Groundwater Hydrological Process And Sulfate Formation Mechanism In Kashi Economic Development Region, Xin Jiang, China

iiiKashi is China’s improtant western open port which also is the political, economic and cultural center of Kashi region. Along with the development of the city, the demand of water for industrial production and citizens is increasing which has become an impotrant issue of local water resources development and utilization in the futrue. However, Kashi and its surrounding counties belong to water shortage area which salinity, total hardness and sulfate content in the groundwater seriously overweight varying degress. Actively improve the conditions of urban production and living water has become an improtant strategy to local imminent. Based on “Groundwater evolution and ecological effects in Kashi Economic Development Region, Xin Jiang, China”, this resreach comprehensive studied the groundwater hydrological process and renewable ability of groundwater and sulfate in the source and formation of groundwater chemical conditions and hydrodynamic donditions based on the theory of groundwater dynamics and hydrogeochemical through the environment isotope, groundwater flow numerical simulation and multicomponent reactive solute transport modeling methods in order to provide scientific theoretical to promote reasonalbe development and utilization of local water resources. The main recognitions and achievements are as follows:1. Based on the study of geological, geomorphological,geologicalstructurehydrodynamic field and environmental isotope,the hydrological processes in the study area can be divided into three types:hydrological processesof large scale and small scale with simple basementstructure, hydrological processes ofmoderate scale with basement relief.2. The characteric of groundwater hydrologic process in Kezile River basin which located in the north of study area seems as the hydrological processes of large scale and with simple basement structure, it shows that groundwater have it’s sources from the southwest tianshan mountains, and supplied by theriver valley undercurrent,ice and snow melt water and rainfall infiltration.Then groundwater recharged by surface water from mountain exitto kyzyldiluvial sector,while flow through alluvial plain with water fine soilbearing medium, groundwater depth becomes shallow, local area exposed in the form of springs,and supply surface water.The aquifer can be divided into two groundwater flow systems:the local water flow systemwith the depth of of 150 ~ 200 m, groundwater flow rate is 1.0 ~ 1.5 m/d andits age less than 50 years; the regional water flow systemwith depth more than 200 m,groundwater flow rate is less than 1.0 m/d and age greater than 7 ka.Groundwater renewal rate reduced gradually from 7% to less than 1%from piedmont pluvial fan to the alluvial plain.3. The hydrological processesof groundwater on the southernof study areanamed Gaiziriver basinseem as the medium scalewith basement relief. Groundwater from the kunlun mountains area,and receive recharge from precipitationin mountainous area and bedrock fissurewater, then flow along the Gaizi riverrushed into diluvial sector, while groundwater come acrossthe Kumu Tage anticlineit becomes blockedand the direction of flow turn to east.Frequently conversion exist between river and groundwater rommountain exitto fine soil plain. Influenced by Gaizi river bridge anticline, there is a drop between two sides of anticline. Because of the formation fold, large thickness of unconfined aquiferformed in Gaizidiluvial fan.The aquifer can be divided into three groundwater flow systems: local water flow system with depth of 50 ~ 75 m, groundwater flow rate is 1.5 ~ 3.0 m/d, and age less than 20 years; Middle water systemwith depth120 ~ 160 m, groundwater age is less than 500 a,andflow rate is 0.5 ~ 1.5 m/d; the regional water flow system more than 250 m, groundwater flow rate is less than 0.5 m/d, and age greater than 10 ka. Groundwater renewal rate decreasedgradually from 7% to less than 2% from piedmont pluvial fan to the alluvial plain.4. Groundwater in Kushan River basin belonged to the small scale of simple basal structure groundwater hydrologic process which flowed from the diluvial fan to the fine soil plain in the east. In the front of blunt pluvial fan, surface water infiltration to the groundwater; To the alluvial fine soil plain, groundwater overflowed and recharged to surface water. Groundwater originated from the kunlun mountains area, with the influence the terrain and the hydrogeological conditions flowed to the eastern lowland plains. From Kushan River of the mountain pass, groundwater was recharged by the upstream groundwater, rain infiltration and the infiltration of the channel, along to the blunt pluvial fan, groundwater system developped three water systems: the depth of the development of the local water system was 75~100 m, groundwater flow rate was 1.0~3.0 m/d and groundwater age was less than 20 years; The depth of the development of the middle water system was 130 ~150 m, groundwater flow rate was 0.5~1.0 m/d and groundwater age was less than 5 ka; The depth of the development of the regional water system was more than 200 m, groundwater flow rate was less than 0.5 m/d and groundwater age was greater than 5 ka. From piedmont pluvial fan to the alluvial plain of fine soil, the groundwater renewal rate gradually decreased from 7% to 2%.5. Three kinds of different scal groundwater hydrologic process had obvious differences due to the different level drainage datum, terrain factors, geologicla structure and the aquifer permeability. In the north of Kezile River basin, the overall trend of groundwater was mainly controlled by the Tuman River which was the main drainage datum. The aquifer permeability, terrain slope of basement and groundwater flow speed were both gradually decreased. As the final discharge point in Gazi River basin, the spring and Gazi River controlled the groundwater flowed to the northe area and turned to the east with the block water effect of anticline structure. The existence of anticline structure influenced the groundwater hydrological process and covered up the changes of groundwater flow which caused by the basement terrain slope; In the south of Kushan River basin, the lithology of aquifer was mainly large thickness of sand gravel containing eggs and the basement terrain slope was bigger. The groundwater hydrological process was mainly effected by the aquifer medium and terrain.6. SO42- concentration distribution of groundwater was greater in the north and lower in the south which was gradually increased anlong the groundwater flow and presented significantly horizontal zoning characteristics. An obvious vertical zoning characteristic was showed by the tend of decrease of SO42- concentration with the increase of depthe in aquifer. The sulfate chemical characteristics of groundwater was influneced by the depth of grounwater, groundwater dynamic conditions, cumulative effect along the flow path and the sulfate hydrogeochemical action of gypsum mineral.7. Through the establishment of multocomponent reactive solute transport model, the hrydrogeochemical process of high sulfate formation drivened by the flow was revealed across the Kezile River section. The aquifer medium grain bulky with a penetration ability and the groundwater flowed fast, the leached functino of gypsum, calcite and dolomite was given priority to the recharge area of groundwater; While in the discharge area of groundwater, the water chemistry was given priority to the evaporation concentration and cation adsorption alternately due to the small aquifer medium particles and poor penetration ability.