[Calculation of environmental flows in river reaches based on ecological objectives]

Based on the identifying the ecological objectives, environmental flows in river reaches is calculated after the relation between parameters of objectives, and river discharges is determined. The ecological objectives are determined in a two step process: theobjective will be determined for the critical period of the year, then the temporal variation will be defined. Considering the compatibility between the different kinds of environmental flow requirements, the strictest objective is settled to be the ecological objectives for the critical period of the year. The temporal variation of the natural river discharge monthly is settled to be the temporal variation of ecological objectives. In the studies of the environmental flows in the river reaches downstream for Guanting reservoir in the Yongding River of Haihe River Basin, the requirements of velocities for spawning of the fish in April are regarded as the ecological objectives in the most critical period because this also is the period of highest water demand for irrigation. The relation between objectives and river discharge is identified using historical data at the river station. The results indicate that the minimum, medium and ideal lever of annual environmental flow requirements are 1.56 x 10(8) m3, 5.97 x 10(8) m3 and 11.02 x 10(8) m3, about 7.19%, 27.51% and 50.78 % of the natural river discharge respectively. The ratio of water requirements monthly should be 20 % in the flood period (Aug.) and be 20% in biological propagation period in spring (Apr. - Jun.).