Assessing the effects of soil and water conservation in gully land consolidation using the modified SWAT-Terrace model

To alleviate the competition for cropland between ecological restoration and agricultural production, a Gully Land Consolidation (GLC) project has been widely executed in the Chinese Loess Plateau. This project involves mechanically excavating slopes and filling gullies to expand cropland area. Therefore, in the context of climatic and topographical changes, an assessment of the impact of GLC as a key land use measure of water and sediment in space and time is urgently needed. However, due to scale effects, there is a lack of relevant assessments for the GLC. This study utilized the Soil and Water Assessment Tool (SWAT) and SWAT-Terrace model to analyze the temporal-spatial changes of water and sediment in the Yanhe watershed during 1985-1998 (R1) and 1999-2017 (R2). Additionally, it assessed the effectiveness of GLC in erosion control across different sub-basin clusters. The results showed that (1) at the temporal scale, the runoff and sediment decreased by 30.09 % and 72.73 % respectively, during R2 compared to R1; (2) at the spatial scale, 56 % and 71 % of the sub-basins located in the central and northern parts of the watershed showed a reduction in water and sediment yield, respectively, during R2 compared to R1, while the remaining sub-basins located in the southern part showed an increasing trend in water and sediment yield; and (3) the GLC can reduce 1.17 %-1.93 % of water yield and 0.94 %-1.91 % of sediment yield in the three clusters of sub-basins. The assessment of the soil and water conservation effects of the GLC is beneficial to policymakers in designing effective land management plans and the extension of the project to other regions.