Title:
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Sediment dynamics and sources in the Jinshajiang catchment, Upper Yangtze basin, China
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The sediment sources and yield of the Jinshajiang basin, the largest tributary in the
upper Yangtze basin are of major significance for the exploitation of the water
resources of China's largest river. At Pinshan, the outlet gauging station, the area
of the Jinshajiang catchment is 485,500 km2 and the mean annual discharge is
4430 m3 s- I or 32.1 % of that at Yichang, just below the Three Gorges Dam site.
The mean annual sediment load at Pinshan of 247 million tonnes is 47.1 % of that
at Yichang.
The sources and delivery of sediment in the Jinshajiang are assessed in the
framework of a catchment system which looks at the interplay of hydrometeorological,
terrain, vegetation, and human land use factors. The key factors in
the present pattern of soil erosion and sediment delivery are: rainfall, topography,
slope characteristics, vegetation cover, land use, soil properties and the duration
and areas of storm cover. The main sediment sources are in the lower sector of the
Jinshajiang, particularity
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the reach from Dukou to Pinshan, with a local catchment
area of 61,897 km2 : L"
, an average annual runoff of 25.88xlO9 m3 and an average
annual sediment load of 54.6 million tonnes. These quantities mean that this reach
representing only 12.8 % of the area above Pinshan, supplies 18.1 % of the runoff
and 62.6 % of the sediment load. The high sediment load comes from both the
steepness of the terrain and the intensity of agricultural land use. No clear time
trend in the sediment yield of the Jinshajiang emerges. Some tributaries have
decreasing yields, perhaps due to sediment deposition in reservoirs, while others
exhibit an increasing trend, in some cases due to increased agricultural pressure on
the land, and also to construction and engineering activities which cause high
sediment yields for short periods of time at individual localities.
The pattern of change sediment discharge has been modelled using a distributed
rainfall: runoff and runoff: sediment model using data on precipitation, evaporation
and proportion of forest cover (land use). The model has been tested against the
daily discharge and sediment yield of the 3074 km2 Heishuihe catchment and the
1607 kM2 Meigu catchment.
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