(4) Test Period . May 1960 to February 1966. 



(5) Problems . At the time of the model study, the jetty channel 

 at the entrance to Galveston Bay had three major problems: (a) the ex- 

 tremely sharp turn, located at approximately the inner end of the jetty 

 channel which caused difficulty for larger ships, especially tankers, to 

 negotiate at or near the strength of the tidal currents; (b) the extremely 

 deep water immediately alongside the north jetty in the area where the 

 navigation channel was close to the structure (the concern was that, dur- 

 ing a severe storm, a section of the jetty might slough into the channel 

 and block navigation); and (c) shoaling in the inner and outer bar parts 

 of the navigation channel (for the depth of -38.0 feet of the inner bar 

 and -40.0 feet of the outer bar, the average annual shoaling rates were 

 452,000 cubic yards and 731,000 cubic yards respectively). A location 

 map of the problem area is shown in Figure 7-16. 



As part of the improvement desired, it was anticipated that the depth 

 throughout the entrance channel would be increased by 2 feet, and an in- 

 crease of shoaling in both the inner and outer bars could logically be 

 expected. 



(6) Purpose of Model Study . The Galveston Bay and Harbor En- 

 trance Channel model study was conducted to: 



(a) Develop plans for relocation and stabilization of 

 the jetty channel on an alinement and at a depth suitable for the 

 safe passage of supertankers; 



(b) determine means for protecting the north jetty from 

 the undermining action of tidal currents; 



(c) determine the shoaling characteristics of the re- 

 located and deepened inner bar parts of the jetty channel, and 

 develop plans for minimizing shoaling in the relocated channel; 



(d) determine the shoaling characteristics of the 

 deepened outer bar part of the jetty channel; and 



(e) determine the best locations for additional anchor- 

 age areas within the jetty channel or in Bolivar Roads. 



(7) The Model . The Galveston Harbor model was a scale repro- 

 duction of a 174.5-square mile area which included a small part of 

 Galveston Bay and a much larger part of the Gulf of Mexico (Fig. 7-16). 

 The Gulf of Mexico part extends 8 miles to the north of the north jetty, 

 6.5 miles to the south of the south jetty, and offshore to about the 

 50-foot depth. 



A movable-bed model was used to reproduce the critical area under 

 study. An analysis of the scaled-down forces available to move sediment 

 in the model indicated that the movable bed should be molded of crushed 

 coal. This material was of proper weight to permit movement and deposi- 

 tion in the model by the model hydraulic forces in a manner similar to 



506 



