Drawdown Solutions with Variable Drainable Porosity

Abstract

Laboratory column studies are done to investigate the variation of drainable porosity in relation to water table depth. Corresponding functional relationships are developed between drainable porosity and water table depth. The Boussinesq equation for non‐steady‐state ground‐water flow is adapted and suitably modified by incorporating the variable drainable porosity function. The modified equation is solved using the extrapolated Crank‐Nicolson difference scheme for predicting water table depth in relation to space and time. A sand‐tank model experiment is done to find observed values of water table fluctuations. The prediction from the modified Boussinesq equation is compared with observed data. It is discovered that incorporating variable drainable porosity in the computation increases the accuracy of the prediction at all distances from the drain compared with using a constant value for drainable porosity. It is also discovered that water table predictions from the modified Boussinesq equation varied with observed data. This is attributed to lag time between the initiation of the drain outflow and response in water table drawdown in mathematical computation.