Evolution Prediction Of Ground Water Environment In Shigatse City And Investigation Of The Protection Measures

This dissertation is based on the proposed Shigatse city Northern Suburbs Waterworks in Tibet. The hydro-geological model were established which on the basis of the detailed field survey in water source, and collection for hydrogeology data. We predicted influence area and drawdown, which based on long-term extraction of groundwater, by use of MODFLOW in finite difference method and mathematical analytic method. Meanwhile, water supply capacities of water source were demonstrated; the impacts of long-term water extraction on ecological environment were analyzed. Finally, this dissertation puts forward some protective suggestions, which could be used for environment protection and water-supply safety of water taking in plateau area.According to the pumping tests data, Water Environmental Quality and Water Quality Hygiene were evaluated. The groundwater quality grade was determined as good and conforming Sanitary Standard for Drinking Water Quality (GB5749-2006), which can be used as a source of drinking water.Natural replenishment parameter of Ground Water was calculated to be77896.93m3/d by use of pumping tests data, which satisfy the mining plan of waterworks (50000m3/d). At the same time, groundwater hydro-geological model was established by use of MODFLOW in finite difference method. Based on this model, we predicted influence area and drawdown with long-term extraction of groundwater. The results of prediction by mathematical analytic method showed that the biggest water level drawdown is24.55m (ZK7), and the radius of influence would be1479.80m. Meanwhile, the results also showed that southern and western area of water source has the most influence with long-term water extraction and it’s followed by eastern and northern area in the effects.According to the results of predicting, the impacts of long-term water extraction on ecological environment were analyzed. The analysis showed that it has little influence on quality of water source if the disaster land subside quantity up to0.078m during20years operation period. Hereby, based on the actual situation in water source, the Wellhead Protection Zone was confirmed as follows:the region within borders of125m radial distance based on well centered was supposed to be the top protected region. The region north to Yarlung Zangbo River, within borders of1250m radial distance based on top protected region was confirmed as secondary protected region.Based on the groundwater environment present condition evaluation result, evolution trend of groundwater surroundings feature and reserve grading, some pertinent’suggestions were proposed to realize safe water supply as practical as possible.