Effect of soil and water conservation measures on the reduction of runoff and sediment load in a loess hilly-gully region

Soil and water conservation are important measures in regulating runoff and sediment load on the Loess Plateau. Information on how land use and land cover changes, especially the implementation of the soil and water loss control project, can affect the sediment load dynamics and hydrological variables is important since large-scale eco-environmental governance programs are being implemented. In this study, an improved double mass curve and the decomposition method were used to assess the effects of different soil and water control measures on runoff and sediment load in the Lvergou, which is a small basin on the Loess Plateau in China, based on 60 years of data. We conclude that the total precipitation (P) was not statistically significantly different (p > 0.05), whereas heavy rain increased significantly (p < 0.01). Annual runoff (R) and sediment load (S) decreased significantly from 1954 to 2010, with abrupt changes in 1990 and 1986. Sensitivity analysis indicates that P is more influential than temperature (T) in affecting R and S. This study indicates that soil and water conservation are the strongest contributors to reducing annual runoff and sediment load, with their contributions reaching 84.2% and 91.1%, respectively, while the remaining percentage was caused by climate variations. Among all soil and water conservation measures, the runoff and sediment load in the basin were most sensitive to the terrace. There were obvious changes in the rainfall-flood and rainfall-sediment relationships due to extreme rainfall conditions. Compared with historical extreme rainfall events, the decreases in flooding and sediment load in the river basin after 2000 under similar rainfall and intensity conditions were obvious. This result further indicates that the implementation of soil and water conservation measures plays an important role in reducing flooding and sediment load in this region by changing the water-sediment relationship during extreme rainfall. These results can provide important an reference for understanding the causes of sharp decrease of water and sediment in the Loess Plateau basin.