Gravity drainage of a sand profile under a time-dependent surface flux

Abstract

The replenishment of groundwater supplies from recharge trenches often involves the use of water containing quantities of suspended solids which eventually become deposited on the sides and bottom of the trench with a consequent decrease in intake rate. This process is simulated numerically in one dimension by using a finite difference solution of the flow equation with a time-dependent surface flux boundary condition. Three algebraic functions are used to represent the flux change so that different physical characteristics of the system can be studied. The numerical results indicate that for a reasonably slow rate of flux reduction water content and pressure head profiles of a steady state configuration, appropriate to the flux at that time, are obtained. However, with a more rapid flux change unsteady state conditions remain established through the profile and predictions of water content and pressure head can only be made using an unsteady state analysis.