Impact of hydrodynamic characteristics and sediment transport mechanisms in reservoir areas and downstream river channels

The long-term sustainability of reservoir water resources depends on preserving storage capacity, making sediment management a critical component of reservoir operations. Shihmen Reservoir in Taiwan has experienced significant sedimentation due to extreme floods triggered by typhoon events, leading to a substantial loss of storage capacity. This study examines management strategies to minimize sediment deposition and restore reservoir capacity. Two key assessment indices, the capacity-inflow ratio and capacity-sediment ratio, are analyzed to evaluate the effectiveness of desilting techniques. Three major desilting projects have been implemented to mitigate sedimentation: a modified power plant penstock and two desilting tunnels. Without proper sediment management, the reservoir’s storage capacity will decline to 33.94 % of its initial capacity over the next 50 years. However, with the planned sediment management measures, up to 70.3% of the original capacity can be preserved, ensuring a sustainable water supply to meet future demands. The study also investigates the downstream impacts of desilting operations using a hydro-morphological model to simulate floodwater levels and riverbed changes. Results indicate long-term desilting operations will lead to downstream river morphology adjustments toward equilibrium. Although sediment concentration increases temporarily during desilting, it gradually decreases along the river. Furthermore, despite some riverbed deposition, the elevation changes do not significantly affect floodwater levels. These findings highlight the necessity of well-planned sediment management strategies to sustain reservoir capacity while minimizing adverse downstream effects, ultimately contributing to long-term water resource sustainability.