Analysis of Factors Affecting the Annual Average Silt Loss Rate of Reservoirs

China is the country with the largest number of reservoirs in the world. According to the “Bulletin of First National Census for Water”, in China there are presently a total of 98,002, for a total reservoir capacity of 932.3×10⁹ m³. Reservoirs play important roles in alleviating flood disasters, ensuring water supply, providing clean energy, and maintaining regional ecological balance. China is also the country with the most serious reservoir siltation in the world, with an annual average silt loss rate in its reservoirs (the annual average siltation of the reservoir / total reservoir capacity) reaching 2.3%. This has seriously affected the function and safety of the reservoirs. Therefore, it is of theoretical significance and practical application value to extend the service life of reservoirs and improve the utilization function efficiency of reservoirs by carrying out research on the factors affecting the annual average silt loss rate of the reservoir, and by proposing the measures to reduce the reservoirs` silt loss.

The annual average silt loss rate of reservoirs is an index reflecting the annual average capacity loss of reservoirs within a certain period. The analysis shows that the annual average silt loss rate of the reservoirs decreases with the increase of the storage-sediment ratio (total storage capacity/annual average volume of sediment entering into reservoirs). The Three Gorges Reservoir has a storage-sediment ratio of 255.0 and annual average silt loss rate of 0.25% during the period of 2003 to 2016; The Xiaolangdi Reservoir has a storage-sediment ratio of 43.1 from 1999 to 2016, which is only 26.9% of that of the Three Gorges Reservoir, and annual average silt loss rate of 1.36%, which is 5.4 times of that of the Three Gorges Reservoir. The annual average silt loss rate of reservoirs is also closely related to the operation mode, reservoir sediment inflow process, and operation stages of reservoirs. Furthermore, comprehensive measures were proposed to reduce the annual average silt loss rate of the reservoir and prolong the service life of the reservoir. These included an increase in the storage-sediment ratio, adoption of favorable sand desilting operation mode for reservoir, and optimization of reservoir sediment inflow process.