Study On The Dynamic Change And Simulation Of Deep Groundwater In Dezhou City

This paper is accomplished on the basis of Natural Science Foundation of Shandong Province of China under project, the research on freshwater salinization evolution under exploitation conditions in alluvial plain of the Low Yellow River. In view of this major environmental geology problem in Dezhou City that the rapidly-expansion of groundwater drop funnel has been caused by continuous overexploiting of deep groundwater in recent years, the dynamic change of deep groundwater in Dezhou City was systematically analyzed as well as the evolution and development of hydrodynamic field and deep drawdown cone in temporal and spatial variation was simulated by the application of the Visual MODFLOW Model. The exploitation project was proposed that the drawdown cone would not further expand. The study findings can provide a scientific basis for rational development and utilization of deep groundwater resources and controlling land subsidence in Dezhou City.The environmental geology and hydrogeological conditions in Dezhou City were analyzed as well as exploitation and utilization situation of deep groundwater, the dynamic variation of the groundwater level and distribution characteristics of the depression cone. The extended discipline of depression cones of deep groundwater was discussed. Under the exploitation situation, the elevation of central water level of groundwater drop funnel in this region was -108.00m, the elevation of boundary water level was -50.00m. The equivalent water level was expending at the average velocity of 344.40m/a. The elevation of central water level of groundwater drop funnel was deepening at the average velocity of 3.16m/a in vertical dimension. The drop funnel was gradually expending in horizontal and vertical dimension with continuous and excessive exploitation of deep groundwater.On the basis of hydrogeological conditions generalized in this region, Visual MODFLOW software was applied to build mathematical model of groundwater and stimulate the seepage field of groundwater. It predicted the expansion of groundwater drop funnel and the change of underground water level under the conditions of exploitation situation and different designed exploiting volume by the model built. The depth reduction and variation of groundwater under different design schemes for pumping rate were argued by contrast analysis of the calculated results.The forecasting result under the current situation of groundwater exploitation indicated that the drawdown of water level would increase more with the continuous exploitation when the exploiting volume of current situation was 2047×10~4m~3/a. When t (time) was equal to 5a (2011), s (the decline depth of groundwater) was at 4.81-22.65m and the annual deceleration was at 0.96-4.53m/a. When t was equal to 10a(2016), s was at 14.32-32.87m as well as the annual deceleration was at 1.43-3.29m/a, and then the average elevation of central water level of funnel was -118.06m. The forecasting results under different design schemes for exploiting volume showed that the groundwater level would continuously decrease if the present exploiting quantity was still kept at 2047×10~4m~3/a, which the depth of central groundwater level of funnel was 144.95m in 2010. While exploiting quantity cut down to 1950×104m~3/a, the groundwater level still constantly decreased, which the depth of central groundwater level of funnel was 133.90m in 2010. Only when exploiting quantity further cut down to 1750×104m~3/a, the groundwater level would never descend after 2009, and then it would begin ascending, which the depth of central groundwater level of funnel was 120.25m in 2010.According to the model stimulation of groundwater flow and the results of water balance analysis, the allowable exploiting volume of III aquifers in this region is 1750×10~4m~3/a. The key measure to protect deep groundwater resources in this region is scientific planning of underground water, adjusting exploiting volume of underground water, and ensuring that exploiting quantity do not surpass supply quantity in order that it can reach a benign circle with the balance of exploitation and supplementation.