In June 2019, fish passage was rehabilitated at the Forbes Road causeway in the middle reaches of the O’Connell River, north of Mackay. The causeway had a pre-existing fishway, which unfortunately was significantly damaged during 1 in 500-year stream flows caused by tropical cyclone Debbie. As such, repairs to the damaged fishway were funded by the Australian Federal Government’s disaster recovery funding, via Mackay Regional Council who engaged Catchment Solutions to undertake the repair works.
The repaired fishway is comprised of 12 ridges and pools, with 75mm drops between each pool to ascend the overall 800mm causeway barrier height. Fishway ridges are spaced 2m apart to allow for maximum flow dissipation. The fishway functions through fish approaching from downstream and using their burst speed to ascend the fishway ridge slots, before using turbulent-free resting zones in the pools to regain their energy before ascending the next ridge. Upon reaching the top of the fishway, fish can pass under the causeway barrier through a single box culvert installed within the causeway deck. Importantly, the fishway maintains consistent flow through each ridge slot, and features deep pools which dissipate this flow energy. These features are critical in ensuring the young-of-year recruits of diadromous species such as tarpon, barramundi, mangrove jack and jungle perch which are poor swimmers, are able to negotiate the fishway and reach upstream habitats.
Figure 1. Left; Commencement of fishway repairs, with first wall rocks in place and right; showing excavator working at bottom of fishway with pumps removing water from site.
Figure 2. Left; Fishway completed prior to concreting and right; standing at bottom of fishway facing upstream showing completed concreting of both walls and all fishway ridges with fibre-reinforced concrete.
Figure 3. Left; Standing on causeway facing downstream showing fishway after concreting and right; standing on causeway showing fishway during its first flow after being opened following construction.
Figure 4. Forbes Road fishway at the completion of repair works, restoring aquatic connectivity past the causeway barrier for migratory Australian fish species.