plan was adopted, thus saving $4,570,000 in planned jetty rehabilitation. 

 In addition, a substantial maintenance dredging cost savings will result 

 when the jetty has naturally deteriorated to -15 feet MLLW. 



Tests of jetty B indicated that channel shoaling would be reduced by 

 about 28 percent and that the upstream peak in the shoaling distribution 

 pattern would be eliminated (Fig. 3-43). In addition, the structure 

 would cause a very significant change in vertical mixing in the entrance. 

 As a result, middepth and bottom salinities would be generally reduced, 

 while surface salinities would be generally increased (Fig. 3-44). The 

 maintenance dredging savings from this plan would not be sufficient to 

 justify the initial cost of the structure, estimated to be $12 million 

 in 1958. 



The results of the Wauna-Lower Westport Bar (Fig. 3-45) tests indi- 

 cated that enlarging the channel without supplemental improvements would 

 increase the rate of shoaling by about 76 percent and would create a new 

 peak in the shoaling distribution pattern (Fig. 3-46). The best improve- 

 ment plan tested consisted of four pile dikes with lengths of 400 to 

 1,100 feet and three large disposal area fills as shown in Figure 3-45. 

 Model tests indicated that this plan would reduce shoaling in the enlarged 

 channel by about 30 percent and eliminate shoaling in the upstream 2,500 

 feet of the bar (Fig. 3-47). The dikes and fills were constructed in the 

 prototype about 1 year before enlarging the channel. The plan was so 

 effective that new work dredging requirements for the enlarged channel 

 were reduced by 42 percent by the natural scouring action of the newly 

 constructed dikes. Thus, the plan resulted in an initial savings of 

 about $334,000. Future savings will result from the reduced shoaling 

 as compared to an unimproved, but enlarged, channel. 



In 1969, it was estimated that the annual maintenance dredging savings 

 from the south jetty and Wauna-Lower Westport Bar studies would amount to 

 $125,000 (U.S. Department of the Army, 1969). In addition, programed con- 

 struction expenditures of $4,570,000 (south jetty rehabilitation) were 

 saved and an authorized project estimated to cost $12 million (construc- 

 tion of jetty B) was dropped. The total cost of the model study, which 

 included investigations of several other problems, was about $1.2 million. 



b. Environmental Impact of Navigation Channel Enlargement — James 

 River. 



(1) Project . Deepening existing navigation channel from -25 to 

 -35 feet mean sea level (MSL) . 



(1966). 



(2) Reference . U.S. Army Engineer Waterways Experiment Station 



(3) Laboratory . WES. 



(4) Test Period. September 1964 to September 1966. 



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