Study On The Ecological Water Requirement And The Effect Of Water Regulation On Water Quality And Fish Habitat Of Yitong River

In the northern region of China the water resource is short and this causes the contradiction between the reservoirs' benefit and the ecological function.In dry seasons,the reservoir impoundment will cause that there is no adequate supply of water in the lower reaches of the river.The river flow of the reservoir downstream is slow,or even there is no flow.The ecological water demand of the river cannot be satisfied for a long time and a series of ecological problems will happen.In order to improve this situation,scheduling supply flow on the reservoir's downstream river should be done.The study object of this article is the Changchun city reach of Yitong River.First,the Tennant method is used to calculate the basic flow of the river,also considering the water surface evaporation demand,leaking water requirement and river green belt and farmland water demand.Then calculate the total annual ecological water requirement of the study area and April to October(break-up period)monthly ecological water requirement.The calculation results show that in the study area the total amount of ecological water demand is 0.8314?108m3 and the ecology water requirement in the outside the river account for 77% of the total water requirement in the study area.Comprehensively considering the factors such as precipitation,water-collecting amount and the average annual run-off in the upper reaches of the study area,this study proposes the flow scheme of XinLicheng Reservoir,based on ecological water demand in the downstream.The April to October(break-up period)monthly ecological water requirement is 0.61?106m3,1.11 ?106m3,1.67 ?106m3,4.02?106m3,4.69?106m3,1.18?106m3 and 0.36?106m3.The MIKE11 one dimensional hydrodynamic water quality model and PHABSIM physical habitat simulation model were used to understand the change of water quality,water and physical habitat in the study area after the flow scheme implementation of Xin Licheng Reservoir.The results of calibration and validation of one dimensional hydrodynamic water quality model in MIKE11 is very good.The correlation coefficient R2 is greater than 0.95.This shows that the MIKE11 model has a certain reliability and accuracy in the simulation of hydrodynamic and water quality of the river,so this model can be used to simulate the river in the study area.Using MIKE11 model to simulate the city reservoir adjusting flow,the results shows that the ecological adjusting flow can effectively reduce the concentration of COD and ammonia nitrogen in the middle and lower reaches of the river,with the sewage outfall trapped and the pollution load reduced on both sides of artificial rive in the study area.During the implementation,the concentration of COD in rivers can be maintained at 20-30mg/L and the ammonia concentration can be maintained at 3-4mg/L.This study uses the physical habitat simulation model,PHABSIM,to obtain the habitat suitability index of the target species(common carp)in the river channel.Then the Q-WUA relationship of the target species(common carp)in the reach of the study area was calculated.This Q-WUA relationship shows that,when the flow is 1.578m3/s,the available physical habitat of the target species(common carp)is the largest in April to September,with an area of 3.1?103 ?/km.According to the simulation results of the MIKE11 model,the ecological flow can keep the flow in the range of 0.6-1.5m3/s in the river downstream in April to September.The physical habitat area of the target species(common carp)can be maintained at between 1.25?103 ?/km-3?103 ?/km in April to September.Therefore,the results of this paper show that adjusting flow,based on the ecological water demand,can effectively reduce the concentration of pollutants in the downstream of the river,and increased river physical habitat area.The ecological environment of the river basin can be improved.