Mobile Bed Simulations on River Scouring and Deposition - A Case Study of Dajia River, Taiwan

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Dong-Sin Shih, Yuan-Ya Liao

Tuesday 30 june 2015

17:51 - 17:54h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling, Poster pitches

Parallel session: Poster pitches: 7A. Sediment - Erosion

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This research is focused on the process of local scouring and its deposition of river bed during the flash flood in Dajia River, Taiwan. The Dajia River is selected to study since it is labeled as one of most severe river in Taiwan due to its varied morphology. The river has not only steep slope, but fragile bed with heterogeneous gravels along the river. In order to better understand its scoring process, we combined mobile bed simulation model and local field investigations to study its temporal variability of river bed during flood. We first established a mobile river modeling system and calibrate simulations via experimental data. The system was tested on the circumstances of river scouring and deposition. It revealed a reasonable result on model calibration. And our simulation system is further modeled using extreme typhoon events. Two extreme cases were implemented to evaluate model performance with checking observed river stages and bed variations. The results revealed that our modeling system can fairly match the pattern of selected flash flood. This established mobile bed system was then applied to simulate the circumstances of different return periods of discharges and the scenarios of remove dams on channel. It shows that the local scours on some cross sections are extreme deep. As compared the modeling results to the reality, it implies that the selected sediment formula and river deposition mechanism may be further modified. In order to address above problem, we propose a method to combine the mobile bed simulations and field measurements to reconstruct the temporal variability of local scoring and bed deposition. The simulation shows that proposed approach can mostly catch changeable river bed on Dajia River for extreme event.