Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 411

Fig. 7.8 Profile of the Bajiazui Reservoir on the Puhe River showing a wedge shaped deposit (after IRTCES, 1985)
Tapering deposit— A tapering deposit occurs in large reservoirs normally remaining at a high pool
level, it is formed due to the progressive deposition of fine sediment from the flowing water moving
toward the dam.
Uniform deposit— Uniform deposition occurs in narrow reservoirs with frequent water level fluctuation
and a small inflow of fine sediment.
Combined patterns— Fine sediment deposits in the vincinity of the dam and form a wedge and coarse
sediment deposits in the upper most part of the reservoir forming a delta. The Sakuma Reservoir in Japan
exhibits such a complex depositional pattern, as shown in Fig. 7.9.
Fig. 7.9 (a) Complex longitudinal profile of the Sakuma Reservoir in Japan (after 24 years of operation); (b) Grain size
distributions of deposits at different sites in the reservoir (after Okada Tsuyoshi and Baba Kyohei, 1982)
7.2.2 Sedimentation Management Strategies
Various strategies for reservoir sedimentation control have been studied and applied in reservoir
management. Fan and Morris (1992 a and b) summarized the strategies with particular attention to
turbidity currents. Garcia studied turbidity currents with poorly sorted sediment and sediment deposition
in reservoirs (Garcia, 1994). Sediment bypassing is a method used to manage sediment by preventing it
from entering the reservoir. An offstream reservoir can generate benefits in addition to a reduced rate of
storage depletion (Morris et al., 2008). Empty flushing involves the opening of bottom outlets to
completely empty the reservoir and allow stream flow to scour sediment deposits. The scouring of
sediment by flood depends on the permeability, consolidation coefficient and the volume fraction of sand
related to silt (Jacobs et al, 2007).
Wang and Hu (2009) summarized the reservoir sedimentation management strategies applied in China.
Five strategies have been applied for reservoir sedimentation control: 1) Drawdown flushing or pressure