Bridge Blockage and Overbank Flow Simulations Using HEC–RAS in the Keelung River during the 2001 Nari Typhoon

On September 16, 2001, Typhoon Nari resulted in severe flooding in the Keelung River basin. More than 1,000 shipping containers were swept by the rising water from the floodplain into the river, blocking 14 bridges. A severe overbank flow due to the blockage occurred at the Ba-Tu Railway Bridge. The overbank flow then passed through a railway tunnel and inundated Keelung City, resulting in significant damage. The objective of this study was to determine the influence of the bridge blockage and the Ba-Tu overbank flow on the water stages in the Keelung River during Typhoon Nari. The floating-pier-debris module and the lateral-weir module in the Hydrologic Engineering Center-River Analysis System (HEC-RAS) unsteady-flow routing model were applied to investigate water stage variation due to the bridge blockage and overbank flow. The numerical simulation results provided by this study served as an important reference for authorities who needed to clarify the responsibility of the containersʹ owners for the loss of lives and property during this typhoon.