Abstract
The objective of this study is to quantify the changes in the coefficients of peak discharge (fp) with reference to the long-term natural recovery of forests on denuded hills. The Ananomiya experimental watershed at the Ecohydrology Research Institute (the University of Tokyo Forests) was selected for this study. We compared the relationship between fp and discharge when the discharge trend changed from decreasing to increasing (Qi), and from the onset of precipitation to the time when peak precipitation (Pi) was attained. This was done in order to estimate peak discharge during an early 11-year period and a late 22-year period. Regardless of whether measurements were taken during early or late periods, the fp increased when the Pi increased. Conversely, the relationship between fp and Qi, an indicator of the wetness condition of the watershed, was not clear. The maximum fp values during the late period, when Pi was 0, 25, and 50, represented a decrease of 53, 45, and 42%, respectively, with respect to the corresponding figures from the early period. This study showed that fp of a heavy precipitation event referred to as the Tokai Heavy Rain event (total precipitation of 401.5 mm), was 0.58, far below 1.0.
