Author(s): Fang Yenn Teo; Yuk San Liew; Roger A. Falconer; Bin Liang Lin
Keywords: Urban flooding; Flood hazard; Vehicle blockage at bridge; Hydrodynamic modelling
Abstract: Flooding may cause potential hazard risks to humans and their properties along floodplains. In most urban floodplains, vehicles can possibly be carried downstream by floodwaters into rivers and then build up in front of bridges. The situation can become severe when water impinges on the superstructure of bridges, as these vehicles can block the flow path and strike the actual bridge structure, rather than just the pier or abutment. This may finally causes failure of the bridge under such stress. This paper therefore looks into the consequential impact on flood hazard risks of vehicles blockages at bridges. A numerical model study has been included to simulate the similar conditions in a floodplain, at the township of Segamat, Malaysia. Simulations have been carried out for vehicles blocking in front of bridges with the aim of studying the effects on aspects of the hydrodynamic processes and to establish an understanding of the concepts and conditions of real environments for vehicle blockages occurring at bridges. Through the assessment for different conditions of floodwater flow and bridge setups, the two principal factors of hazard (i. e. the floodwater depth and flow velocity induced by the floodwater at blocked bridges) have been identified. Comparisons of the velocity profiles and water elevations have also been undertaken. The results show that: (i) the obstruction caused by vehicle blockages at bridges have a significant impact on the flow propagation and the hydrodynamic processes along floodplains, (ii) the water surface elevations can be affected for some distance upstream of the obstruction, where a large backwater effect extends far upstream of the obstruction, and (iii) the area at the upstream end of the obstruction becomes more of a hazard than that at the downstream end. The findings propose that the alternative flood alleviation approaches, such as building flood fencing or a retaining wall along the floodplains, may help to prevent flooded vehicles from being flushed into the river and creating a blockage at bridge.