Impacts of terracing on hydrological processes: a case study in Wangmaogou watershed of the Loess Plateau

The Loess Plateau of China is known for its severe soil and water loss problems. Terracing is one of the most important soil and water conservation measures there. Our understanding of the effects of terraces on soil and water conservation and its mechanism is limited by observation data on runoff and soil erosion as well as the influences from local environmental characteristics. In this study, we applied a physically-based distributed hydrological model (Integrated Hydrology Model, InHM) to an experimental terrace in Wangmaogou watershed of the Loess Plateau, and validated it with the measured soil water content. Our results suggested that terrace construction can substantially reduce runoff by changing the flow direction, especially during heavy rainfall events. This reduction in runoff would be greatly attenuated when ridges are damaged due to lack of maintenance. Under the rainfall intensity of 120 mm/h, compared with hillslope, a well-maintained terrace could reduce runoff by 100%, while the terrace without ridges could only reduce 28% runoff. Besides, ridges not only prevented water from flowing out of platforms, but also helped maintain the risers from terrace failure by decreasing about 20% of the saturation rate at the risers. Our results also emphasized the importance of evaporation, which could make up to 15% of the total water loss even during the rainfall events. Given the effects of terraces on water conservation, it is essential for the land use management of the Loess Plateau to take into account of the terracing approach, as well as a good maintenance of ridges.