Abstract
Accurate and reliable estimates of sediment yields from a watershed and identification of unstable stream reaches due to sediment-related disaster are crucial for watershed management, disaster prevention, and hazard mitigation purposes. In this study, we added hydrodynamic and sediment transport modules in a recently developed model to estimate sediment yields and identify the unstable stream reaches in a large-scale watershed (> 100km2). The calibrated and verified models can well reproduce the flow discharge and sediment discharge at the study site, the Shihmen Reservoir Watershed in Taiwan, during several typhoon events. For the scenario applications, the results revealed that the contribution (> 96%) of landslides on sediment supply is much more significant than compared to soil erosion (< 4%). The sediment contribution from the upstream of the hydrological station-Yufeng is approximately 36–55% of the total sediment supply for the rainfall events of 25, 50, 100, and 200 years return period. It also indicates that 22–52% of sediment still remain at foot of the slope and the streams, which become a potential source for sediment hazards in the future. Combining with the bed erosion and deposition depths, flow-induced shear stress from the SRH-2D model, and probability of slope failure within 250 m of stream reaches, the relatively stability of stream reaches can be identified. The results could provide the water resource authorities for reference to take precautionary measures in advance on the stream reaches with high-degree instability.
Highlights
In tropical regions such as Taiwan, high intensity rainfall events from typhoons or plum rains often generate large amounts of sediments eroded from the upstream watershed [1]
Since sediment yield from a watershed is involved with numerous parameters such as local topography, soil, lithology, meteorological conditions, vegetation cover, land use, watershed morphology, and flow hydraulics [4,5], it is very complicated and highly variable in both time and hydromorphological location of watersheds
Sediment yield is estimated based upon the relationship between the suspended sediment concentration and flow discharge established at hydrological stations
Summary
In tropical regions such as Taiwan, high intensity rainfall events from typhoons or plum rains often generate large amounts of sediments eroded from the upstream watershed [1]. These sediments are brought to the downstream reservoir areas, and the decrease of flow velocity causes sediment deposit, which would reduce the reservoir capacity and shorten the lifespan of reservoirs [2,3]. Three approaches are commonly used to estimate the sediment yield, which are field measurements, empirical-statistical models, and physically-based soil erosion-deposition models [6].
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