Impact Of Closing Self-prepare Wells On Groundwater Regime And Adaptive Strategies

Closing self-prepare wells is an inevitable option for conservation of groundwater and protection of hydrogeological environment. However, improper close would genereates new hydrogeological environmental problems and thus affects urban emergency water supply and economic and social sustainable development. Therefore, evaluating the effect of closing self-prepare wells and figuring out proper schemes is significant in both theoretical and practical aspects for guaranteeing urban water supply, conserving groundwater and promoting urban sustainable development.This paper using Baoji City in Shaanxi Province as a case study with theoretical analysis and analog computation integrated method analyzed the effect of closing self-prepare wells to shallow confined water regime and discussed proper schemes and adaptive strategies. The major conclusions are as follows:(1) Through analysis of annual and interannual shallow confined water regime in year 1990 to 2004, it was observed that shallow confined water level was obviously influenced by closing self-prepare wells when other recharge and discharge conditions didn't change much. Hydrograph of different observation wells all showed a break point at year 2000, which was water level decreased gradually before closing self-prepare wells and reached the peak at year 2000 with maximum depth of 27.55m to 89.10m and the it gradually recovered achieving maximum depth of 16.65m to 72.34m in year 2004. The minimum depth in some area was merely 3.88m. This indicated that change of groundwater exploitation caused by closing wells directly influenced variation of shallow confined water level. Interpolation results of geostatistics showed that the space distribution of shallow confined water level in city center was also affected by exploitation intensity.(2) A hydrogeology conceptual model and a mathematical model were built for Baoji City center. FEFLOW software integrated with GIS was employed to solve this model. In the parametric recognition process, the simulated curves were well coincide with practical curves, mean square root errors of water level for each well were within 10% amplitude and the correlation coefficients between simulated value and real value were over 0.95. In addition, the testing errors of this model were relatively small with high correlation coefficients. Results of recognition and tests demonstrated this built groundwater model was correct. The boundary conditions were generalized properly and the selection and partition of parameters were reasonable. It objectively depicted hydrogeology conditions in this area, and numerical simulation results were reliable that could provide a viable method for groundwater regulation.(3) Two regulation scenes were design in this paper. One was to achieve the objective of controlling groundwater level within 25m to 35m through closing self-prepare wells to reduce exploitation. The simulation results of groundwater level indicated that it was realizable to control groundwater level in 35m through scientific and orderly closing self-prepare wells and properly control groundwater exploitation and distribution, thereby achieving dual purpose of groundwater conservation and hydrogeological environment protection. Another scene was assuming this city would encounter sever drought in some year in future, and surface water couldn't satisfy urban water supply at all, so that groundwater was used as emergency water with emergency water wells opened to increase groundwater exploitation. In this situation, groundwater regime variation was simulated. The results showed when groundwater exploitation reached 62.93 million m~3, water level in exploitation points would dramatically decline 40 to 50m and generate a large-scale depression cone. Nevertheless, if measures of stopping or limiting groundwater exploitation were taken, in average year recharge and discharge situation, groundwater level in Baoji City center could recover to what before emergency exploitation in the next 1-2 years. This declared that if groundwater was actively conserved in wet years and average years, the emergency groundwater could be used in dry year.(4) Based on regulation requirements of Baoji City center, self-prepare wells were divided into exploitation self-prepare wells, emergency self-prepare wells and closing self-prepare wells. According to groundwater exploitation in different scenes in Chapter 5, the amount of exploitation and emergency self-prepare wells was calculated, and adaptive strategies for management of various kinds of self-prepare wells were proposed.