Impact of soil and water conservation practices on sediment particle size in the Yanhe River, China

The sediment particle size is influenced by multiple factors and plays a very important role in reservoir management and landform change of the river system. The change of sediment particle size and factors affecting it were analyzed based on data of annual coarse sediment flow, monthly sediment particle size, annual and monthly precipitation and soil conservation practices in the Yanhe River and its basin. The coarse sediment flow decreased from 1963 to 1984, and on the whole, the median particle diameter and mean particle diameter got smaller gradually. The trends of annual precipitation change in each county did not match with that of the annual coarse sediment flow change, which means that the annual coarse sediment change is not the result of annual precipitation change. The trends of precipitation change during several months and in the flood period showed that the precipitation changes are not as uniform as that of the sediment particle size. Land use change and soil and water conservation in the Yanhe River are most likely the main reasons for the change of sediment particle size.