THE OPERATION MODE OF “STORING THE CLEAR WATER AND DISCHARGING THE MUDDY FLOW” FOR RESERVOIRS BUILT ON HEAVILY SILT-LADEN RIVERS——A CASE STUDY OF THE SANMENXIA RESERVOIR

Observation of the operation of the Sanmenxia Reservoir on the Yellow River has led to the conclusion that to preserve a certain effective storage volume for reservoirs built on heavily silt-laden rivers is feasible if the reservoir is operated according to the principle known as“storing the clear water and discharging the muddy flow”. The relative stability of the bed elevation at the end of the backwater and the reservoir‘s erosion and deposition equilibrium depend on the compatibility of the pool level maintained in non-flood seasons with the conditions of flow and sediment load during flood seasons. Operating the reservoir to regulate the flood and sediment load during flood seasons can reduce the rate ofaggradation in the Lower Yellow River. The basic condition for applying the operation mode of “storing the clear water and discharging the muddy flow” is that a sufficient amount of water should be used for discharging sediment during flood seasons. Under the condition of extremely low flow years, reservoir sedimentation cannot be avoided even if this operation mode is adopted.