Flood design for the Tully Alliance Project.

The Tully Alliance Project delivered a 15.5 km National Highway realignment of the Bruce Highway across the combined Tully and Murray Rivers flood plain in north Queensland. This flood plain is located in one of the wettest regions in Australia, with an annual average rainfall throughout the catchment in excess of 4 m. In this area, the previous Bruce Highway could be inundated several times a year for extended periods and this had a significant impact on the movement of freight, tourists and local residents. There were long stretches of the highway that were cut regularly by floodwaters. As well as the low flood immunity, there were safety concerns with the highway formation across the floodplain being essentially a two-lane embankment with no shoulder or stopping lanes. While a high standard of flood immunity was desirable and needed to meet the Department of Main Roads flood immunity standards, the large flood flows experienced on this floodplain meant that a compromise was required. The main reason for this was the high cost associated with the required upgrading works. In addition, raising the highway significantly would cause severe impacts on flood levels for properties located on the flood plain, which was considered unacceptable. Adopted design criteria for the project were therefore related to the time of closure and the minimizing impacts on surrounding land. This paper details the hydraulic analysis undertaken throughout the various phases of the project, and discusses the critical role that hydraulic modelling played in the development of the final vertical and horizontal alignment of the upgraded highway. In addition it discusses the role the community and other stakeholder's played in validating the results of the hydraulic model, and how the flood model was able to assist the community in understanding and accepting the impacts of the proposed upgrade. The final outcomes of the hydraulic investigation are presented, including how the upgraded highway performs against the adopted design criteria. [ABSTRACT FROM AUTHOR]