Resilient treatment options for assets adjacent to waterways - Disaster Recovery Works

Abstract

This abstract outline a comprehensive approach to the pavement washouts adjacent to the floodway sections and batter erosions, batter reinstatement works and significant bank scour. During the 2022 rain event, Mt.Sylvia road, Mulgowie road and Murphy’s creek road were significantly affected. As part of the DRFA works, the team at TMR Darling Downs proposed a sustainable solution tailored to the region's specific challenges rather than traditional approach of “like for like” as stipulated under DRFA guidelines. On Mt.Sylvia Road where there were pavement washouts adjacent to the existing concrete floodway, concrete floodway extensions and concrete batters were proposed at various lengths as the best engineered solutions in lieu of unbound granular pavement. TMR engaged a design consultant to develop the design at these floodway sections and QRA funded this project via both REPA and betterment funding to achieve a more resilient design. Two major batter erosion sections were identified within the road reserve where original Blackfellow creek alignment had significantly changed and approaching into existing road. Lockyer Valley Regional council had secured funds to deliver a lager scope of work at these locations under river resilient funding and had engaged a design consultant to develop the design. TMR had a collaborative approach to fund the eligible scope under DRFA funding to achieve a more resilient design and importantly accessible to the community during future rain events. The proposed design is rock fill scour protections on the batter with installation of series of rock groynes as energy dissipation structures. TMR engaged a design consultant to provide design options for the major bank scour section on Mulgowie road at CH10.80. Following on the geotechnical investigation and comprehensive hydraulics studies, the most feasible design is to bench the bank and install rockfill over 90m length and the depth various from 8-10m. The scour depth at this location was up to 9m where Laidley Creek had overtopped the road during 2022 rain events. The Laidley creek is considered as a fish passage and classified as a purple waterway. Hence, it was paramount the balance of the design with the environmental compliance. TMR was able to secure funds as part REPA funding as the best engineered solution by conducting the “Value for Money” exercise for selected design options. Batter scour section of Murphy’s creek road at CH18.5 which rock protection works were fully washed out during the rain events and further scouring on the batter and undermined a section of road. This section was affected during 2011 floods and rock protection works was completed in 2013. It was understood that rock protection was not a viable option and explored options in line with DRFA guidelines for funding eligibility. After engaging the design consultant, the shotcrete option was adopted as the feasible design option to reinstate the batter. The length of the batter is about 200m at various widths range from 4-6m. In conclusion, the design options adopted at these sites will provide resilient product and improve protection to the assets during future events.