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 | ||
= | Channel width | |
= | Stable channel width | |
= | Equilibrium water depth under the first channel-forming discharge | |
= | Equilibrium water depth under the second channel-forming discharge | |
= | Water surface elevation under the first channel-forming discharge when the reservoir channel is in equilibrium | |
= | Water surface elevation under the second channel-forming discharge when the reservoir cross-section in equilibrium | |
= | Flood control water level or water level for sediment discharge | |
= | Normal water level | |
= | Original river bed slope | |
= | Equilibrium slope of longitudinal profile | |
= | Equilibrium slope when the channel cross-section of reservoir is in equilibrium | |
= | Distance between the upstream end of sediment deposition and the dam | |
= | Distance from the dam to the intersection between the normal water level Hn and the natural river bed | |
= | Distance from the dam and the intersection between H1(x) and the normal water level Hn | |
= | Distance from the dam and the intersection between and the normal water level Hn | |
= | Distance from the dam to the intersection between the normal water level and | |
= | Manning’s roughness coefficient | |
= | First channel-forming discharge | |
= | Second channel-forming discharge | |
Qm | = | Minimum flow discharge in the sediment discharge period |
QM | = | Maximum flow discharge in the sediment discharge period |
= | Concentration of suspended load | |
= | Average sediment concentration, in the sediment discharge period | |
T | = | Effective sediment discharge period |
= | Conservation storage | |
= | Sediment quantity discharged during the effective sediment discharge period | |
= | Annual average quantity of sediment inflow | |
= | Quantity of sediment inflow in the sediment discharge period | |
= | Original bed surface | |
= | Bed surface when the reservoir channel is in equilibrium | |
= | Bed surface when the reservoir cross-section is in equilibrium | |
= | Settling velocity of suspended load | |
= | River facies coefficient | |
= | Sediment deposition percentage | |
= | Maximum difference between bed level and | |
= | Maximum difference between water level and | |
= | Maximum difference between and (or ) | |
= | Maximum difference between and |