Research On Water Resources Utilization In Arid Area Oasis Based On Water-soil Ecological Sustainability

Yanqi Basin is located in the north of Bayinguoleng Mongolia Autonomous Prefecture, which is a typical oasis in arid area., due to the excessive exploitation of water-land resources and human activities in oasis in recent years, that cause a series of problems,such as soil salinization,Bosten Lake ecology deterioration, especially the Bosten Lake level has been close to 1045 m. If these problems cannot be solved properly, it will severely restrict the stable and harmonious development of oasis economy-society-ecology system. Therefore, study on water-land resources development, allocate surface water and groundwater rationally in study area, arrange water resources properly for production, living and ecology, promote water resources rational distribution and efficient utilization, which are very important for the water-soil-ecosystem sustainable development,social stability and national unity.Through the analysis of water resources development and utilization in Yanqi Basin, this paper adopts ecological hydrology method to analyze reasonable groundwater depth with multi-angle based on water-soil-ecology safety; furthermore, uses Modflow software to simulate groundwater resources and exploitable quantity in study area; in order to determine the reasonable development model for surface water groundwater in study area, taking the oasis typical area as research object, through the water-salt data analysis in typical area, using the Modflow software and salt balance model to establish "two water" joint development and utilization scheme set, acquire appropriate "two water" development and utilization mode;By using the trend extrapolation and water quota method to forecast water demand in planning level year, taking minimum water shortage and water supply cost as objective function to establish water resources reasonable allocation model based on multi-objective constraint, then using cellular multi-objective particle swarm algorithms to optimize the model;at last, uses lattice theory, ideal solution and water resource carrying index model to evaluate water resources carrying capacity(WRCC) and economic-society development scale in study area; the main conclusion are as follows:(1) Through the analyzation of groundwater depth with vegetation growth, soil salinization and groundwater evaporation based ecological hydrology method, groundwater depth should be controlled during 3m~4.5m in study area.When water-soil-ecosystem is safety, the groundwater level can make the vegetation grow normally, soil salinization can be controlled, water-saving agriculture can be moderately developed and water resources is security;the numerical simulation of groundwater exploitation is established, the result shows that: annual exploitation quantity of groundwater 4×108m3is suitable, the average groundwater depth is 3.11 m.(2) Taking the largest groundwater exploitation quantity as objective function in typical area, the soil salinization prevention, groundwater level dynamic balance, salt and water balance as the constraint condition, the surface water and groundwater combined exploitation model is established, then the paper uses Modflow software to simulate different regulation of groundwater level, and puts forward development scheme set, after that, the different schemes are simulated by using salt balance model,the results show that: according to the comprehensive evaluation of underground water quality, crop root zone soil salinity, water quantity and operability, the underground water regulation level is about 2.5m~3m during crop growth period in typical area,the proper ratio of surface water and groundwater is 1.06~3.02;field drain salt with winter and spring irrigation, salt leaching ration is 2700m3/hm2, the winter irrigation is once every 2 years, spring irrigation is once every 5~10 years, farmland irrigation and drainage ratio should be 11.5%~11.9%.(3)Using trend extrapolation and water quota method to forecast water demand in planning level year,results show that:the total water demand is 13.894×108m3in 2015,13.164×108m3in 2020, 12.593×108m3in 2030; with the industrial structure adjustment and efficient water-saving agriculture development,agricultural water demand gradually decreased which accounts for the proportion of 83.36% in 2030, the proportion of industrial water demand increased gradually, reaches to 12.06% in 2030.(4) Choosing the minimum amount of water deficit and water supply cost as objective equation,Considered the minimum operation water level of Bosten Lake, double control index of groundwater and other reasons, the paper establishes water resources reasonable allocation model for multi-objective constraint. In the process of solving, cellular particle swarm algorithm is used to solve this model. Theresults show that: in different level years, water supply and demand balance can be achieved, the water level of Bosten Lake is all above 1045.0m; the agricultural irrigation scale should be better controlled about15.33×104hm2, in which the efficient water-saving irrigation area should be controlled about 62.7%~80.6% of total irrigation area, agricultural water diversion ratio(the ratio of surface water and groundwater water) should be controlled about 2.653~3.278.(5)Considering the characteristics of water resources in arid area and actual situation in Yanqi Basin,establishes water resources carrying capacity evaluation system,which covers 4 aspects(water resources system, social system, economic system and ecological system), 15 indicators, then uses the lattice theory to calculate evaluation index weight, and weighted ideal solutions method is used to evaluate WRCC for different level years, after that, puts forward water resource carrying index model to calculate the scale of economic-society development, the results show that: the population density, rural per capita living water,GDP growth rate, water consumption of industrial added value, irrigation water rate and forest coverage rate are main factors which affect WRCC; WRCC values are 0.4989 in 2011, 0.5307 in 2015, 0.5441 in2020 and 0.5459 in 2030, this value increased slowly and WRCC level changes from grade Ⅳ(in 2011)tograde III(in 2015,2020,2030); at the present level of economic-society conditions, the water resources can load 40.5 billion RMB for economic development in study area.