Environmental Engineering Reference
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length of the channel to the length of the river valley. The closure of the dam reduced the sinuosity to
1.06 in 1968, as shown in Fig. 6.50a. Very quick sedimentation in this period buried the meandering
channel. In the meantime a straight channel developed which was affected mainly by the reservoir
operation. In the period from 1970 to 1975 the Weihe River experienced erosion and the channel developed
gradually from straight to meandering. The sinuosity had gradually increased to 1.2. In the following
period more and more meanders have developed and the lower Weihe River has been developing toward
meandering with a sinuosity about 1.3.
Moreover, the river channel has become quite unstable since the closure of the dam. Figure 6.50b
shows the migration distances of the stream channel measured at cross-sections WY5-35 during the first
ascending and descending periods of Tongguan's Elevation. The migration distance was up to 1.8 km at the
cross-sections near Huaxian (WY11). The dam had less effect in the reaches further upstream and the
migration distance was less than 1 km at cross-sections WY18-35.
Fig. 6.50 (a) Variation of sinuosity of the lower Weihe River; (b) Migration distances of the stream channel measured
at cross-sections WY5-WY35 during the first ascending and first descending periods of Tongguan's Elevation
6.5.6 Erosion and Resiltation Below Sanmenxia Dam
Sanmenxia Reservoir has trapped about 7.1 billion m 3 of sediment in 45 years, including the sedimentation
volume in the Weihe River. The sediment load and runoff in the downstream reaches was then greatly
reduced, especially in the first 4 years, which induced a complex morphological process downstream of
the dam. The water and sediment released from Sanmenxia Dam varied with the operation modes of the
reservoir. Consequently, erosion and resiltation occurred in the reaches downstream from the dam. The
process of bed erosion and resiltation was very fast because the sediment load was high and the bed
material was erodible. The erosion and resiltation occurred mainly in the reach about 180-600 km
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