Effect of Hillslope Structure and Recharge Rate on Formation of Saturated Area

Abstract:

Saturated areas play a key role in many hydrological processes. The free water storage capacity controls the formation of the saturated area and it is usually estimated by empirical calibration in lumped hydrological models or assigned a maximum value in distributed hydrological models. In fact, the hillslope structure appears to be a significant control over stormflow and saturation. Adopting the kinematic wave equation to describe subsurface flow, we derived analytical solutions of hillslope free water storage capacity of different configuration and recharge rate. Comparison with numerical solution of Boussinesq equation shows the accuracy of analytical solutions. This study examines the relative importance of hillslope structure (bedrock gradient and profile curvature) and recharge rate on free water storage capacity and saturated areas. Results indicate that high recharge rate, gentle bedrock gradient and concave profile curvature are conducive to the formation of saturated area. Saturated area is much larger on milder slopes than on the steeper slopes, and increases with the increase of recharge rate. The effect of profile curvature on saturated area is affected by recharge rate. There is a special recharge rate for each bedrock gradient. When the recharge rate is less than it, the saturated area of concave slope is larger; when the recharge rate is greater than it, the saturated area of concave slope is larger. In addition, we quantified the critical recharge rate and critical storage capacity, which are the minimum recharge rate required to generate saturated area and the storage capacity at this recharge rate. These analytical solutions link hillslope hydrological knowledge with hydrological models and contribute to the development of hydrological models parameterization.