Vulnerability of floodways under extreme flood events

Floodways are commonly used in rural road networks due to the economic and environmental benefits offered as a low-cost and practical road crossing in flood-prone areas. They are designed with provision for submergence so that water flows over with minimum impediment to flow, at a probability given design flood. The floodway design process is traditionally governed by hydraulic aspects rather than structural aspects. Hydrological condition, availability of material, and familiarity of construction techniques are significant when selecting the floodway type. Nevertheless, extreme conditions can cause significant damage to floodways, as was evident from the 2011 and 2013 Queensland flood events, during which 58% of floodways in the Lockyer Valley Regional Council (LVRC) area in Queensland, Australia, which is the case study area of this paper, were damaged, causing huge economic lost at council and national level. This created a new track in research and development activities to assess vulnerability and to find methods for improving the resilience of floodways during extreme flood events. In line with this, the present study evaluates local design guidelines and damaged floodways to assess failure modes and severity of damage using a damage index (DI) method