2002 Volume 46 Pages 163-168
A mountainous drainage basin with forested soil is considered as a lowpass filter. Unsaturated flow equation is frequently substituted for runoff system in a mountain slope. This substitution is based on the analysis of actual rainfall-runoff phenomena there. This paper adopts a two-dimensional unsaturated flow equation as runoff system and theoretically derives its equivalent frequency transfer function. The validity of the proposed function is cross-checked by a simulation method. By using this function, it is possible to estimate a gain characteristic of substituted runoff system. The analytical result using frequency response method by the gain characteristic shows the response characteristic of this system for arbitrary rainfall input.
