Combined Utilization Research Of Surface Water And Groundwater In Oasis Irrigation District Of Southern Margin Of Tarim Basin

How to achieve optimal allocation and efficient use of oasis water resources has always been a key scientific issue in oasis science.More than 90%of the current Xinjiang oasis is used in agricultural irrigation districts.The optimal allocation of oasis water resources is largely reflected in the optimal utilization of water resources in irrigation districts.In the past few decades,due to population growth and economic development pressure,the area of Oasis agricultural irrigation district has continued to expand.The amount of surface water and groundwater resources used in the Oasis Irrigation District is also increasing.How to rationally realize the optimal utilization of water resources in Oasis irrigation area is the key and difficult point of Oasis water resources management.In the mountain-oasis-desert ecosystem,water resources are derived from the surface runoff of melting ice and snow in mountainous areas and are dissipated in oasis agricultural irrigation and desert.When the surface runoff cannot meet the water demand in the irrigation area,groundwater becomes an important supplement.Therefore,the core point of the optimal utilization of water resources in the oasis irrigation area is the joint utilization of groundwater and surface water.This is especially the case in the current expansion of the oasis area,changes in planting structures,and increasingly stringent water constraints(especially groundwater).How to realize the optimal utilization of surface water-groundwater is a key scientific problem facing Xinjiang,especially the southern Xinjiang oasis,and a realistic problem that needs to be solved locally.This paper selects the oasis in the southern margin of the Tarim Basin,which is characterized by poor social economy and oasis water resources management.As an important distribution area of Xinjiang oasis,in the past 30 years,its oasisization process has intensified and the farmland area has been increasing.In the past 10 years,due to the good light and heat resources in southern Xinjiang,the agricultural planting structure in the region has been transformed from traditional wheat,cotton and corn to economic forest fruit.The expansion of farmland area and the change of planting structure have made optimal use of water resources.An urgent need is put forward.Based on the Cele National Field Observation and Research Station located in the central Hetian area of the southern margin of the Tarim Basin,the Cele Oasis is selected as a typical research area.Firstly,the change of the oasis landscape pattern in the past few decades of Cele Oasis is analyzed.Identify the current planting structure,area and layout of the Cele Oasis.Combined with the countermeasures and monitoring analysis of the water consumption characteristics of red jujube and walnut in the main economic crops of Cele Oasis,the water demand of the oasis under the existing planting structure was clarified.Secondly,based on the characteristics of the long-term runoff of the Cele River,the safety threshold of the groundwater resources of the Cele Oasis is analyzed.On the basis of establishing a hydrological model to simulate the groundwater safety threshold,the maximum amount of groundwater exploitation available for the groundwater resources of the Cele Oasis under multiple scenarios is determined.Thirdly,the optimization of water resources in the irrigation area is transformed into the optimal allocation simulation of the groundwater resources that can be mined in Cele Oasis.Irrigation water wells are used to mine groundwater to irrigate farmland irrigation areas.By analyzing the number and distribution characteristics of the existing wells in Cele Oasis,the objective equation with the lowest mining cost is established,and the optimization model is constructed and the optimal well location quantity and spatial layout based on the status quo are analyzed.Finally,the optimal allocation study of surface water and groundwater combined utilization is established.Through different irrigation modes,an optimal allocation model is established to analyze the combined water distribution schemes of surface water and groundwater under different scenarios,and the schemes and suggestions for joint utilization of water resources under different scenarios are proposed.The main conclusions obtained from the study are as follows:(1)During the period of 1970-1990,1990-2000 and 2000-2013,the area of the Cele Oasis irrigation area changed significantly,with annual change rates of-0.3%,1.6%and 3.7%,respectively.The area of agricultural land in 2013 increased from 91.10km2in 1970 to 162.66 km2.Compared to 1970,the proportion of farmland in 2013 increased by 78.5%(compared to the 1970 data).The expansion of irrigation districts greatly affected the stability and ecological sustainability of the oasis landscape.(2)At present,the jujube,walnut and pomegranate planting area of Cele Oasis account for 59.4%,23%and 5.7%of the total oasis farmland,respectively.The proportion of irrigation water to total water consumption is 68%,17.7%and 5.8%,respectively.Crops accounted for 88.1%of the total area of the Cele Oasis,and its water consumption accounted for 91.5%of the total water resources.This result shows that the planting structure of the Cele Oasis has undergone great changes,and the food crops that have been turned into economic crops have been basically converted from decades ago.Red dates have become the largest economic crop in the Cele Oasis.The water consumption experiment was carried out on jujube and walnut.The results showed that the transpiration water consumption of jujube was about 342.7m~3/mu,among which the transpiration water consumption in the main growth period accounted for more than 58%of the total growth season;and the transpiration water consumption of walnut was about It is 87.23 m~3/mu,in which the transpiration water consumption during the main growth period accounts for more than 60%of the total growth season.(3)The Cele Oasis allows groundwater extraction to be approximately 0.9242×10~8 m~3/a.The exploitable amount of groundwater is calculated by the mining coefficient method.The comprehensive extraction values of the water supply according to different years(the years of abundant water,the year of flat water,and the year of dry water)are1.2,0.7,and 0.55,respectively.The groundwater recoverable amount is 1.2015.×10~8m~3/a,0.647×10~8 m~3/a,0.5083×10~8 m~3/a.At present,the groundwater exploitation in the Cele Oasis irrigation area is about 0.6×10~8 m~3/a.Therefore,the exploitation of groundwater resources in the Cele Oasis tends to be saturated.(4)In the spatial optimization process of the 244 wells distributed in the current oasis irrigation area,after the maximum irrigation radius of each irrigation well is set to 1500 m,the optimization results show that the number of Cele Oasis wells has decreased by nearly three-quarters,and The minimum pumping irrigation cost was obtained after considering various costs.After re-optimizing the pumping rate of the well,the pumping rate of the well was reduced by 87m~3/h,from 217 m~3/h to 130 m~3/h.At the same time,the theoretical pumping rate was reduced from an average of 209m~3/h to an actual pumping rate of 170 m~3/h,and the average pumping rate of all wells was reduced by 39.02 m~3/h.It provides a method for optimizing the layout of groundwater irrigation wells in arid areas,which can provide management advice to local governments.In addition,it can effectively guide the development and utilization of groundwater by local residents,and at the same time,it plays an important guiding role in the sustainable development and utilization of groundwater.(5)In the study of the combined use of surface water and groundwater,the current irrigation districts are grouped.In the case of considering the use of only surface water,the round irrigation groups in June,July and August are all 5 groups,but due to the water diversion period of each branch channel.Both are relatively long,and the time difference value is relatively large.Therefore,the total water diversion time in June,July and August is relatively long,and the difference in the continuous water diversion time of each wheel irrigation group is also relatively large.According to the analysis of the water resources of Cele Oasis for many years,it can continue to increase the cultivation of 33.51km~2 red dates and 20.82 km~2 walnuts.It is recommended to expand to the east and west of the Cele Oasis.