The effects of rainfall regimes and rainfall characteristics on peak discharge in a small debris flow-prone catchment

Abstract

Peak discharge plays an important role in triggering channelized debris flows. The rainfall regimes and rainfall characteristics have been demonstrated to have important influences on peak discharge. In order to explore the relationship between rainfall regimes and peak discharge, a measuring system was placed at the outlet of a small, debris flow-prone catchment. The facility consisted of an approximately rectangular stilling basin, ending with a sharp-crested weir. Six runoff events were recorded which provided a unique opportunity for characterizing the hydrological response of the debris flow-prone catchment. Then, a rainfall-runoff model was tested against the flow discharge measurements to have a deep understanding of hydrological response. Based on the calibrated rainfall-runoff model, twelve different artificially set rainfall patterns were regarded as the input parameters to investigate the effect of rainfall regimes on peak discharge. The results show that the rainfall patterns have a significant effect on peak discharge. The rainfall regimes which have higher peak rainfall intensity and peak rainfall point occur at the later part of rainfall process are easy to generate larger peak discharge in the condition of the same cumulative rainfall and duration. Then, in order to explore the relationship between rainfall characteristics and peak discharge under different cumulative precipitation and different duration, 167 measured rainfall events were also collected. On the basis of rainfall depth, rainfall duration, and maximum hourly intensity, all the rainfall events were classified into four categories by using K-mean clustering. Rainfall regime 1 was composed of rainfall events with a moderate mean P (precipitation), a moderate D (duration), and a moderate I60 (maximum hourly intensity). Rainfall regime 2 was the group of rainfall events with a high mean P, long D. Rainfall regime 3, however, had a low P and a long D. The characteristic of Rainfall regime 4 was high I60 and short duration with large P. The results show that the rainfall regime 2 and 4 are easier to generate peak discharge as the rainfall intensity plays an important role in generating peak discharge. The results in this study have implications for improving peak discharge prediction accuracy in debris flow gully.