Figure 3-42. Columbia River entrance (after Herrmann 

 and Simmons, 1966; Herrmann, 1974). 



5 miles, and the average annual maintenance dredging amounts to about 

 2.3 to 2.5 million cubic yards. A 5,30Q-£oot-long jetty B CFig- 3-42) 

 was authorized for the Columbia River entrance to reduce maintenance 

 dredging in the entrance channel. The Wauna-Lower Westport Bar (Fig. 

 3-5) is located between river miles 41 and 45 on the Columbia River and 

 is considerably upstream from the extent of saltwater intrusion. For the 

 35- by 500-foot channel, the average annual maintenance dredging was 

 about 315,000 cubic yards. Model tests were made to determine the changes 

 in hydraulic and shoaling characteristics that would be effected by en- 

 larging the channel to 40 by 600 feet and to develop an optimum improve- 

 ment plan to minimize the cost of maintenance dredging in the enlarged 

 channel. 



(6) Purpose of Model Study . The model study was conducted to 

 determine: (a) the need for and to develop optimum plans for rehabilita- 

 tion of existing entrance jetties, (b) the most effective means of reduc- 

 ing the cost of maintenance dredging in the navigation channels, and (c) 

 the effects of the proposed interior channel enlargement from 35 by 500 

 feet to 40 by 600 feet. 



(7) The Model . The Columbia River Estuary model reproduced the 

 lower 52 miles of the estuary (see Fig. 3-5) and was constructed to lin- 

 ear scales of 1:500 horizontally and 1:100 vertically. The model (a com- 

 bination fixed- and movable-bed type) was about 560 feet long, 130 feet 

 wide at its widest point, and covered an area of about 48,000 square feet. 



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