Floodway Design Process Revisited

Abstract

Floodways are small road structures that are designed to be overtopped by floodwater during flood events of relatively low average recurrence intervals. Once floodwaters recede, it is expected that the structure will return to normal service providing a vital link within the rural road network. The severity of the 2011 and 2013 flood events in Queensland severely damaged floodways causing a devastating impact on rural communities during the recovery and rehabilitation efforts. From these extreme flood events it was demonstrated that the resilience of these critical road structures is of great significance for the survival, safety and recovery stages of communities. Using Lockyer Valley Regional Council area as a case study, the authors have demonstrated that the majority of structural damage was sustained due to heavy impact loadings caused from boulders and logs being conveyed by floodwaters. Another aspect reviewed was the damage sustained to the floodway apron due to the excessive debris loading, this was of particular concern as concrete aprons are of a significant expense to road authorities to repair and/or replace. As a result of floodways encountering many forces throughout their serviceable life, thorough review and investigation of current design guidelines is required to improve floodway resilience. This paper utilises finite element methods and a detailed parametric analysis to investigate structural vulnerability of a single floodway type and reports the procedure used to develop structural design charts. Finally, the contribution that resulted from the structural analysis is linked with the methodology presented in current floodway design guidelines.