Research On Groundwater Circulation And Environment Effect Of Dusitu River In Ordos Basin

Ordos basin is a large scale groundwater basin overlapping Shaanxi, Gansu, Ningxia and Inner Mongolia provinces or autonomous regions. Dusitu river is located in the northwestern of Ordos basin and belongs to Etuoke Qi of Inner Mongolia autonomous regions. Although the groundwater system had been researched by previous researchers from some local regions or a certain side, but groundwater circulation and environment effect influenced by groundwater utilization haven't been researched from the point of the basin. The latest date of groundwater flow field and hydrochemistry field is obtained in study area,using Various methods including hydrogeology investigation, hydrogeological drilling and pump test, Packer depth sampling, hydrochemistry and isotope. On the basis of the groundwater dynamics, hydrochemistry and isotopic features of groundwater, groundwater circulation depth and circulation patterns of the different patterns have been defined to groundwater system in Dusitu river. Circulation law of different deep groundwater have been studied by means of hydrochemistry distribution feature of shallow and middle groundwater and the change of the ratio of molar concentration along the groundwater passes. Environment effect influenced by groundwater utilization have been studied and the protecting measures of groundwater resources have also been suggested.The groundwater aquifer system in Dusitu river can be divided into Wind-drift and alluvial-laustrine pore aquifer system in Quaternary sand and clastic pore-fissure groundwater aquifer system in Cretaceous rocks, which is dominant for aquifer system in Dusitu river, including Luohandong, Huanhe, Luohe water-bearing layers aquifer system. Precipitation infiltration recharge is the main resource to recharge groundwater. And groundwater is discharged by phreatic evaporation, overland flow, artificial exploitation, lateral runoff, while groundwater is discharged dominantly by phreatic evaporation. The dynamic types of groundwater can be divided into three types including infiltration- evaporation, infiltration-runoff, infiltration - exploitation -runoff.According to hydrochemistry and isotopic data obtained by Packer depth sampling and jigging pump test, the hydrochemical and isotopic features of groundwater has been studied as well as dynamics features of groundwater in Dusitu river. The depth of 200 to 250 meters is the boundary belt between the shallow circulation pattern and middle circulation pattern. The depth of 600 meters is the boundary line between the middle circulation pattern and deep circulation pattern. The shallow circulation pattern is characterized by fast circulation, high renewal capability and the groundwater age of less than 50a. Middle circulation pattern is characterized by relatively fast circulation, relatively abundant water resources the groundwater age of less than 5000a, and 5000 to 20000 a in local scope. Deep pattern is characterized by low flow velocity, large circulation depth of 1000m and groundwater age of 13000 to 15000a, less than 13000a in ground watersheds.The shallow and middle groundwater are characterized by by fast circulation from horizontal zonal characteristic of hydrochemistry, and the chemical fields of local groundwater is horizontal zonation obviously. The east and north of study area is seepage zonation of groundwater with high topography, deep groundwater depth, large percolation gradient, fast circulation and less water-rock interaction. While the groundwater moves to the lower reaches, total dissolved solids of groundwater is more, the soluble salt content of groundwater increases obviously and the hydrochemical type is mainly SO`Cl with high mineralization for the discharge area west to Bulongmiao. On the basis of hydrochemical and isotopic features of shallow and middle groundwater and the change of the ratio of molar concentration along the groundwater passes, shallow and middle groundwater moves towards Dusitu river. Middle groundwater have gone through more complicated evolution course and stronger water-rock interaction than shallow groundwater.On the basis of analysis of current situation for ecological environment with vegetations types, suitable groundwater depth for vegetations, distribution features of vegetations and groundwater depth condition, current situation vulnerability of ecological environment can be divided into four types, that is, relative fail area, mild fail area, medium fail area and serious fail area. The groundwater flow field forecasted will not change too greatly after 20 years, and the groundwater depression forecasted will not obvious in study area, if adapted Optimum exploitation scheme. The influence to ecological environment is not obvious, which is caused by groundwater exploitation for Sanbeiyangchang, Chahantaige and Gashatu well fields. And after Baolehaoxiao, Bayanbulage and Haolebaoleji well fields having been exploited, groundwater depth increase less and the interaction between them is small. As the ecological environment is fragile, the protecting measures of groundwater resources should be taken. while groundwater is exploited, if adapted optimum exploitation scheme, the protecting measures of well fields should be taken.