Hydraulic suction dredging efficiency study for Wushe Reservoir

Constructed in 1959, Wushe Reservoir is situated in the upper reaches of the Zhuoshui River in Ren’ai Township, Nantou County, Taiwan. By 2023, sedimentation had filled approximately 80.88% of the reservoir’s total storage capacity. To mitigate this issue and preserve the reservoir’s functionality, a comprehensive sediment management strategy was initiated in 2016 by the Taiwan Power Company. This strategy incorporated two primary sediment removal techniques: hydraulic suction dredging (600,000 m³/year) and a sediment bypass tunnel (SBT) system (750,000 m³/year). This paper focuses on the design and performance evaluation of hydraulic suction dredging, based on numerical hydraulic simulations and physical model testing. The dredging system was designed to operate at a flow rate of 0.25 m³/s with a sediment concentration of 200,000 ppm. The excavated sediment is temporarily stored in two downstream deposition areas and is subsequently flushed out during flood events. Modeling and field tests indicate that the first temporary deposition site, located at the plunge pool of the SBT, achieves a scouring efficiency of 67% ~ 89%, while the second site, located further downstream, exhibits efficiencies ranging from 77% ~ 89%. One-dimensional hydraulic modeling confirms that integrating SBT operations with hydraulic dredging mitigates riverbed scour. The study demonstrates that both temporary sediment placement zones are viable and contribute to effective sediment conveyance from the reservoir to the estuary, maintaining riverbed stability.