Unsaturated flow properties used to predict outflow and evapotranspiration from a sloping lysimeter

Abstract

Field measurements of sou moisture content and pressure potential were used to determine the moisture flux, hydraulic gradients, and dynamic conductivity of a 200‐foot sloping soil lysimeter. These measurements were then used to predict outflow and evapotranspiration. A vertical unsaturated Darcian analysis was used to evaluate conductivity during the first study phase, in which evapotranspiration was eliminated by sealing the model surface with a plastic sheet. The moisture flux term in the Darcy equation was determined by evaluating moisture content change in depth and time. Moisture flux determined in this way agreed with measurements of actual outflow. Conductivities were solved from flux and hydraulic gradients, and corresponding water contents were assigned. Conductivity curves were highly significant and agreed with those obtained when the model was uncovered. Evapotranspiration was solved during the second study phase (cover removed and grass established) by using a water balance based on moisture content and potential, rainfall, and conductivity (from the first study phase). Results at the deepest level in the profile agreed well with those based on actual outflow.