The Loess Plateau of China suffers from severe soil erosion. In the gullied rolling loess region, approximately half of the sediment derives from gully areas, which are the most prominent topographical features of this region. No existing soil erosion models are appropriate in accuracy or applicability for the Loess Plateau because existing models only consider slope and river erosion processes at the catchment scale. The absence of the gully erosion process in these models significantly limits their application to the Loess Plateau. Taking this issue into account, a three-process-based distributed soil erosion model, denoted by WEP-SED, is proposed to investigate soil erosion in this region based on the Water and Energy transfer Processes in Large river basins (WEP-L) model. In WEP-SED, a sequential “slope-gully-river” structure is built for the physically-based simulation of soil erosion and sediment yield. In this structure, soil erosion is integrated from six parts with successive transport relationships. The proposed model is applied to the upstream region of the Wenjiachuan hydrological station in the Kuye River basin. The simulated monthly average sediment transport rates from 1956 to 2010 at the Wenjiachuan hydrological station agree well with the observations, with a correlation coefficient of 0.76, an NSE of 0.58, and a relative error of −5.60%. Furthermore, the simulated average annual amount of gully erosion reaches 60.30% of the total soil erosion, reflecting the fact that the gully erosion is a serious problem and demonstrating that gully erosion must be considered separately in this area.
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