Study Of Drought-Limited Water Level Of Reservoir In The Large-Scale Irrigation District Based On Systems Simulation And SPA

With the development of economy and society and the change of climate conditions,regional drought is becoming more and more serious,and reservoirs are playing an increasingly prominent role in the process of drought relief and disaster reduction.The proposal and application of drought-limited water level is of great significance for scientific play of regulating and controlling role of large and medium-sized reservoirs in drought resistance and alleviation of drought situation in river basin.The overall operation effect of water resource system was not considered in the optimization of drought-limited water level of reservoir in irrigated area and drought-resistant water supply measures are empirical at present.In this paper,a new method of optimum determination of drought limit water level is proposed.Based on the initial drought-limited water level determined by the water supply process,combined with urban and rural water supply,agricultural irrigation,hydroelectric power generation,ecological environment and other factors,a comprehensive evaluation model of water resource system operation effect of reservoir irrigation area based on fuzzy set pair analysis method was established.Based on the simulation model of water resources system in the reservoir irrigation area,the optimal objective of comprehensive operation level of water resources system was established,and the immune genetic algorithm(IGA)was used to optimize the drought-limited level and proportion of irrigation water supply restrictions.Taking Meishan Reservoir in Shihe Irrigation area as the object,the case study was carried out and the impact analysis of drought-limited water level was conducted.The main results are as follows:(1)Based on the fuzzy set pair analysis system evaluation method,the optimal drought-limited water level of Meishan Reservoir and irrigation water supply restriction strategy is obtained.The drought warning water level is divided into three sections:115.2m from October to February of next year,117.2m from March to April and July to September,and 119.2m from May to June.The drought depleted water level is divided into two sections:112.1m from July to April of next year,114.3m from May to June.According to the inflow combination,the irrigation water supply restriction strategy can be divided into three groups:median-dry,rainy-dry/median-dry and dry-dry.(2)Using the simulation model of water resources system in the reservoir irrigation area,the comprehensive operation effect of the reservoir water resources system with or without drought limit water level is compared.The results show that compared with the optimal drought-limited water level with economic benefit as the single goal,the performance index of Meishan Reservoir has been greatly improved.Among them,the economic benefit of Meishan Reservoir has been increased by 460,000 yuan,the water amount provided to the reverse regulating reservoir has been increased by 5.55 million m~3,and the abandoned water amount has decreased by 5.66 million m~3.The water supply of pond dam in Shihe irrigation area increased by 2.53 million m~3,while crop yield reduction rate decreased by 3.32%.(3)The drought risk assessment model of water resources system was established to analyze the drought risk of water resources system under different control methods.The results show that the drought risk indexes are improved in different degrees under the control of drought limit water level considering the inflow situation,and the improvement degree of drought risk in single year is slightly better than that in consecutive years.(4)The risk of rice yield loss due to drought in Shihe irrigated area was calculated by using the quantitative risk assessment model of drought loss.The results showed that the expected yield reduction rate of rice due to drought was reduced by 3.15%when the water supply restriction strategy considering the characteristics of reservoir inflow and crop growth was included in the control system of drought limit water level,which provided strong support for the smooth implementation of drought limit water level and drought resistance of agricultural irrigation in drought period.This study shows that the application of system simulation and comprehensive evaluation decision method is beneficial to improve the comprehensive operation effect of the reservoir irrigation area system,improve the utilization efficiency of water resources and economic benefits of the reservoir irrigation area,and provide strong support for the application of drought-limited water level and drought resistance of agricultural irrigation in the drought period.