Evaluation And Rational Exploitation Study For Groundwater Resources Of The West Plain In Yili Valley

The study area is a bridgehead of the “Silk Road Economic Belt” in China facing other countries of the Central Asia which located in the northwest of China.Its demand on water resource is gradually increasing with the opening to the west and development of industrial parks.The wide distribution and convenient for utilization of the groundwater is one of the important guarantee of water resource.It is of important practical significance to research reasonable exploitation of groundwater resource and protection of ecological environment,But the exploition of the groundwater resource lacks scientific planning due to previous shallow research level on the hydrogeology.Therefore,this paper depending on the project of Survey on 1:50000 Hydrogeology of the West Plain in Yili Valley undertaken by Xi'an Geological Survey Center of China Geological Survey,based on abundant field hydrogeology surveys,tests,and hydrogeological condition analysis,taking groundwater system theory as guidance to calculate hydrogeology parameters.Compute quantities of groundwater resource using the water balance method;and preliminarily explores the development and utilization of groundwater resource in the plain combined with the numerical simulation method.The following understandings and achievements are mainly obtained through research:1.The pore aquifer is the main aquifer in the study area and it possesses large thickness,coarse particle,strong storage and water supply abilities,good permeability and hydraulic conductivity,and large development and utilization space.After underground water is supplemented by surface water,it will flow to the lowest base level of erosion-Yili River in the plain from the front of north-south mountain,and hydrological cycle process of two to three times is generated due to dual function of landform and sediment during the flow process;and it flow from the east to the west in the east-west direction;finally,it outflows from China.2.Hydrogeology parameter partition of the research area preliminarily given through tests and field hydrogeology surveys.With water balance method,the supplement volumeof groundwater natural resource in the plain terrain is 1.93 billion m3 and output is 1.987 billion m3.It is presents slightly negative balance,and consistent with dynamic performance of groundwater water level.The groundwater resource volumes respectively are 2.0584 billion m3 and 1.8969 m3 when rainfall guarantee rate is 50% and 75%,which can be taken as the upper and lower limits of groundwater resource volume in the plain.3.There are many supplement sources of groundwater in the research area.The largest supplement source is river infiltration supplement,accounts for 33.6% of total supplement volume of groundwater,add the groundwater inflow from boundary account for 49.2% of the recharge.The next one is canal system irrigation,accounts for 22.3% of supplement,For further analysis,the supplement volume(canal system and field)through human impact accounts for 33.6% of total supplement volume,hence,it indicates that the influence of human factors on groundwater supplement volume is in a subordinate position;the groundwater will mainly discharge into the Yili River in the form of runoff or depression spring;finally,it outflows from China and into the Balkhash Lake.amounts to the total drainage amount of 53%.Phreatic water evapotranspiration and spillage of spring water is on drainage amount of 32%.The exploitation plan can be designed properly in the research area to lower the groundwater level in the high water-level and reduce evaporation from phreatic water,so as to improve the saline-alkali soil around the Yili River.4.Generalized hydro-geologic model is a 3D three-layer unsteady flow model.The north-south border is generalized because the fault zone is mostly the colline zone that consists of the mesozoic bedrock in front of the mountain of the research area,which plays a role preventing alpine fissure water and spring water from direct supply to the underground water in the plain.Riverbed subsurface flow from the bedrock fissure water is supplied to the groundwater in the plain by a mean that the north and south rivers flow through the low mountains and hills.Therefore,this part is generalized to be the second boundary.The east of Yamadu is the supply boundary,away from 60 km of the departure gate in the west of Yili River is drainage boundary.Overall upper boundary is the phreatic surface,but the bottom boundary is an impervious boundary because mudstone,sandstoneand its interbed from Neogene in underlying bed of the quaternary pore water-bearing layer and part of Jurassic stratum are aquitard.Based on the groundwater system generalization,the groundwater flow mathematical model was established.Using Modflow software to solve the groundwater flow mathematical model,and has carried on the identification and verification.By adjusting the parameters of the partition,in terms of the groundwater flow field,groundwater balance and hydrogeological parameters and the measured data is consistent,to ensure the reliability of the model.5.With the development trend of the water resource demand nearly 15 years in the research area as well as the relevant plans,the demand for underground water in short-term planning year(2020)and long-term planning year(2030)are respectively calculated under the different assurance rates,of which the annual demands for the underground water are223 million m3 and 242 million m3 under the assurance rates of 50% and 75% in 2020 and the annual demands for the underground water are 435 million m3 and 472 million m3 under the assurance rates of 50% and 75% in 2030.The calculated amount is less than the allowable withdrawal,so it can be assured in theory.6.The exploitation plan for underground water is designed based on the forecasting demands in the plain,that is,the water demands for the development of the urban planning and for industry & agriculture shall be taken into full consideration on the basis of existing withdrawal,and the underground water nearby the urban planning area shall be exploited in the traditional well-group exploiting mode.According to the plan,the affected radius is about 2-5 km,it means the exploitation amount meets the actual demand and does not produce the negative effect of the ecological environment.