Study On Unsteable Pumping Model Of Confined Boundary Aquifer Under Non-Darcian Effect

The study of seepage mechanism models related to groundwater exploitation has always been a hot spot in the hydrogeological field.At present,most studies on pumping-induced flow in confined boundary aquifers are discussed under the background that seepage satisfies Darcy's law.The problem of pumping-induced flow with non-Darcian effect in the confined boundary aquifer has not been reported yet.Therefore,considering the non-Darcian effect,this paper proposes a mathematical model of transient pumping-induced flow in a confined infinite aquifer based on the Izbash equation,and uses Boltzmann transform to derivate a simplified analytical solution.By imaging-well system with superposition principles,analytical solution for drawdown-time behaviors in aquifers with semi-infinite recharge,semi-infinite barrier,and right-angle boundary are also developed,and using COMSOL Multiphysics to build numerical models to verify those analytical models above.The influences of hydraulic parameters,boundary effects and well storage effects on water level drop are analyzed,and the characters of transient flow movement near the confined boundary aquifer are investigated.The main conclusions of this paper are as follows:(1)The two coefficients in the Izbash formula have the same response to the aquifer drawdown In the early stage of pumping,as the quasi-hydraulic conductivity coefficient K_I and the non-Darcian coefficient n increase,the water level drop in the aquifer also increases.In the later stage of pumping,the greater K_I and n result in the greater drawdown.(2)numerical solutions,based on Izbash equation and Forchheimer equation,of the drawdown of the non-Darcian pumping-induced flow in an infinite confined aquifer are developed by using the software entitled COMSOL Multiphysics,respectively.By compared with the results of case studies from analytical solutions,it is indicated that,under any boundary condition,there is a difference between the analytical solution and the numerical solution.The error is controlled within 15%.(3)Compared with the drawdown-time curve under an infinite aquifer,according to different boundary attributes,different boundary combination effects have different effects on drawdown.(4)The impact of well storage effect on aquifer drawdown is mainly occurred in the early pumping time.In addition,the larger the non-Darcian coefficient n can lead the shorter the hysteresis of drawdown due to well storage effect.(5)Through the parameter sensitivity analysis of the non-Darcian coefficient n,the quasi-hydraulic conductivity coefficient K_I,and the water storage coefficient S,with and without considering the wellbore storage effect,the drawdown in the aquifer has the greatest effect on the Non-Darcian coefficient n Sensitive,the least sensitive to the water storage coefficient S.