Modeling Surface and Subsurface Stormflow on Steeply-Sloping Forested Watersheds

Abstract

Abstract: A simple conceptual rainfall-runoff model, based on the variable source area concept, was developed for predicting runoff from small, steep-sloped, forested Appalachian watersheds. Tests of the model showed that the predicted and observed daily discharges were in good agreement. The results demonstrate the ability of the model to simulate the "flashy" hydrologic behavior of these watersheds. Five subsurface flow models were evaluated by application to existing data measured at Coweeta on a reconstructed homogeneous forest soil. The five models were: Nieber 's 2-D and 1-D finite element models (based on Richards' equation), the kinematic wave equation, and two simple storage models developed by the authors, the Boussinesq and kinematic storage models. All five models performed reasonably well on this homogeneous soil. The coupled infiltration model had a large effect on the simulation results. The cost of running the computer models and the computer memory requirements increased as their complexity increased. Field soil-water and precipitation measurements were made on a small test plot in Robinson Forest, in Eastern Kentucky. These data were used to calculate runoff during four precipitation events and to test three of the subsurface flow models on a natural watershed. Of the models tested, the simple kinematic storage model performed the best. Flow from the test plot was dominated by macropore flow during storm events, and by flow through the soil matrix during baseflow or recession periods. No surface runoff was observed on the test plot during the period of field observations, except on the saturated near-channel source areas; all runoff was initiated by subsurface flow. Funding information: The work upon which this report is based was supported in part by funds provided by the United States Department of the Interior, Washington, D.C., as authorized by the Water Research and Development Act of 1978. Public Law 95-467. Thanks is also expressed to the College of Agriculture for providing supplementary financial support for this project.

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