Numerical investigation of saturated source area behavior at the small catchment scale

The objective of this research is to explore the relationship between small catchment properties and the temporal growth and decay of saturated source areas (SSA). A simple physics-based hydrologic model, which we call the Sandbox model, is developed for this purpose. A thorough sensitivity analysis is undertaken to evaluate model response to variations in model parameters. Sandbox model output is compared to that from the semi-distributed conceptual model, TOPMODEL, a model with a wide spread acceptance. Plotting the temporal evolution of the extent of saturated source area versus catchment average soil water content during a number of wetting and drying cycles shows a wide variety of trajectories or hysteretic loops. A parametric analysis was performed to quantify the impact of hypothetical catchment properties on the relationship between saturated area extent and basin-average soil water content, revealing hysteretic behavior. It is shown that this hysteresis is the result of changes in groundwater table slope, which is usually less than, and seldom equal to, the land-surface slope in non-saturated areas.