Destructive flooding induced by broken embankments along Linbian Creek, Taiwan, during Typhoon Morakot

In 2009, Typhoon Morakot made landfall in central Taiwan causing significant damage to property on the island. The Linbian Creek Basin, located in southern Taiwan, which suffered from destructive flooding, was selected as study site. Observations show that high tides downstream obstructed water flow from the Linbian Creek so that it could not be flushed out. The overflow continued to grow because of the accumulation of heavy rainfall in the upper parts of the watershed. In the end, three typical sections of the levee, at (1) Zhuzaijiao, (2) Jiadong, and (3) the Railway Bridge, sustained damage. This overflow from the Linbian Creek resulted in the occurrence of destructive inland typhoon induced flooding. This paper probes into the possible reasons for such extensive flooding along the Linbian Creek. For describing the extremely chaotic flow conditions the writers developed a decoupled model that links three models. Generate waves, wave-induced setups, and storm surges used as a downstream boundary condition in the hydrological model for simulating surface inundation. Numerical results reveal that two key factors caused the flood damage, as follows: (1) the spring tide caused by the storm surge blocked the floodwater from emptying downstream and resulted in a rapid rise of the water level, and (2) scouring and liquefaction at the foot of the creek bank by the discharge. Both lead to broken embankments and water overflowing across the banks at three typical locations. The rapid increase in water from the tributaries and the chaotic water flow inside the channels were construed to be major reasons causing the embankments to collapse.