Impacts of terracing on hydrological processes: A case study from the Loess Plateau of China

Abstract

Terracing is one of the most important soil and water conservation measures on the Chinese Loess Plateau. 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, in the center of the Loess Plateau which attributed most of the sediment in the Yellow River. The soil water content were measured at daily scale for one month, while the simulations were conducted at second time step. 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 evapotranspiration, 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.