Integrated River Management - River Dynamics and Integrated River Management - page 755

tons per year (Tang, 2004). But the sediment load measured at Yichang is only about 500 million tons per
year. Thus, large volume of sediment is stored somewhere in the upper reaches.
Fig. 11.42 The Yangtze River Basin, showing the locations of hydrological stations, meteorological stations, tributaries,
riparian lakes, the debris flow areas; and the watershed topography on an east-west line from Batang through Chongqing
and Poyang Lake to the East China Sea
Soil erosion, sediment load, and sediment storage have been measured and the data have been analyzed.
There are many hydrological stations and numerous monitored cross sections and gauging stations on the
river and its tributaries. Regular measurements are performed daily at the hydrological stations, including
stage, velocity, discharge, suspended sediment concentration, and the rate of bed load transportation. The
later is measured by using bed load samplers. Channel bed deformation is measured occasionally at all
stations and at the monitored cross sections on the rivers, ravines, and gullies. The sediment load of the
river is calculated with the flow discharge, suspended sediment concentration, and rate of bed load
transportation. Because the bed load is less than 1% of the total load, the relatively large error in bed load
measurement does not affect the accuracy of the total sediment load measurement. The volume of
sediment deposition on the riverbed and reservoirs is calculated with the measured cross sections.
Soil erosion is measured in the following ways: (1) the soil erosion areas are determined by field
investigations; (2) for each soil erosion area, the rate of sediment load transportation is measured at the
downstream end of the small wartershed (generally several tens to a hundred square kilometers); (3) the
rate of sediment erosion is calculated with the total load per year over the area of the watershed; or (4) the
rate of soil erosion is directly measured by collecting the sediment eroded from a 100 m 2 sample plot,
which is isolated by using low steel plate walls during rainfall; and (5) the amount of soil erosion from all
small watersheds is summed to obtain the total amount of soil erosion from the basin.
The total amount of soil erosion from the upper Yangtze River Basin is reported at 1.6-2.24 billion
tons per year, depending on the statistics. (Yu et al., 1991) evaluated the statistics and reported the total