Hydro-Induction Sediment Discharge Technique for Preventing Sedimentation in Hydropower Dams

Abstract

Hydro-induction sediment discharge technique (HSDT) aims to prevent reservoir sedimentation by withdrawing the discharge water from the reservoir bottom to suck up and discharge sediments, and by inducing vertical vortexes and undercurrents in the reservoir bay to keep sediments agitated and moving. The technique is facilitated with a n innovative discharge conduit system having bottom intakes that are engineered and configured to suit individual dam situation for maximum process efficacy. Analyses of the hydraulics and operating principles of the bottom intake discharge system are presented. Guidance for designing and configuring the discharge conduit system is provided. Several key issues concerning the practical application of the technique are discussed briefly. The process feasibility and functionality of the bottom intake discharge system have been demonstrated with a small test setup. Testing with large scale models and field tests are needed to develop design data for big dam application. For hydropower dams having power plants at or by their toes, the appurtenant setups for releasing the reservoir water to the power generators are all similar. They all provide the water release gates at about just below the reservoir’s lowest operating water level with some kind of valve to stop or regulate the water flow. The discharge water then flow down the penstock to the generator. This text book arrangement has been followed for decades and accepted as a golden model by hydropower dam engineers all over the world. A major problem with this traditional arrangement is the deposition of sediments in the bottom of the dam reservoirs, especially for those with influents carrying large amount of sediments. Sedimentation occurs as the influent flow diverges and slows down upon entering the reservoir causing sediments to deposit and accumulate in the reservoir bottom. The process continues until the bed of the reservoir reaches a steady state slope at which point all the sediments carried by the influent water would be moving right through the reservoir and carried away with the effluent water. At this stage, unfortunately, the reservoir would have lost most of its usable storage capacity and its capability for flood control. Detention of soils and sediments in large reservoirs also causes degradation of downstream farmlands and flora as well as erosion of downstream riverbed. Organic wastes released to upstream river are also trapped in the deep water of the reservoir to possibly cause serious detrimental effects to fish life.