FUNCTION AND RESTRICTION OF THE MODE OF STORING CLEAR WATER AND DISCHARGING MUDDY FLOW OF SANMENXIA RESERVOIR

摘要

Since the year of 1974 Sanmenxia (hereafter referred as SMX) reservoir has adopted the operation mode of storing clear water and discharging muddy flow. Up to 1985 the reservoir kept a relative equilibrium of erosion and deposition and relative stability of Tongguan (hereafter referred as TG) elevation and preserved a certain effective storage capacity. Meantime, SMX reservoir has played an important role in flood control, irrigation, power generation, etc. But since 1986 the oncoming water and sediment load has reduced greatly especially the water amount during the flood season. The reduction in water has been expressed mainly by the reduction of flood times and flood peaks. Intensive scouring in the area of SMX reservoir and great lowering of TG elevation usually take place during flood periods especially during floods from the Weihe River. The amount of water in flood seasons is the basis of the operation mode of storing clear water and discharging muddy flow for SMX reservoir. It is also a basic condition for the equilibrium of erosion and deposition in SMX reservoir and relative stability of TG elevation. Under the condition of extremely low flow years, reservoir sedimentation cannot be avoided even this operation mode is adopted. The more deposition takes place in non-flood season, the more erosion in the following flood season. So the relative stability of TG elevation and the equilibrium of erosion and deposition of the reservoir depend on the compatibility of pool level operated in non-flood seasons with the conditions of flow and sediment load during flood seasons. In addition, regulating flood and sediment load reasonably by SMX reservoir can reduce the rate of aggradation in the Lower Yellow River.