A Saturated Excess Runoff Pedotransfer Function for Vegetated Watersheds

Abstract

Since Hewlett and Hibbert's publication in 1967, there has been a slow recognition that saturated excess runoff is the main runoff mechanism in vegetated watersheds. Yet, most pedotransfer functions for predicting runoff are based on infiltration excess runoff. We, therefore, developed a simple pedotransfer function to predict saturation excess runoff, using data from eight watersheds on three continents. The runoff response was very similar for all watersheds, despite differences in climate, size, topography, and land use. Direct storm runoff occurred after a threshold amount of rainfall was exceeded. Runoff was linearly related to rainfall depth, indicating that a nearly constant proportion of the watershed was the source area. Size of source areas decreased with increasing depths of soils. The rainfall threshold was strongly dependent on the initial moisture conditions. The developed pedotransfer function for saturation excess runoff was used to predict water level fluctuation of two terminal lakes on the Caribbean Islands over a 25‐ to 30‐yr period with the rainfall threshold computed following Thornthwaite–Mather and baseflow from the remaining part of the watershed employing a linear reservoir model. Taking the simplicity of the prediction technique with only four calibrated parameters into account, lake levels were predicted reasonably well to very good, including the rise in the lake level in the last 10 yr when the climate in the region became wetter. It is expected that the linear relationship of rainfall and runoff holds for storms lasting several days and can simplify flood predictions.

Impact of Soil Depth and Topography on the Effectiveness of Conservation Practices on Discharge and Soil Loss in the Ethiopian Highlands

“…Finally, our findings agree with [38,54] in that soil depth is highly significant in controlling the portion of flow, i.e., direct runoff and base flow. As the depth of soil increases, interflow and base flow increase.…”

“…The greater discharge in the shallower watershed agrees with saturation excess runoff theory, where the portion of saturated soil increases for a given storm with decreasing soil depth. This results in more direct runoff generated, shortening the residence time in the watershed and consequently leading to less evapotranspiration from the rainwater [38,39].…”

Improving efficacy of landscape interventions in the (sub) humid Ethiopian highlands by improved understanding of runoff processes

“…For deep soils without restrictive layers, the source area is a relatively small part of the watershed Steenhuis et al, 2013). The opposite is true for watersheds with restrictive layers that have larger contributing areas and less baseflow.…”

Effect of Hydrograph Separation on Suspended Sediment Concentration Predictions in a Forested Headwater with Thick Soil and Weathered Gneiss Layers

“…For these reasons, changes of the groundwater level in the source area are small, and a riparian zone can be considered almost the same as the source area. This differs from other forested catchments where the source area expands more significantly than the usual riparian zone, for example, where the saturated throughflow dominates runoff generation in weathered granite catchments [30,31] or in normal vegetated catchments [32]. The spring water is provided by groundwater flow through the weathered gneiss layer [33].…”