Studies On Models And Theories For Well Flow Due To Confined Water Exploitation

Groundwater exploitation has become nowadays one of the main factor that change the movement way of groundwater and also the main reason causes environmental and geologic hazard such as subsidence and sink of ground. Studies of the subject involved in this dissertation are important, because it provides a tool for knowing and mastering the information of groundwater change, and test methods of geohydraulic parameters. What's more, it plays important role in discovering some mechanism for subsidence, sink and fissure of ground and other environment geology disaster due to pumping groundwater.Based on the exsiting achievement about the models for well flow of groundwater and related theoretical solutions, and on account of some defect in the models and theory for groundwater exploitation, this dissertation has made some development and improvement for the models and theories of well flow due to confined water exploitation. The main original work and innovative achievements are as follows:1. To reduce the amplitude and affected area of drawdown of hydraulic head in confined aquifer caused by pumping, a new vertical well is designed, which contains double screens. With such a kind of well, a 3D flow model for confined aquifer, subjected to pumping and injection in synchronou or nonsynchronous way, is developed. Then, by application of Hankel transformation and Laplace transformation, the corresponding analytical solution is obtained, which is more general and can reduces to the solutions for full penetrating well and partial penetrating well in leaky confined aquifer and also to Theis's (1935) solution. The solution is used to analyze interplay of flow casused by pumping and injection and the change of hydraulic head in the confined.2. When pumping in the coastal leaky confined aquifer with runoff toward ocean, well flow may be influenced by not only the tide, but also the runoff. In order to study the comprehensive effect of groundwater flow under several factors, a mathematical model is formulated, and then by double Fourier transformation, the analytical solution is presented, which is consistent with some available solutions under a simpler condition. Based on the present solution, the effect of tide, runoff and other factors on well flow and hydraulic head in coastal confined aquifer is studied.3. Some pumping wells located above the confined aquifer without penetrating the covering layer of confined aquifer, and the water infiltrating from confined aquifer through the well bottom is continuously pumped off, which may lead to drawdown of hydraulic head in confined aquifer. For sucn a special problem, a mathematical model with three different lateral boundary conditions is developed for groundwater flow in the confined aquifer, and three ananlytical solutions are presented. The development and distribution of drawdown of hydraulic head under three lateral boundary conditons is compared. And the responses of hydraulic head under three lateral boundary conitions to different factors, such as leakage, anisotropy, the area of well bottom, thickness and width etc, are analyzed in detail.4. With consideration of radomly vertical distribution and antisotropicity of wellbore skin, and layered formation and antisotropicity of the the confined aquifer, two mathematical models for groundwater flow are developed. One model is neglected of skin storage and the other takes consideration of skin storage. And by finite diffence method, the semianalytical solutions for two models are obtained. The present solutions can reduce to some previous available solutions with simple skin conditions.The new solutions can be ued to analyze the effect of nonuniform and anisotropic wellbore skin on the drawdown and flow rate in layer-formulated and anisotropic confined aquifer and the different effects of negative and positive skin on drawdown and flow rate.