Check dam and its functions on the Loess Plateau of North Shaanxi Province, China

The Loess Plateau is one of the most severe soil erosion area worldwide, and the north Shaanxi Loess Plateau is the main sediment source of the Yellow River. The functions of check dam are analyzed based on the data of land use and land cover change, hydrological process and filed survey on soil property and yield. The average annual soil erosion rate in this region varied from 8000-10000 ton per square kilometer before 1980s and reduce to 2000-4000 ton per square kilometer in recent years. The check dam is one of the most important practices of soil and water conservation in this region. It has a long-term history inspired by the natural dam caused by great landslide in 1969 of Ming Dynasty and developed very fast since 1960s. The functions of check dam cover the whole soil erosion process, sediment and flow of the branches and the Yellow River, agricultural production, soil carbon consequence, and local climate regulation. There were about 33.9 thousand check dams in this region, and the sedimentation in the check dams is around 5.9 billion tons that the average annual reduction of sediment load of the river accounted for 3000-5000 ton per square kilometer in their formation period of 20 to 30 years. The current check-dam land was about 57.3 thousand hectors with very good fertility condition and soil moisture because of the deposition induced by soil erosion of the topsoil and seasonal flashflood in the catchment. The average yield on the check-dam land could be 6000-15000 kg per hector in the semiarid cropland, about 3-10 time of that on the slope, that could reduce the cultivation on the slopes for more food demands and the relating soil erosion generation. The soil moisture retained in the check dam were estimated to about 2 billion ton annually and the SOM in the whole profile of check-dam land could be 3 times high than that in the top-soil layer (less than 1g/kg). The reduction of sediment load in the Yellow River could save a great amount of capacity of reservoirs, decrease the rising of the riverbed and flood risks of the lower stream of the Yellow River, and it also could save 1-3 billion cubic meters of runoff to flush the sediment away into the Bohai Sea. The functions of check dam could be sustainable if well-maintained.