Evaluation of the Submerged Discharge of Dredged Material Slurry During Pipeline Dredge Operations

This report describes a study conducted to investigate the feasibility of using submerged discharge to control the turbidity generated when a pipeline dredge discharges a fine-grained dredged material slurry into open water. The program included a survey of field practices, literature survey, analytical investigations, and numerous flume tests. The experimental investigation was performed at reduced scale in an 8-ft-wide by 32-ft-long by 2. 5-ft-deep test tank that was specially constructed for the program. Two series of tests were run one in which a simple open pipe discharged dredged material slurry underwater and a second in which four different types of discharge processors, designed to reduce the discharge momentum, were tested and evaluated by comparing their performance with that of the open pipe. The influence of the following system parameters was examined water type sediment type bottom type solids concentration and discharge velocity, angle, diameter or area, and height above the bottom. The results of the experimental program demonstrated that striking reductions in turbidity can be realized with a submerged discharge processor that diffuses the flow, minimizes entrainment, and discharges the dredged material slurry close to the bottom. The proposed design incorporates a conventional conical diffuser and a radial discharge section.