Analysis of the Soil and Water Conservation Measures Reducing Runoff and Sediment in the Datong and Pingluo River Basins

The Datong River is the fourth order tributary of the Jialing River.The river basin lies in humid semitropical monsoon climate region with a catchment area of 160 000 km 2.The Pingluo River is one of the largest tributaries of the Xihanshui River with a catchment area of 741 km 2.The climate condition of the Pingluo River basin is different from that of the Datong River.It has arid climaate and less precipitaion.Both river basins are typical catchments of the Jialing River with different geological,physiographic and climatic conditions.They are the main sediment sources of the Jialing River basin.After implementation of the soil and water conservation measures in the upper Yangtze River,the total area that has brought under control reached 25.8 percent of the total soil and water loss area before 1996.The soil and water losses have been greatly reduced.The change in runoff,sediment,and their relationship are analyzed on the basis of measured hydrologic data in the two typical catchments of the Jialing River.