Scrub Creek Road Unexpected Failure

Abstract

Scrub Creek Road crosses the Brisbane River north of the small town of Fulham. The crossing is around 100m long and goes under water multiple times each year. There is an existing concrete Bridge and concrete causeway and an old reinforces concrete box culvert and 4 large concrete pipes at the center of the crossing which believed to be the lowest point in the riverbed some time ago. The Brisbane River is split in two branches just north of Scrub Creek Road due to the natural movement of sediments during wet seasons over the years. During the 2011 -2013 flood events the eastern channel crossing was damaged and replaced by a concrete bridge. The western channel needed some minor works to keep it functional. Over the years the Brisbane River kept dumping sediments on the eastern channel and forced most of the flow through the western channel. The latest flood events in Feb 2022 and May 2022 destroyed a good portion of the concrete causeway. This was unexpected as the focus was on the structural integrity of the culverts and the bridge as they were well overtopped. However, when the water receded Council was very surprised to see more than 10m of the concrete causeway was washed out and as a result a dozen of families who live on the eastern side of the river were completely isolated for many weeks. Council investigated many alternative access routes through unformed roads and private properties, however none of them was considered viable due to the rough terrain and the risks involved. Council was left with no option, but to try to rebuild the broken causeway to reinstate the access for the isolated families. Many challenges were faced including the continuous wet weather, work within the Brisbane River riparian zone and all the associated permits and approval from multiple state agencies and also the availability of contractors and material. Council started discussions with QRA and multiple state departments in relation to the proposed emergent works to reinstate the causeway and to improve the flow under the bridge by shifting some of the sediments from the eastern channel to allow more water to flow under the bridge and to reduce the pressure on the existing old culverts and the concrete causeway. The paper will provide more details on the stages of the project and the risks associated with each stage and also the mitigation measures for each risk. The project is now listed for a potential betterment funding and is currently at design.