Effects of varying the spatial configuration and scale of terraces on water and sediment loss based on scenario simulation within the Chinese Loess Plateau

To optimize soil and water conservation measures, it is important to consider the spatial configuration and construction scale of terraces on the Loess Plateau in China. However, there are few existing efficient technology frameworks for assessing the impact of changing the spatial configuration and scale on reducing water and sediment loss at the basin scale. To address this gap, this study proposes a framework that employs a distributed runoff and sediment simulation tool coupled with multi-source data and scenario setting methods to identify the impacts of constructing terraces with different spatial configurations and scales on reducing water and sediment loss at the event scale on the Loess Plateau. Four scenarios (i.e. baseline, realistic, configuration changing and scale changing scenarios) were established to evaluate the associated impacts. The results show that, under the realistic scenario, the average water loss reductions within Yanhe Ansai and Gushanchuan Basins are 15.28 % and 8.68 %, respectively, and average sediment reduction rates are 15.97 % and 7.83 %, respectively. The effect of reducing water and sediment loss in the basin is highly related to the spatial configuration of terraces and that terraces should be built as low as possible on hillslopes. The results also show that, if terraces are disorderly constructed, the threshold of the terrace ratio that effectively contains the sediment yield in the hilly and gully regions of the Loess Plateau is approximately 35 %, whereas if the scale of terraces is increased, the sediment reduction effect is not significantly improved. Furthermore, if terraces are configured near the downslope, the threshold of the terrace ratio that can effectively contain sediment yield is further reduced to approximately 25 %. This study can be used as a scientific and methodological reference for optimizing terrace measures at a basin scale in the Loess Plateau and in other similar regions in the world.