c. Navigation Conditions — Umpqua River Estuary . 



(1) Project . Improvement of navigation conditions in existing 

 navigation channel. 



(2) Reference . Fisackerly (1970). 



(3) Laboratory . WES. 



(4) Test Period . October 1965 to May 1968. 



(5) Problem . An adverse crosscurrent existed in the entrance 

 area. No actual measurements of the crosscurrent were available, and 

 only a general description of the phenomena was provided by tug skippers. 

 Barge tow crossings over the entrance bar are usually made on the flood 

 tide. A barge proceeding seaward in the channel on the south side of the 

 entrance encounters a shear current to the north near the seaward end of 

 the training jetty which forces the tug or barge onto the middle grounds. 

 The Umpqua River entrance is shown in Figure 3-53. 



(6) Purpose of Model Study . Model tests were conducted to obtain 

 an optimum layout of the entrance area jetty system to (a) improve current 

 patterns in the entrance from the standpoint of navigation, and (b) mini- 

 mize the cost of maintenance dredging. 



(7) The Model . The model (see Fig. 3-1) was constructed to lin- 

 ear scales of 1:300 horizontally and 1:100 vertically, was about 280 feet 

 long, 100 feet wide at its widest point, and covered an area of about 

 10,000 square feet. The model was a combination fixed- and movable-bed 

 model which was initially constructed as a fixed-bed model, with provi- 

 sions to later convert the entrance area to movable bed if necessary. 



(8) Test Procedures . Crosscurrent observations were obtained 

 by means of time-exposure photos of a staff- type float, weighted so that 

 the bottom was 10 feet below the water to represent the depth of a loaded 

 oceangoing barge. 



(9) Summary of Test Results . In the model, a crosscurrent was 

 created by generating waves which approached from the northwest quadrant. 

 Waves approaching from that direction tended to pile up water in the angle 

 between the south jetty and the training jetty, resulting in a head dif- 

 ferential between this area and the navigation channel which generates the 

 crosscurrent. The condition is accentuated during the flood phase of the 

 tide, because a part of the tidal flow naturally enters into the angle 

 between the jetties, and the outflow from the angle must turn more than 

 90° to flow upstream in the main channel. 



Photos of the crosscurrent for existing (base test) conditions and 

 for three of the various plans tested are shown in Figure 3-54. Elimi- 

 nation of the angle between the south and training jetties by extending 

 the training jetty to the outer end of the south jetty (plan 1 in Fig. 



137 



