Modeling the impacts of integrated small watershed management on soil erosion and sediment delivery: A case study in the Three Gorges Area, China

Abstract

Summary Soil erosion poses a serious problem for sustainable agriculture and the environment. Owing to long-term anthropic pressure including overuse and inappropriate development, soil erosion has become a serious issue in the Three Gorges Area (TGA), China. Recently, integrated small watershed management (ISWM) for soil conservation in the TGA was rapidly developed. This study was conducted to investigate the impact of ISWM on soil erosion and sediment delivery in the Wangjiaqiao watershed in the TGA. The WATEM/SEDEM distributed erosion and sediment transport model was used to evaluate the effectiveness of the ISWM project. The model was calibrated against long-term measured suspended sediments at the watershed outlet. Land use and conservation measures were mapped and analyzed for 1995 and 2005, paying particular attention to quantification of changes in soil erosion and sediment delivery due to ISWM. The results showed that a combination of decreased soil loss (from 18.5 t ha −1 y −1 in 1995 to 13.2 t ha −1 y −1 in 2005) and increased sediment deposition (from 7.7 to 12.4 t ha −1 y −1 ) has led to a strong decrease in sediment yield (from 8.4 to 3.9 t ha −1 y −1 ) and the sediment delivery ratio (from 0.454 to 0.295). The results of scenario analysis showed that soil conservation measures taken in fields effectively reduce on-site soil loss and sediment yield. However, off-site sediment control measures appear to be much less effective at reducing sediment yield. This diachronic comparison of soil erosion and sediment delivery revealed that ISWM is quite effective and efficient; therefore, it is the appropriate method to combat soil erosion in the TGA and similar areas.