Modelling the effects of typhoons on morphological changes in the Estuary of Beinan, Taiwan

- This study used measured and simulated results to analyze the effect of typhoon.
- The effects of the waves, tides, wave induced currents, and suspended load of the river to the changes of the bathymetry were all taken into consideration.
- Typhoons can cause either accretion or erosion at the river mouth, depending on the balance between river discharges and wave action.

On average, Taiwan is subjected to three or four typhoon invasions each year. As a typhoon approaches, strong ocean waves from the sea, which are accompanied by flash floods on land, can considerably change the morphology of estuaries. Thus, knowing the effect of typhoons is important for coastal management. This study uses simulations and field surveys to analyze the processes of sediment transport near the Beinan Estuary in southeastern Taiwan. A model that is based on Eulerian and Lagrangian methods is used to simulate sediment transport from fluvial flows, waves, and currents. Typhoons of various intensities, different types of fluvial hydrographs, and seasonal effects are used to study their effects on the bathymetry. The relationships among the fluvial sediments, the wave loads, and the evolution of the estuary are derived from the results. The results indicate that the morphology of the Beinan Estuary is governed by typhoon events and that the process of erosion, transport, and deposition of sediment are short. The amount of fluvial sediments that is required to cause changes in the estuary is determined based on these results, and this estimate can be used for erosion protection in the future.