Multi-objective Dispatching Of Linjiacun Reservoir Considering River Hydrological Health And Water Supply Risk Analysis

Climate change and human frequent high-intensity activities aggravate the contradiction between supply and demand of water resources in the region,but also severely restrict the healthy development of river hydrology and ecology.Considering the potential water supply risk of reservoir dispatching caused by the wetness–dryness encounter uncertainty of precipitation in irrigation area and upstream runoff,it poses a threat to food security in irrigation area.Therefore,this paper takes the Linjiacun Reservoir in Baojixia as the research object,starting from the connotation of river hydrological health,takes the minimum ecological water spill and shortage in the section of Linjiacun in Weihe River as the ecological target,the maximum power generation benefit of Linjiacun Hydropower Station and the maximum irrigation benefit of irrigation area as the power generation and irrigation objectives,establishes the multi-objective optimal dispatching model of reservoir groups to assess the river hydrological health.Establishing the joint probability distribution of precipitation in irrigation area and upstream runoff,and analyzing the characteristics of runoff and precipitation encountering changes;To evaluate the risk of water supply for reservoir operation under uncertainty of precipitation and runoff,in order to provide theoretical basis for reservoir operation and management in irrigation area.This study draws the following main conclusions.(1)To carry out analysis on annual precipitation change process in irrigation area and upstream watershed of Linjiacun section,to identify annual variation regularity and distribution characteristics of runoff process in Linjiacun section,to analyze and calculate runoff from canal head to reservoir and precipitation frequency in irrigation area;Calculate agricultural irrigation water demand in irrigation area according to crop water demand and irrigation quota;The ecological water demand was calculated by improved Tennant method and 7Q10 method.(2)The multi-objective dispatching model of Linjiacun Reservoir is constructed with the objectives of minimizing ecological water spill and shortage,maximizing power generation benefit and maximizing irrigation benefit,and is optimized by NSGA-III-DE algorithm.There are restrictive relationships among reservoir power generation,irrigation and ecological objectives,and the competition becomes fierce with the decrease of water inflow.Constructing the TOPSIS model based on cooperative game theory and select the dispatching result with the greatest comprehensive benefit.The ecological flow threshold for evaluating river hydrological health index is determined.Irrigation diversion in irrigation area is likely to have adverse effects on river hydrological health.However,reasonable control measures can effectively alleviate the contradiction between water supply and demand in irrigation area and improve river hydrological health level.(3)The weak correlation between precipitation in irrigation area and upstream runoff results in the wetness–dryness encounter uncertainty.It is considered that the best edge distribution function of precipitation and runoff series in irrigation area is lognormal distribution,and Clayton copula is more suitable for estimating the joint distribution of precipitation and runoff.The joint distribution probability and actual probability of 9different scenarios of precipitation and runoff are calculated and analyzed.The joint distribution probability of dry precipitation and runoff scenarios(D-D)is 22.32%,which is the largest in all scenarios,and the probability of imbalance between supply and demand of water resources is greater.(4)A multi-objective reservoir dispatching model with the objectives of minimizing water shortage,maximizing economic benefits and minimizing ecological spill and water shortage in agricultural irrigation was established.The trade-off among the three dispatching objectives is comprehensively considered,in which there is obvious compatibility between water shortage in agricultural irrigation and economic benefits,and there is mutual restriction between economic benefits and ecological water spill and shortage.The VIKOR model with comprehensive weighting based on cooperative game is constructed to make multi-criteria decision.The optimal scheduling results are R104,R116,R66,R95,R5,R28,R117,R89 and R110 respectively.The change characteristics of different precipitation and runoff encounters can be fully displayed by the dispatching schemes set according to nine rainy and dry encounter scenarios,which verifies the rationality of the schemes.An evaluation index system for water supply risk was established,which consists of monthly irrigation probability,total water shortage rate of irrigation,risk rate of insufficient economic benefit and risk rate of insufficient ecological basic flow.With the decrease of available water and the increase of water demand,the risk of water supply for reservoir operation increases gradually.Category A and Category B are mainly exposed to medium and low water supply risks with a joint distribution probability of 62.5% and that of Plan C is higher with a joint distribution probability of 37.5%.Among them,C3 scheme is extremely short of water,with the highest probability of joint distribution of 22.32%,and the highest risk of water supply is grade V.