Pilot field implementation of suction dredging for sustainable sediment management of dam reservoirs

The buildup of sediment deposits in reservoirs is a long-standing problem with serious consequences on the reservoirs' functionality and the ecology of their river systems. In the last two decades, hydraulic dredging has been used as a more viable engineering solution to restore reservoirs' sustainability. This study proposes a novel ejector-pump dredging system (EPDS) that solely utilizes hydraulic dredging for removal and transport of the sediments deposited at the reservoir's bed. Unlike conventional dredging methods, air is injected into the header pipeline to create a turbulent three-phase flow regime that enhances the solids suspension and continuous flow in the system. Introducing air effectively reduces the critical value of the deposition velocity of the dredged solids and transports them in a slug flow regime. This technique minimizes the tendency of the sediment to settle, and therefore eliminates system plugging. A laboratory prototype of the proposed system has proven the efficacy of removal and transport of mixed-size sediments up to 150 mm. Field trials have further shown the feasibility of the proposed system. Removal of large sediments with productivity approaching 70 m3/h was made possible using the suction-type EPDS. The hopper-type EPDS enabled carrying the dredged material for up to 1,000 m without resorting to a booster pump. The developed system was successfully used as part of an integrated dredging management program carried out for the Oouchibaru, Saigo, and Yamasubaru dams in the Mimi River basin, Japan. The very low turbidity levels recorded during the sediment dredging and transport operations of EPDS are indicative of the eco-friendly performance of the system.