Research On Optimal Allocation Of Water Resources In Ecological Irrigation Districtbased On SD-MOP Model

Irrigation district is an important base for agricultural production in China,providing material support and guarantee for the sustainable development of agriculture,economy and food security.The traditional irrigation districts have the main goal to improve the interests of irrigation districts,ignore the problems of excessive resource consumption and serious environmental pollution brought by the interests.With the construction of ecological irrigation districts with the theme of“resource conservation,high yield,high efficiency,and ecological and environmental health”,through rational development and allocation of water resources.The internal dynamic balance of the irrigation district system is maintained and improved,and the subsystems are interdependent and mutually promoted to make the irrigation district water resources sustainable use,a virtuous cycle of the economy,and ecological self-healing.The research on optimal allocation of water resources based on the concept of ecological irrigation district has important guiding significance and practical value for improving water use efficiency,promoting sound development of irrigation system,achieving sustainable use of irrigation water resources,maximizing social and economic development,and controlling ecological environment deterioration.This paper constructs the concept of ecological irrigation district with the goal of“resource conservation,high production,high efficiency,and good ecological environment”,and carries out research on optimal allocation of water resources in irrigation districts.Taking the Jinghui canal irrigation district of Shaanxi province as an example,based on the water-saving-economy-ecological multiple objectives,a System Dynamics-Multi-Objective Programming(SD-MOP)coupling model was constructed to simulate the ecological irrigation district.The causal feedback relationship of each subsystem was carried out to research on the optimal allocation of water resources in ecological irrigation districts,and the following research results were obtained:(1)Identification of agricultural water demand driving factors in irrigation district and their trend analysisMann-kendall test and Sen's slope estimation method were used to analyze the main trends of agricultural water demand in irrigation district.The results showed that the temperature(highest and lowest)and evaporation of the site in the Jinghui Canal irrigation district were increasing;the relative humidity was higher than Gaoling station.In addition to the downward trend of Lintong station,the other two stations showed an upward trend;the wind speed and sunshine hours of each station showed a downward trend;the precipitation decreased except Lintong station,and the other stations all showed a downward trend.The planting structure change in the irrigation area from 1993 to 2009 was not significant,showing a steady trend.The annual variation of crop water demand in meteorological stations in the Jinghui canal irrigation district showed a downward trend,with little difference in space.Grey correlation analysis and principal component regression analysis were used to analyze the impact of environmental changes on agricultural water demand.The results showed that crop acreage,precipitation and evaporation had a greater impact on agricultural water demand in irrigation district.(2)Dynamic simulation of water supply and demand system in ecological irrigation districtBased on system dynamics theory,constructed the subsystem of population,water resources,social economy and ecological environment in irrigation district,analyzed the feedback relationship between subsystems,constructed the simulation model of ecological irrigation district system evolution,identify the sensitive factors of the model,and predicted the different planning level of irrigation district.The supply and demand of water,SD system simulation results showed that the year of flooding(25%)was not lack of water;the year of flat water(50%)was 22 million m~3 in water shortage in 2030,the current year and 2020 were not short of water;dry year(75%)water shortage in the current year,2020 and 2030,the water shortage was 0.06,0.16 and 0.34 million m~3 respectively.Taking water saving and pollution control as the control targets,21 simulation schemes of the current situation,water saving,pollution control and comprehensive types were set up.Scheme 21 was superior to other schemes,the total water demand was reduced by 17.7%,the total nitrogen load concentration was reduced by 10.79%,and the decline rate was higher than the pollution-control single-index regulation scheme.(3)Optimal allocation of water resources in irrigation districtBased on scenario simulation,the threshold of sensitive indicators was defined,and the multi-objective optimization model was solved by interactive multi-objective decision-making with target deviation tolerance.The results showed that the water saving benefit gain was 70%in 2020,the economic benefit gain was 2.38%,and the ecological benefit gain was 8.66%.In2030,the water saving benefit gain was 41.67%,the economic benefit gain was 0%,and the ecological benefit gain was 8.31%.By improving the industry's water use efficiency,reducing the amount of nitrogen fertilizer application,and increasing the river's ecological base flow,the ecological irrigation district will achieve resource conservation,high yield,high efficiency,and healthy development of ecological environment.