The model was initially constructed as a fixed-bed model throughout; how- 

 ever, provisions were made to convert the entrance area to a movable-bed 

 model at a later date to investigate the effects of various plans on bed 

 configuration in the entrance. The primary tide generator was located 

 in the model ocean, and a secondary tide generator reproduced the proper 

 ebb and flood discharges at the upstream end of the model, since the 

 tidal influence extended about 50 miles beyond the upstream model limit. 



C8) Test Procedures . The model was operated with saltwater and 

 freshwater for all fixed-bed tests. Since the sediments in the lower 

 Columbia River Estuary consist primarily of fine sand with a grain size 

 of 0.15 to 0.3 millimeter, a granulated material was used as the fixed- 

 bed model shoaling material. Shoaling test techniques were developed by 

 trial and error at each of the seven problem areas investigated rather 

 than developing a single comprehensive testing procedure for the entire 

 model. In each case it was determined that polystyrene (S.G. = 1.08) was 

 the most appropriate material. 



(9) Summary of Test Results . The test results indicated that 

 rehabilitation of the existing outer end of the south jetty would not 

 significantly benefit the hydraulic, salinity, or shoaling characteristics 

 of the entrance area as a whole, although some additional protection to 

 vessel traffic from ocean wave action would probably be effected by the 

 rehabilitation. However, the tests also indicated that, if the seaward 

 1,900 feet of the above-water part of the jetty (Fig. 3-42) were allowed 

 to degrade to an elevation of about -15 feet MLLW, shoaling of the en- 

 trance channel could be reduced by about 21 percent (Fig. 3-43). This 



20 



40 



60 



80 100 120 140 



lOO-FT CHANNEL STATIONS 



220 



Figure 3-43. Effects of south jetty plan 2 and jetty B on Columbia 



River entrance shoaling (after Herrmann, 1974; Herrmann 

 and Simmons, 1966). 



28 



