Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 380

The equilibrium sedimentation volume V e is proportional to the enhancement of Tongguan's Elevation
' Z t, , which is given by ' Z t Z t - 323.5 , in which Z t is Tongguan's Elevation at time t and 323.5 m is the
Tongguan's Elevation before the dam. Simply the equilibrium sedimentation volume can be imagined to
have a shape like a cone, then it may be assumed
V e A ' Z t /2 (6.5)
In which A is a representative area of riverbed and floodplain on which sedimentation occurs. Substituting
equation (6.5) into (6.4) yields,

ª

t

º

1

Kt

³

Kt

V K e ' Zt e d ' Z (6.6)

« » t t

2

¬ ¼

0

In which t is the time from 1960, when Sanmenxia Dam begin to fill and the Tongguan's Elevation
began to rise. The parameters in the equation are determined from data as A 5.30*10 8 (m 2 )and K 0.15/ yr.
Figure 6.49 shows the calculation result of the sedimentation volume (solid curve) in comparison with
the real sedimentation volume (pyramids). The dashed curve in the figure is the calculation result with the
value of ' Z t remaining unchanged at 5 m ( ' Z t, 328.5 - 323.5 5), which shows that the equilibrium
sedimentation volume is around 1.3 billion m 3 .
As shown in Fig. 6.49 the model agrees well with the data of sedimentation, which proves that for a
given Z t, there is indeed an equilibrium sedimentation volume. If the increment in Tongguan's Elevation
remains unchanged the sedimentation of the lower Weihe River may reach equilibrium in about 25 years.
At present the sedimentation of the lower Weihe River is approaching to the equilibrium volume and
there will be no great volume of accumulated sedimentation if Tongguan's Elevation stops rising.
Nevertheless, the equilibrium sedimentation volume is dynamic and increases with rising lower boundary.
If Tongguan's Elevation continues to rise the equilibrium sedimentation volume will be greater than 1.3
billion m 3 and longer time is needed to reach the equilibrium (Wang and Li, 2003).

Fig. 6.49 Calculated cumulative sedimentation volume with Eq. (4) (solid curve) in comparison with the real
sedimentation volume (pyramids). The dashed curve in the figure is the calculation result with the value of ' Z t
remaining unchanged at 5 m

6.5.5 Changed River Patterns
Sanmenxia Dam not only caused retrogressive sedimentation and erosion in the lower Weihe River, but
also changed the river patterns. Before the reservoir began to be used, the lower Weihe River was a
meandering river, with a value of sinuosity of about 1.65, in which sinuosity is defined as the ratio of the