Effect of Comprehensive Management on Runoff and Sediment Reduction in Yanwachuan Watershed, Loess Tableland, China

摘要

To evaluate the effect of comprehensive management on runoff and sediment reduction in meso-scalewatersheds, the Yanwachuan watershed of Loess tableland gully region in China was investigated. Variationtrends of the runoff and sediment from 1981 to 2009 were analysed, and the year of abrupt changewas identified using the double mass curve method, accumulative departure method, moving t-testmethod and Yamamoto method. Next, the effects of comprehensive management on runoff andsediment reductions were quantitatively evaluated based on the runoff/sediment coefficient methodand double mass curve method, both capable of separating the effect of climate change from that ofcomprehensive management. Finally, the driving forces of runoff and sediment variations werediscussed from both climatic and comprehensive management aspects. The results showed that therunoff and sediment in the watershed had significantly decreased since an abrupt change in 1997.During the change period (1998-2009), the erosive precipitation and precipitation erosivity had beenreduced by 32.4% and 17.4%, respectively, compared with the base period (1981-1997); the areas offorest and grass had increased; and the normalized difference vegetation index (NDVI) had increasedby 20.6% with significantly enlarged vegetation coverage. The benefit value of runoff reduction andsediment reduction were 27.3% and 76.2%, respectively. The resultant runoff and sediment reductionsin the watershed were the synergy of climate change and comprehensive management, with greaterthan 90% reduction contributed by comprehensive management. All these results supported thatcomprehensive management played the dominant role in runoff and sediment reductions..