Modeling Surface and Subsurface Runoff in a Forested Watershed

A hydrologic model, capable of approximating surface and subsurface runoff from a forested shallow-soil watershed without the time of concentration parameter, is developed. A watershed is modeled as a series of vertically and horizontally linked nonlinear storages, each represented by a lumped mass-balance equation. The resulting system of ordinary differential equations is evaluated by the fourth-order Runge-Kutta finite-difference method. Comparison of this simpler modeling approach with method of characteristics and Petrov-Galerkin finite-element solutions shows good agreement. However, because the performance of the preliminary formulation on a forested watershed was unsatisfactory, an extended subsurface model is developed that explicitly accounts for the presence of both the soil and the small channels between the soil layer and bedrock face. Application of the extended model to the same forested watershed shows significantly improved agreement between the observed and computed runoff hydrographs.