Integrated River Management - River Dynamics and Integrated River Management - page 759

Fig. 11.44 Distribution of annual runoff and sediment load along the course of the Yangtze River (The points are
the average value for the period of 1950-2000 with data measured at the stations)
The middle and lower reaches of the Yangtze River are alluvial and the sediment load varies in
accordance with the sediment carrying capacity of the flow. Figure 11.45 shows the relations between the
total sediment load and water discharge at the Yichang, Hankou, and Datong stations in different seasons.
At Yichang (upper reaches), the sediment load is always proportional to the flow discharge because both
sediment and water are from the upper reaches. At Hankou and Datong (middle and lower reaches),
however, the sediment load is proportional to the flow discharge in the low flow season from October to
June, but the load is not related to the discharge in the flood season from July to September. In the
middle and lower reaches, sediment consists mainly of bed material load in the low flow season. The
higher the flow discharge, the more sediment is eroded from the channel bed, and, therefore, the higher
the sediment load. In the flood season, however, a lot of sediment is transported from upstream reaches
but half of the water is from the middle and lower reaches. Sediment and water are from different reaches
and a huge amount of sediment load is wash load, therefore, the sediment load is not strongly related to
the flow discharge.
Fig. 11.45 Relations between the monthly sediment load and monthly average flow discharge at Yichang, Hankou
and Datong in the low flow season (January to March) and the flood season (July to September) ( r n is the correlation
coefficient of these relations)