Flood Defense and Water/Sediment Management—With Particular Reference to The Yellow River - River Dynamics and Integrated River Management - page 373

restrictions. The reservoir was operated at a low storage level throughout the year, detaining floods only
during flood seasons and sluicing sediment with the largest possible discharges.
(3) Controlled release. The mode has been used since November 1974, to store relatively clear water
in non-flood seasons (November-June) and dispose of muddy water in flood seasons (July-October). In
this period, the reservoir has been operated at a high water level in non-flood seasons, and at a low
storage level during flood seasons, and all the outlets were to be opened in times of flood peaks to sluice
the sediment as much as possible.

Fig. 6.42 Variation of average pool level of the Sanmenxia Reservoir in different time periods

Sedimentation in the reservoir is different corresponding to different operational modes and the outlet
discharge capacities. Table 6.8 presents a summary of the amount of sediment deposited in the reservoir
from Tongguan to the dam during the periods of different operation modes. The mean annual deposition
volumes in the reservoir area are 620.38 u 10 6 , -102.51 u 10 6 , and 12.57u10 6 m 3 during the periods of
storage, flood detention, and controlled release, respectively. Because the reservoir was operated at a low
storage level and the discharge capacity was enlarged in the period of flood detention, the reservoir
sediment was changed from accumulating to scouring. In the period of controlled release, deposition
occurred during non-flood seasons while scouring occurred in flood seasons.
Figure 6.43a shows the accumulated volume of sediment deposition in different reaches in the reservoir
area and Fig. 6.43b shows the variation of reservoir storage capacity. Within the range of operation levels

Table 6.8 Summary of sedimentation during different operation periods at Sanmenxia Reservoir

Mean Annual Deposition (10 6 m 3 ) Maximum

Discharge
at 315 m
(m 3 /s)

Average
Annual
Runoff
(10 9 m 3 )

Average
Annual
Sediment
(10 9 tons)

Time
period

Mode of
Operation

Non-flood season
(Nov.-June)

Flood season
(July-Oct.)

Year

9/1960
-10/1964

Storage 3,080 46.2 1.34 70.11 550.27 620.38

11/1964
-10/1973

Flood
Detention

6,100 38.2 1.44 -63.61 -38.90 -102.51

11/1973
-10/2001

Controlled
Release

10,000 31.6 0.86 129.02 -116.45 12.57