Integrated River Management - River Dynamics and Integrated River Management - page 761

The equilibrium bed profile is higher than the present profile and sedimentation dominates the fluvial
process of the middle and lower reaches. Still a huge amount of sediment is needed for the riverbed to
reach the equilibrium profile. Nevertheless, the volume of annual sedimentation in the middle and lower
reaches depends on the incoming load. Figure 11.47 shows the relation between the net sedimentation
(the volume of sedimentation minus erosion) and incoming sediment load from the upper reaches
(measured at Yichang) and the Hanjiang River, in which the sedimentation in Tongting Lake is not
included in the net sedimentation. The sediment load from Yichang and the Hanjiang River is more than
95% of the total sediment transported into the middle and lower reaches of the Yangtze River, to which
the total incoming load refers in the following text. The net sedimentation in the middle and lower
reaches increases linearly with the total incoming load. If the total incoming load is more than 280
million tons, sedimentation occurs in the river; if the total incoming load is around 500 million tons, 100
million tons of the sediment will deposit in the river. If there were no interruption by human activities,
the fluvial process to reach the minimum stream power would continue for a long period of time because
the present bed profile is still far from the equilibrium profile.

Fig. 11.47 Relation of the net sedimentation in the middle and lower Yangtze River with the incoming sediment load
from the upper Yangtze River (measured at Yichang) and the Hanjiang River

Tongting Lake is between Yichang and Wuhan, and is used as a flood diversion basin in the flood
season. If the sediment load at Yichang is more than 100 million tons, a part of the load will be carried
into Tongting Lake and deposit in the lake. The amount of sedimentation in the lake is proportional to the
incoming sediment load from Yichang. The sediment budget for the middle and lower reaches can be
summarized in the following formulas:

SS SSS (11.22)

Y H F T E

SkSSS ( ) (11.23)

F 1 Y H c 1

(11.24)
where S Y is the annual sediment load at Yichang; S H is the annual sediment load from the Hanjiang River;
S F is the amount of sediment depositing in middle and lower reaches in the fluvial processes, which may
be positive (sedimentation) or negative (erosion); S T is the amount of sediment depositing in Tongting
Lake; S E is the annual sediment load at Datong, which represents the sediment load entering the estuary;
S c 1 and S c 2 are the minimum incoming sediment load for initiation of sedimentation in the middle and
lower Yangtze River and Tongting Lake, respectively; and k 1 and k 2 are dimensionless coefficients. Statistical

SkSS ( )

T 2 Y c 2