After numerous tests, it was determined that a chain of disposal islands, 

 generally following the east side of the navigation channel and with sub- 

 stantial openings between adjacent islands (Fig. 3-58), would neither 

 result in adverse effects on circulation patterns nor cause undesirable 

 crosscurrents in the navigation channel. In the area between Matagorda 

 Peninsula and a point about opposite Port O'Conner, the disposal islands 

 had to be oriented so that the long axes were parallel to the predominant 

 current directions; this increased the widths of openings between adjacent 

 disposal islands to prevent further restriction of the entrance to the bay 

 and the production of crosscurrent velocities and patterns which might be 

 detrimental to navigation (Fig. 3-59). 



f . Submerged Disposal Areas — James River . 



(1) Project . Evaluation of existing open-water disposal areas 

 adjacent to 35-foot-deep navigation channel. 



(2) Reference . Boland and Bobb (1975). 



(3) Laboratory . WES. 



(^"^^ Test Period . March 1969 to September 1970. 



(5) Problems . For a number of years the U.S. Army Engineer 

 District, Norfolk, has been using the open-water disposal technique to 

 dispose of material dredged during maintenance of the existing James 

 River navigation channel extending from deep water in Chesapeake Bay 

 some 100 miles to the city of Richmond, Virginia. It was necessary to 

 determine if the areas used for disposal between Newport News and Hope- 

 well were performing satisfactorily in terms of retaining the placed 

 dredged material and to obtain some idea of the life expectancy of the 

 respective areas. 



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

 mine if the areas used for dredged-material disposal were performing 

 satisfactorily and to determine their life expectancies. Alternate 

 disposal areas were evaluated as necessary. 



(7) The Model . The existing James River model was used (see Fig. 

 3-48). Adjustment of the model to reproduce prototype tides, currents, 

 and salinities was accomplished before conducting the study, and no addi- 

 tional adjustment for this purpose was required. However, shoaling veri- 

 fication in the problem area had not been accomplished, and tests were 

 conducted to demonstrate the capability of the model to reproduce known 

 prototype shoaling characteristics. Gilsonite was selected as the appro- 

 priate model sediment. 



(8) Test Procedures . The tests involved placement of lightweight 

 sediments (gilsonite) in the disposal areas, tracing patterns of movement 

 from such areas, and defining the areas where sediments moving from the 

 disposal areas would deposit. If the test results indicated a probable 



146 



