“We cannot underestimate how significant this achievement is. These big pieces of infrastructure are complex projects,” said Queensland Minister of Water Glenn Butcher in a statement. “Rookwood Weir was delivered in an in-river environment and impacted by inundation events throughout construction.”

The weir is the first large water infrastructure project to be built in Australia in more than a decade, and features a 16.2-m-high x 350-m-long mass concrete dam as well as a two-lock fish chamber with castellated crest blocks. It also includes Australia’s first 172-m-long turtle passage. These elements enable aquatic life to more easily move through natural life cycle passages without requiring additional water releases, according to consultant GHD, project design lead.

The weir was delivered through an alliance among GHD; Acciona and McCosker Contracting, for construction services; and Sunwater, a government-owned corporate water provider in Queensland, which provided funding along with the state and federal governments.

It is also the first weir in Australia and New Zealand to be awarded an “excellent” design rating by the Infrastructure Sustainability Council.

The fish lock has two chambers, five attraction slots and four exit panels. This design widened the lock’s operational range, enabling twice as many fish to pass through it compared to a traditional single-chamber lock.
Photos courtesy of GHD

Addressing Challenges

Construction on the project was just getting started when the pandemic hit. Nick Hamilton, GHD senior technical director for dams and hydropower structures, says the project team was able to get around quarantine and flight restrictions by transporting workers on chartered planes and housing them on site. “Because we were in our own little bubble, we could get around those restrictions,” he says.

Additionally, the river where crews were working flooded six times, with one rainy period lasting over the course of several months. Initially, project managers found other work on site that did not require workers to be in the river.

But with each event, the project team grew more efficient in cleaning up after floodwaters receded, so on-site inundation was less of an impediment as the project progressed. Cleanups “went from a couple of weeks down to three or four days,” Hamilton says.

The weir is seen in October 2023, about one month prior to project completion.
Photo courtesy of GHD

Environmental-friendly Features

The alliance team wanted to design the project with carbon and energy savings in mind. With the assistance of an expert technical panel, team members developed a project-specific concrete mix that incorporated a combination of 63% coal ash and 75 mm aggregate to reduce the amount of cement—with its related carbon emissions—that was needed for the 131 cu m of concrete used on the project.

One unique aspect of the project is the turtle ladder—the first passage in Australia to allow safe upstream and downstream movement for turtles across a weir or dam.

The team worked with five years’ worth of data from an ongoing Australian turtle telemetry project to study the behavior and movement patterns of the turtles to be able to design a passageway that would support natural behaviors.

According to the submission, the telemetry project is the largest freshwater turtle movement study of its kind in the world. It involves placing sensors on animals and tracing their patterns using acoustic monitoring.

The Rookwood team looked at data from more than 130 turtles within a 30-km radius of the river to inform the design of the ladder. It included two sloped ramps that are designed not to exceed a 45° angle, as well as resting pools located every 15 m for the turtles.

“We knew they could climb up that kind of angle,” says Tracey Williamson, senior technical director for dams at GHD. “The great thing was, after everything was built, we actually have seen turtles at the top, so all the science did come to fruition at the end.”