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Articles

Study on channel-forming process and a mathematical model for conservation storage for long-term utilized reservoirs

Pages 397-411 | Received 09 Aug 2017, Accepted 21 Jul 2019, Published online: 27 Nov 2019
 

ABSTRACT

It was conventionally believed that a large multi-purpose reservoir would eventually be abandoned because of the sediment deposition caused by the long-term elevation of water level. The concept of the reservoir life was introduced based on this convention. The concept of long-term utilization of reservoirs was first proposed by some Chinese researchers, who also investigated the sedimentation process during the long-term operation of reservoirs and applied the long-term operation strategy in the planning and operation practices for large reservoirs. Based on the general law of reservoir sedimentation, the mechanism of the long-term utilization of reservoirs was discussed in this paper. The channel-forming process for long-term utilized reservoirs was investigated, the first and the second channel-forming discharges were introduced, and the formation of the relative equilibrium longitudinal channel profile and cross-section was analysed. A quantitative relation was derived for the conservation cross section and storage with respect to the sediment discharge period and the control water level. A mathematical model was developed for the long-term utilization of reservoirs. As a case study, this model was applied to the planning of the long-term utilization of the Three Gorges Reservoir.

Acknowledgement

Thanks Dr. Wenkai, Qin for translating this article from Chinese to English.

Notation
B =

Channel width

Bc =

Stable channel width

h1 =

Equilibrium water depth under the first channel-forming discharge

h2 =

Equilibrium water depth under the second channel-forming discharge

H1(x) =

Water surface elevation under the first channel-forming discharge when the reservoir channel is in equilibrium

H2(x) =

Water surface elevation under the second channel-forming discharge when the reservoir cross-section in equilibrium

HF =

Flood control water level or water level for sediment discharge

Hn =

Normal water level

J0 =

Original river bed slope

Jc =

Equilibrium slope of longitudinal profile

J2 =

Equilibrium slope when the channel cross-section of reservoir is in equilibrium

L =

Distance between the upstream end of sediment deposition and the dam

L0 =

Distance from the dam to the intersection between the normal water level Hn and the natural river bed

L1 =

Distance from the dam and the intersection between H1(x) and the normal water level Hn

L2 =

Distance from the dam and the intersection between H2(x) and the normal water level Hn

L4 =

Distance from the dam to the intersection between the normal water level and Z0(x)

n =

Manning’s roughness coefficientQFQn

Q1 =

First channel-forming discharge

Q2 =

Second channel-forming discharge

Qm =

Minimum flow discharge in the sediment discharge period

QM =

Maximum flow discharge in the sediment discharge period

S =

Concentration of suspended load

S¯ =

Average sediment concentration, in the sediment discharge period

T =

Effective sediment discharge period

V1.c =

Conservation storage

Ws =

Sediment quantity discharged during the effective sediment discharge period

Ws.0 =

Annual average quantity of sediment inflow

Ws.1 =

Quantity of sediment inflow in the sediment discharge period

Z0(x) =

Original bed surface

Z1(x) =

Bed surface when the reservoir channel is in equilibrium

Z2(x) =

Bed surface when the reservoir cross-section is in equilibrium

ω =

Settling velocity of suspended load

ξ =

River facies coefficient

λ =

Sediment deposition percentage

δ1.M =

Maximum difference between bed level Z1(x) and Z2(x)

δ2.M =

Maximum difference between water level H1(x) and H2(x)

ΔH0 =

Maximum difference between Hn and H1(x) (or H2(x))

ΔZ0 =

Maximum difference between Z2(x) and Z0(x)

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