dis- 

 cussed here. 



(7) The Model . An existing, comprehensive, fixed-bed model of 

 the Houston Ship Channel was used for the tests (Fig. 7-7). The model 

 limits were altered to confine the surface area of the model and to re- 

 duce the stabilization time required for the individual tests. An arti- 

 ficial outflow channel equipped with an adjustable tailgate was also 

 installed to facilitate the regulation of the water levels in the bay 

 and to channel the water into a collection sump. The model limits and 

 outflow channel, together with the locations of the water surface gages, 

 are shown in Figure 7-8. 



The model, including the harbor entrance, was molded to conform with 

 soundings in the prototype during July to October 1962. The model was 

 adjusted hydraulically soon after construction so that velocities and 

 current patterns observed in the prototype for normal tidal ranges were 

 accurately reproduced by the model (comparisons are shown in Fig. 7-9). 

 This adjustment was also assumed to be reliable for surge conditions 

 where water levels considerably exceed the high water level associated 

 with normal tides, because the physical characteristics of all existing 

 features were installed to scale and the correct overflow characteristics 

 of the jetties were determined by independent tests in an undistorted- 

 scale model. 



The jetties protecting the entrance are not overtopped by tidal 

 waters during normal tides, but during periods of hurricane surge flow 

 will occur over the jetties and into the entrance. Therefore, it was 

 necessary to install jetties in the model with the correct overflow 

 characteristics; this was accomplished by construction of a 300-foot- 

 long section of jetty to an londistorted scale of 1:100. Tests were then 

 conducted in the undistorted-scale model to define the hydraulic charac- 

 teristics of the jetty. Finally, with the desired properties known, a 

 jetty shape which would duplicate these properties in the Houston Ship 

 Channel model (distorted scale) was developed and molded into the model. 



(8) Test Procedures . The test procedures consisted of stabi- 

 lizing the flow in the model so that the water surface elevations of the 

 Gulf of Mexico, West Bay, and Galveston Bay were at predetermined eleva- 

 tions of interest. The stabilized elevations of the water surface of 

 West Bay and Galveston Bay were established essentially identical for 

 any specific tests. The inflow to the Gulf of Mexico, the elevation of 

 the tailgate located at the end of the outflow channel, and the cross- 

 sectional area at the outflow channel in West Bay were adjusted until 

 the desired elevations of the water surface were obtained. The dis- 

 charge through the inlet was defined and all gages (see Fig. 7-8) were 

 monitored for each test. 



490 



