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 |
| = | 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 |
| = | Maximum difference between water level |
| = | Maximum difference between |
| = | Maximum difference between |