Study On Rainfall-runoff Process And The Simulation In The Watershed On The Loess Plateau

In this paper, rainfall runoff processes are analyzed with hydrology, meteorology and land use materials in Caijiachuan watershed on Loess Plateau, China. In addition, HEC-HMS hydrology model is embedded in ArcView software (GIS) to simulate the rainfall runoff process.The results show that storm event with short duration and high intensity is predominant rainfall type in the earea, although the rainfall amount is relative low. Large storm events with long duration and low intensity account most of the total precipitation for the high rainfall amounts. During the rainfall events, max rainfall amount in 10mins is the most important parameter influence the rainfall runoff process. In storm events with short duration and high intensity, runoff depth, runoff coefficient and peak flow are highest in artificial forests watershed, and lowest in agricultural watershed., on the other hand, runoff depth, runoff coefficient and peak flow in natural forests watershed are significantly lower than the unforested watershed. In large storm events with long duration and low intensity, runoff depth, runoff coefficient and peak flow are highest in artificial forests watershed, and runoff depth and runoff coefficient are lowest in agricultural watershed with peak flow only higher than natural and artificial forests watershed. In the other type rainfall events, runoff depth, runoff coefficient and peak flow are lowest in natural forests watershed, and runoff depth and runoff coefficient are highest in farmlands and grasslands watershed with peak flow is only lower than artificial forests watershed. In storm events with short duration and high intensity, runoff depth, runoff coefficient and peak flow in the watershed are higher than that in other type rainfall events which means water and soil loss is serious.In HEC-HMS hydrology model built up in this research, CN value is the predominant parameter, influences rainfall runoff amounts and peak flow. As CN value rises, rainfall runoff amounts and peak flow increase. During calibration period, R2 value ranges from 0.75 to 0.87, r value ranges from 0.84 to 0.94, and in validation period, R2 value ranges from 0.73 to 0.82, r value ranges from 0.82～0.94. So, it is clear that HEC-HMS hydrology model could be built up properly in the experimental area.In addition, the HEC-HMS hydrology model is used to simulate rainfall ruoff process under different forest cover rates and distributions, the results of simulation show that rainfall runoff and peak flow decreases as the forest cover rate rises, and lower when forests distribute in upstream area.