Diagnostic Analysis of Runoff Generation Processes based on rainfall-runoff events in Middle Yellow river Basin: The Gushanchuan River

This paper presents the results of a diagnostic study of short time runoff generation processes in the Gushanchuan basin, located in the Middle yellow river basin, Northern China. This study involves analysis of signatures of temperal rainfall and runoff variability of flood events, vegetation change and diagnostic analysis on runoff generation mechanisms based on the change of underlying surface conditions, extracted from observed rainfall-runoff data of 125 flood events and remote sense data. Three stages were divided according to the surface conditions of the watershed, 1965-1979, 1980-1998 and 1999-2006. Analysis of observed data indicates that the multi-rainfall events duration were among 20~24 hours, the average rainfall of every stages is 69.6mm, 55.4mm and 24.8mm, respectively. And the coefficient of correlation between rainfall intensity and runoff were about 0.59, 0.62 and 0.51, respectively. The flood hydrographs present steep rise and steep fall, slow down, and sustained rises slow down , which means that the flow components of hydrograph are made up of more runoff components, saturation excess flow, infiltration excess flow, interflow and groundwater flow. There were different components in different rainfall-runoff events. And contributing to runoff generation mechanisms from infiltration excess runoff, saturation excess runoff, and mixed saturation and infiltration excess runoff. But infiltration excess runoff mechanisms are the dominant mode. And saturation excess runoff and mixed saturation and infiltration excess runoff coexists with the change of vegetation cover in a way. The forest area were increased by 27.82% from 1965-1979 to 1999~2006. This competition is quantitatively shown to be controlled by the relative magnitudes of vegetation cover. The capacity of soil storage increase with the raising amount of vegetation cover. In addition, the spatial variabilities of vegetation cover also impact the behavior of runoff generation process.