Ecological Flow Calculation And Simulation Of Ecological Scheduling Based On The Different Degree Of Water Resources Development And Utilization

Ecological flow is the powerful guarantee for maintaining the ecological function and health of rivers.In this paper,taking the main stream basins of Daxia river and Xida river with different degrees of water resources development and utilization as the typical research areas,it is used that the Set Pair Analysis method,IPTA method and Extreme-Point Symmetric Mode Decomposition to analyze the spatial variation characteristics,time change trends and mutation points of runoff,and the hydrological methods and ecological hydraulic methods are adopted to calculate the ecological base flow,ecological flow during sensitive periods and self-net flow in the main stream of Daxia river,and comprehensively analyzes and determines the ecological flow,early warning value and ecological scheduling scheme of the control section.Based on MIKE21 software,the change process of outlet flow at head works in Xida river is simulated,the ecological base flow and ecological flow threshold during the sensitive period are calculated.The ecological scheduling model in water supply area of Xida river reservoir is also constructed,and the non-dominant sorting genetic algorithm is applied to compute the ecological scheduling process of Xida river reservoir under the scenario of optimal development of water resources at different frequencies in 2025.The reasonable ecological water volume target value is proposed to be suitable for the phased ecological restoration purpose in Xida river.The main conclusions are as following:(1)The runoff in the main streams of Daxia river and Xida river is unevenly distributed within the year,and the inter-annual variation is large.Xiahe,Shuangcheng and Zheqiao stream stations in Daxia river are all more than 0.6,and there is synchronization in the spatial variation of annual runoff.The maximum trend lengths of monthly runoff at Xiahe,Shuangcheng,and Zheqiao stations are 0.2483×10~8 m~3,0.6702×10~8 m~3,and 0.8058×10~8 m~3 respectively.The maximum monthly runoff variation occurs in October and November.The maximum trend lengths of monthly runoff at Xida river reservoir station is 0.1393×10~8 m~3,and the maximum monthly runoff change occurs in September and October.The annual runoff of Daxia river changed abruptly in 1967 and 1973,and that of Xida river changed abruptly in 1964and 1974.(2)Based on the ecological base flow,ecological flow in sensitive period and outsourcing line of self-purification flow calculated by Q_p method,the eco-hydraulics method and improved PHABSIM method,the basic ecological flow at Xiahe,Shuangcheng and Zheqiao sections in Daxia river is determined to be 2.28?5.00 m~3/s,6.42?8.60 m~3/s,8.29?9.84 m~3/s.The analysis of ecological flow surplus at section shows that Xiahe section in Daxia river has an ecological flow deficit for 76 months from 1992 to 2008,the maximum ecological flow deficit is 3.09 m~3/s.That of Shuangcheng section is 34 months from 1973 to 2016,the maximum ecological flow deficit is 5.90m~3/s,and the ecological flow is in good condition.That of Zheqiao section is 41 months from 1992 to 2003,of which the maximum ecological flow deficit is 8.38m~3/s.From 2010 to 2019,the daily satisfaction degree of ecological flow at Xiahe and Zheqiao section is 59.73%to 96.99%and 80.27%to 100%.Compared with 2000 to2009,the daily satisfaction degree is significantly improved,and the ecological flow in river is better guaranteed.(3)The discharge flow 2.77 m~3/s between head works in Xida river and Xinzhuangzi section can produce the continuous water surface,and the discharge flow is 3.92 m~3/s,can meet the water requirements of aquatic organisms in the river.The ecological based flow and its thresholds in the sensitive period are 2.77 m~3/s and 3.92m~3/s.(4)In the planning level year of 2025,under the condition of ensuring the ecological flow,the water supply area of Xida river reservoir will have different degrees of water shortage under the current development,development priority,ecological priority,and balanced development scenarios.Taking the water use model of balanced development scenario as the ecological scheduling plan,under the incoming water frequency conditions of P=10%,P=50%,P=75%,and P=95%,the outlet volume at head works in Xida river is 6526×10~4 m~3,1168×10~4 m~3,844×10~4 m~3 and 595×10~4 m~3,as the ecological water volume required for the purpose of ecological restoration in Xida river.