Water and sediment evolution in areas with high and coarse sediment yield of the Loess Plateau

In the past few years, the amount of sediment entering the Yellow River decreased significantly in areas with high and coarse sediment yield of the Loess Plateau. Some researchers considered that it was owing to the soil and water conservation project, while others believed that it was caused by the low precipitation. The observation data showed that the ultimate soil erosion modulus in 1960s could reach 150,000 t km^?2. However some experts preferred to believe that the ultimate soil erosion modulus in 1960s was wrong due to some uncertain mistakes. This paper quantitatively analyzed the spatial-temporal evolution pattern of sediment yield in areas with high and coarse sediment yield of the Loess Plateau over the past 50 years, by simulating the precipitation-runoff and soil erosion in 12 sample years with the digital watershed model. Some preliminary conclusions have been drawn as following: since the 1960s and 1970s, the rainstorm center had moved southward and the intensity of rainfall center became weaker and spread into dispersed rainfall distribution in areas with high and coarse sediment yield; the decrease of the amount of sediment entering the Yellow River was caused by the changes of rainfall type in recent years; the rainstorm of 1967 was concentrated in the region nearby “Shenmu-Fugu” in Shaanxi Province, and the annual maximum transport modulus (150,000 t km^?2) measured in Bullpen Ditch of the left bank tributary between “Shenmu” and “Fugu” in 1967 is reasonable.