Analysis of variation in river sediment characteristics and influential factors in Yan'an City, China

Yan'an is an area in China experiencing serious soil erosion. It is important to have a good understanding of the variation in river sediment characteristics and influencing factors for soil and water conservations. We use Mann–Kendall and Pettitt methods to examine the effects of precipitation and human activities on the water sediment in the Beiluo and Yanhe rivers in Yan'an City, China from 1980 to 2012. The results show that between 1980 and 2012, the mutation points in the runoff data for the Beiluo and Yanhe Rivers occurred in 2002 and 2004, respectively. The quantities of runoff during the mutation periods in the two rivers are 27.46 and 42.26% less than they are in the base periods, respectively. Sediment-concentration mutation points occur in 2006 and 2003, and the sediment concentrations during the mutation periods are 80.45 and 58.26% less than they are during the base periods, respectively. The proportions of decrease in runoff due to precipitation factors are 13.83 and 25.42%; hence, the proportions attributed to human activity are 86.17 and 74.58%. The decreases in the sediment concentration are 13.40 and 14.43% due to precipitation. The remaining 86.60 and 85.57% are attributable to changes in human activities. The water sediment mutation points occurred during the implementation of the Return Farmland to Forest Program. The observed changes in hydrological factors may be due to decreased soil erosion and surface runoff because of increased vegetation coverage after the implementation of the project. These findings will be useful for water and soil conservation.