Analysis of the Relationship between Soil Erosion Risk and Surplus Floodwater during Flood Season

Soil erosion can lead to an increase in the concentration of sediment in the runoff and the surplus floodwater during flood season, which increases the likelihood of a flood disaster. To analyze the relationship between the risk of soil erosion and the surplus floodwater during flood season, a case study of the Jinghe River Basin located in the middle Loess Plateau of China was performed. A measure of the soil erosion risk R-e was presented, which combined the five factors in universal soil loss equation (USLE) with information entropy theory. The results show that the northern watershed features both high and severe levels of soil erosion risk, especially the watershed controlled by the Qingyang (QY) station, whereas the risk level is low or slight in the southern Jinghe basin, the Ziwuling Mountains in the east, and the Liupanshan Mountains in the west. Compared with the USLE, the R-e measure can better reflect the spatial distribution of soil erosion risk and identify the areas corresponding to different soil erosion levels. Data for the sediment yield rate from 37 subbasins also prove the correctness of the R-e measure. The results from a sensitivity analysis indicate that the same amount of factor variability led to a larger soil erosion risk increment in 1986, followed by those of 2000 and 1995. The magnitude of the influences of the R, C, P, and LS factors on the soil erosion risk features a descending order of R > C > P > LS. The regression analysis reveals a statistically significant linear relationship between the coefficient of surplus floodwater and the level of soil erosion risk. The higher level of soil erosion risk can cause more surplus floodwater downstream when the sediment concentration is smaller than the limit of the sediment concentration for river water use. The limit also has important influences on the amount of surplus floodwater during flood season. (C) 2014 American Society of Civil Engineers.