Optimum Allocation Of Water Resources Based On Ecological Health In Arid Oasis Area

The middle reaches of the Heihe River are located in the inland arid area of the northwest,and the water resources are seriously scarce.The sustainable development of the area is highly dependent on and sensitive to water resouces.In recent years,with the increasingly prominent contradiction between water supply and demand,agricultural water seriously squeeze the ecological water,leading to the growth of social and economic benefits and heavy ecological environment costs born.The research on water resources optimal allocation based on ecological health is of great theoretical and practical significance to promote the sustainable utilization of water resources and improve the fragile ecological environment in the middle reaches of the Heihe River.Based on the analysis of the evolution of ecosystem and the driving factors in the middle reaches of the Heihe River,this paper established an index system to measure the ecological health of oasis.Based on the principle of water and energy balance,and sandstorm dynamics,the appropriate oasis scale,ecological scale and cultivated land scale were determined.The available water resources in the study area were calculated for different hydrological years,and vegetation and wetland was calculated by using the method of diving evaporation and water evaporation,while the water demand of the living conditions,industry and agriculture were calculated by the quota method.Considering the uncertainty of upstream water,precipitation,evaporation,crop yield and price,based on the hierarchical analysis of large-scale system,a multi-objective interval two-layer optimized water distribution model based on ecological health was established.Based on MATLAB programming,the optimal allocation of water resources between counties,departments and crops in different planning years and different hydrological years was obtained.The main conclusions are as follows:(1)Based on the anomalous percentage of runoff,five kinds hydrological years was divided,especially high flow year,high flow year,normal flow year,low flow year,and especially low flow year,respectively.According to the " Water Distribution Scheme of Heihe River Mainstream ",the available water resources in five kinds hydrological years are [14.65,15.68],[14.77,15.25],[14.38,15.33],[14.40,14.70],[13.77,14.25] ×108 m3,respectively,of which groundwater allowed to use was 4.81×108 m3.(2)Based on the land use map of 1986,2000 and 2011 in the middle reaches of Heihe River,the evolution trends and reasons of forest land,grassland and wetland area were analyzed.The results showed that the area of forest land and grassland decreased from 1986 to 2011,while the wetland area decreased first and then increased.The main reasons for these changes were that the cultivated area occupied the ecological area,the production water squeezed ecological water use,the implementation of water engineering construction and wetland restoration measures,etc.(3)Considering the influence-factors of oasis ecosystem,the index system of oasis ecological health was determined,including suitable oasis scale,suitable cultivated land area,suitable ecological scale,suitable ecological groundwater level and minimum ecological water requirement protection.Based on the principle of water and energy balance,and sandstorm dynamics,the appropriate oasis scale,ecological scale and cultivated land scale were determined.In the critical steady state,of five kinds hydrological years,especially high flow year,high flow year,normal flow year,low flow year,and especially low flow year,the interval of appropriate oasis scale is [346.8,496.6],[356.4,473.3],[340.0,469.0],[349.0,425.1],[336.1,429.1]×103 hm2,respectively,and the interval of suitable cultivated land area is [131.2,140.4],[132.3,136.6],[128.8,137.3],[129.0,131.6],[123.3,127.6] ×103 hm2,respectively;The effective vegetation coverage in the study area is 22%~28%,and the critical vegetation coverage is 47%.In the middle reaches of the Heihe River basin in 2013,the actual oasis scale and cultivated land area exceeded the suitable range,and the ecological protection area did not reach the effective vegetation coverage.(4)Based on the phreatic evaporation method and water evaporation formula,the water demand of vegetation and wetland were calculated,while the water demand of the living conditions,industry and agriculture were calculated by the quota method.In the middle reaches of the Heihe River basin in 2013,the total water requirement was [17.02,21.13] ×108 m3,of which living,industrial,agricultural and ecological water requirement were 0.46,0.31,[12.95,15.23],[3.30,5.13] ×108 m3,respectively,with [1.92,6.03] ×108 m3 water shortage.In 2020,the total water requirement would be [16.30,22.10] ×108 m3,of which living,industrial,agricultural and ecological water requirement were 0.57,0.28,[11.42,14.57],[3.86,6.55] ×108 m3,respectively.In 2030,the total water requirement would be [16.58,22.40] ×108 m3,of which living,industrial,agricultural and ecological water requirement were 0.67,1.01,[10.53,13.43],[4.46,7.41] ×108 m3,respectively.(5)Under the for principles of ecosystem health,safety,efficiency and equity,based on the hierarchical analysis of large-scale system,considering the uncertainty of upstream water,precipitation,evaporation,crop yield and price,a multi-objective interval non-liner two-layer optimized water distribution model was established.In the model,the largest economic benefits and the minimum square sum of water deficit were regarded as the objective functions.Based on MATLAB programming,the optimal allocation of water resources between counties,departments and crops in different planning years and five kinds hydrological years was obtained.After the optimization in 2013,the economic benefits are [96.53,113.72] ×108 yuan,and the optimized economic benefits were slightly decreased due to ensure the ecological health water.The optimized agricultural water accounted for 73%~74% of the total water use,and the ecological water accounted for 21%~22%.In 2020,the optimized economic benefits would be [158.42,181.77] ×108 yuan.The optimized water for Ganzhou,Linze,Gaotai accounted for 45%~48%,25%~26%,27%~29% of the total available water;Ecological water accounted for 25%~28%,while Agricultural water accounted for 64%~68%.In 2030,the optimized economic benefits would be [338.08,361.82] ×108 yuan.The optimized water for Ganzhou,Linze,Gaotai accounted for 46%~49%,24%~25%,26%~30% of the total available water;Ecological water accounted for 28%~32%,while Agricultural water accounted for 56%~61%.The water resources optimal allocation results between crops were similar in current year and planning years.In order to ensure the minimum grain requirements,wheat,field maize and other grain crops are small in water shortage,while Seed maize's water requirement couldn't meet due to the large planting area.