Abstract
Sedimentation limits the benefits of storage reservoirs, especially in areas with higher sediment yields, such as Agongdian Reservoir in southern Taiwan. Although drawdown flushing is a known strategy that releases large amounts of fine sediment into a downstream channel, there is limited information on the long-term monitoring and multiple metrics being used to evaluate flushing efficiency. The objectives of this study were three-fold: (1) to continue collecting valuable long-term observed data, since Agongdian Reservoir is one of the few reservoirs currently conducting sediment flushing operations; (2) to evaluate and identify the hydrological parameters that are highly related to the flushing efficiency; (3) to execute numerical simulations of different reservoir flushing scenarios at multiple water levels to discuss potential strategies to improve the flushing efficiency. The findings of this study revealed that long-term monitoring data was valuable for identifying factors highly related to the flushing efficiency, which included the initial water level; average water level; average velocity. Based on simulations, compartmentalizing the reservoir is a proposed strategy that has demonstrated high levels of improvement in terms of the flushing efficiency, depending on particular scenarios involving partition desilting, empty flushing, or a combination of both. Recommendations to increase the flushing efficiency include lowering the initial water level, creating a narrower gorge-like geometry by partitioning, and further considering to modify the operation rules.
Highlights
Reservoirs play a vital role in providing a water supply for human usage, which includes irrigation practices
From 2010 to 2015, findings showed that 94% of the observed rainfall occurred in the rainy season (March to September), with 77% of the observed rainfall primarily occurring during the flushing period (June to September (Figure 3a))
While Typhoon Fanapi is a prime example illustrating an obvious shift in earlier sediment flushing, the three other typhoon events selected in this study had a more subtle overall shift
Summary
Reservoirs play a vital role in providing a water supply for human usage, which includes irrigation practices. Sedimentation limits the benefits of storage reservoirs and increases the risks of an aging infrastructure, especially for areas with a higher sediment yield. With such impacts becoming increasingly widespread, reservoir managers should implement practices to best sustain the storage capacity of a reservoir. Sustainable sediment management can be accomplished by a suite of strategies [1,2,3,4], all of which are aimed at maintaining the reservoir capacity. Some specific factors to take into consideration include: reservoirs dealing with carryover storage; synchrony with the natural sediment supply; the water demand for each unit of sediment managed; the effectiveness of maintaining the reservoir capacity; the ability to meet the necessary infrastructure and hydraulic conditions. Bypass channels require certain geological conditions at the site
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