Abstract
The area where there is large discharge subsurface flow over an impermeable layer was defined in this study as variable source area (VSA). The component of water flowing slowly was not considered. An equation for determining the moving boundary of this VSA was derived. It was found to be applicable to an one?dimensional unsteady model.
In this derived equation, there is only one unknown parameter which is the ratio of water depth (i. e., water volume per unit area affecting direct run?off) to discharge per unit width. So it is possible to determine both the moving boundary and Darcy's flow in VSA using this unknown parameter.
The following assumptions must be made for run?off analysis. The first is effective rainfall. All rainfall into VSA is effective. The second is increasing velocity of VSA. In this paper, a term related to this increase was considered to-be linearly related to rainfall intensity and to the len gth of the no-source area. The third is that water depth is related to discharge. Water depth was considered to be linearly related to discharge.
A reclaimed terraced field made by cutting and banking a clay hill-slope was used for this research. A clay layer was under the plow layer or the banking, thus the first assumption was justified to some degree. Inverse analysis of run-off discharge indicated the second assumption to be essentially valid. The simulated response of peak discharge was slow compared to the that measured values.
