| Due to the dual effects of climate change and human activities,the incoming water in the upper reaches of the Yongding River has been decreasing year by year,and the ecological environment in the lower reaches has gradually deteriorated.The river in the plain area has been continuously cut off,and a large number of organisms that rely on the aquatic environment have lost their living environment.The species diversity has decreased,the river’s storage function has decreased,and the self-purification ability has weakened,which has aggravated the flood disaster and water quality deterioration of the river.Coupled with the unreasonable development and utilization of water resources,the Yongding River has lost its original water conservation function,which has seriously affected the regional water resources security and water ecological environment quality,and restricted the coordinated development of Beijing,Tianjin and Hebei.In order to restore the Yongding River to a "flowing river,clean river,green river,and safe river",the ecological water replenishment project in the Yongding River basin was officially launched.The ecological water replenishment project of Yongding River is first replenished by Sanggan River and Yanghe River to Guanting Reservoir,and then operated by Guanting Reservoir to Beijing section of Yongding River.In view of this,this paper takes the ecological water replenishment project of Yongding River as the research object,and studies the ecological water replenishment of the upper and lower reaches of Guanting Reservoir and the ecological operation of Guanting Reservoir.Firstly,the ecological water demand process in the downstream channel of Guanting Reservoir is calculated under the premise of considering runoff variation.On this basis,the ecological operation model of Guanting Reservoir is established,and the satisfaction of the discharge of Guanting Reservoir to the ecological water demand in the downstream river channel and the competition law of ecology and power generation objectives are discussed.Secondly,the MIKE 11 HD model was used to establish a one-dimensional hydrodynamic model for the ecological water replenishment of the upper and lower reaches of the Guanting Reservoir.On this basis,the upstream and downstream ecological water replenishment process of Guanting Reservoir was analyzed.Finally,the hydrodynamic model is coupled with the reservoir operation model to discuss the satisfaction of ecological water demand in the downstream channel of Guanting Reservoir and the investment cost of water purchase under different scenarios of water diversion from the Yellow River.The storage and discharge process of Guanting Reservoir and the evolution results of downstream flow are obtained,and the water resources scheduling and water conveyance scheme of ecological water replenishment project in Yongding River Basin is formulated.The research results can provide technical support for the inter-basin water transfer of Yongding River and the formulation of ecological water replenishment plan in the basin.It is of great scientific significance to understand the ecological flow restoration process of seasonal rivers in northern China under the influence of inter-basin water transfer.The main research results of this paper are as follows:(1)The variation diagnosis of the inflow runoff sequence of Guanting Reservoir was carried out,and the mutation point of the runoff sequence was determined.The runoff sequence is divided into two stages before and after variation.The hydrological sequence before variation is taken as the calculation sequence of river ecological flow,and the ideal ecological flow process,suitable ecological flow process and minimum ecological flow process in the river channel under the reservoir dam are obtained.(2)Based on the calculation of ecological flow,a multi-objective ecological operation model of Guanting Reservoir(ecological and power generation objectives)was established.The tradeoff relationship and conversion trend between the satisfaction of the reservoir discharge to the river ecology and the two objectives of ecology-power generation were obtained,that is,the power generation and the average ecological guarantee degree showed a nonlinear negative correlation,highlighting significant stress and competition.The conversion relationship between the two was 0.0196(108kW·h):1(%).(3)According to the trend analysis of the runoff data of Guanting Reservoir for many years and the calculation of the ecological operation of Guanting Reservoir,it is found that the incoming water in the upper reaches of Yongding River is decreasing year by year,the ecological environment in the lower reaches is gradually deteriorating,and the ecological guarantee rate is seriously small.It is urgent to carry out ecological water replenishment projects to ensure the ecological water volume of Yongding River Basin.(4)MIKE 11 software was used to establish a one-dimensional hydrodynamic model for the main rivers in the Yongding River Basin,and the model was calibrated and verified.According to the calculation results of the judgment index,it was proved that the model simulation constructed in this paper had good accuracy and the error was within the controllable range.The model parameter values can well reflect the actual situation of the river section and can be used for the study of river ecological water replenishment.(5)The process of ecological water replenishment in the upper and lower reaches of Guanting Reservoir was analyzed,and the amount of water replenishment,loss,evaporation,storage and leakage in each river section were counted.The water delivery efficiency of the river section during the ecological water replenishment period and the average loss rate of the ecological water replenishment were calculated.In the spring of 2020,the average loss rate of ecological water replenishment in the upper reaches of Guanting Reservoir ranged from 1.35%to 6.90%/10 km,and the average loss rate of ecological water replenishment in the lower reaches ranged from 0.75%to 27.88%/10 km.(6)The coupling model of hydrodynamic and ecological operation in the upper and lower reaches of Guanting Reservoir was established and solved,and the flow fitting function between different sections during the ecological water replenishment period in the upper and lower reaches of Guanting Reservoir was obtained.The satisfaction of ecological water demand in the downstream channel of Guanting Reservoir and the investment cost of water purchase under different scenarios of water diversion from the Yellow River was discussed,and the storage and discharge process of Guanting Reservoir and the evolution results of downstream flow were obtained.Finally,the water resources scheduling and water conveyance scheme of the ecological water supplement project in Yongding River Basin was formulated. |
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