Effect of Soil Moisture Hysteresis on the Water Table Profile Around a Gravity Well

Abstract

Gravity wells, pumped intermittently, can have different degrees of drainage in the unsaturated zone at the onset of water table recovery. Each part of the aquifer profile follows a specific scanning curve of rewetting. The measured hysteresis phenomenon of Oso Flaco fine sand and the hydraulic conductivity as a function of moisture content are incorporated in the finite difference form of the partial differential equations for steady and unsteady radial flow to solve for the soil moisture pressure distribution of one water table drawdown and three different kinds of recovery. The method of independent domains describes the hysteresis phenomenon and accounts for a gradual release and uptake of water rather than constant changes based on the concept of specific yield. Small differences between the computed values of the three water table recoveries, each one starting at a different degree of drainage in the zone above the water table, are probably due to the relatively small unsaturated portion of the aquifer profile.