Abstract:
There is an increasing trend of extreme rainfall events in the background of changing environment, it is of great practical significance to analyze the rainfall-runoff relationship in different storm flood events. The Liangshui River Basin, which is one of the four main drainage basins in Beijing, is the study area in this study. The storm of “7.21” in 2012, which can represent the short duration bimodal storm, and the storm of “7.20” in 2016, which can represent the long duration bimodal storm, are selected as the typical cases here, and the rainfall-runoff relationship are analyzed. The proportion of impermeable area is the key control condition of the flood process. The high proportion of the impervious area in the upper reaches of the Liangshui River Basin can accelerate the rate of regional flooding process, makes the response of the runoff to storm more sensitive, and finally causes the rapid change between flood and storm. In the lower reaches of the basin, the consistency of the rainfall-runoff sequence is weakened due to the relatively low impermeable area, the increase of the confluence area and the diversion effect in the process of river flooding. By the comparison of the runoff coefficients in the two storms, we can conclude that the relationship between rainfall and runoff is affected by three main factors, the impervious area, the total rainfall and the rainfall duration.Due to the relatively high impermeable area, the runoff coefficient in the upper reaches is around 0.35~0.5 with rainfall depth of 10 to 20 years return period. But in the lower reaches, because of the infiltration process, the runoff coefficient may decrease by more than 1/3 and 1/2 for lower reaches and whole Liangshui River Basin.
