I’ve just spent the last few days in Townsville for the 7th Australian Stream Management Conference – ‘Catchment to Coast’
. The conference kicked off with two very different keynote speakers. The leader of Katter's Australian Party, Bob Katter MP, gave us his views on 21st Century Australia, and the Manager of Coastal Ecosystems at the Great Barrier Reef Marine Park Authority, Donna-marie Audas, talked about the challenges in managing the Great Barrier Reef.
Donna has been managing a project to develop a landscape scale understanding of the Great Barrier Reef catchment and its role in the health and resilience of the Great Barrier Reef. It was really interesting to hear just how complex the system is with 35 river basins and 14 coastal ecosystems
that are important to the function of the Reef: coral reefs, lagoon floor, islands, open water, seagrasses, coastline, estuaries, freshwater wetlands, forested floodplain, heath and shrublands, grass and sedgelands, woodlands, forests and rainforests. Many of these ecosystems have been (and continue to be) altered and degraded. The system is extremely complex, with different issues and solutions in each of the river basins. The ongoing protection of the Great Barrier Reef will be a big challenge for communities and natural resource managers.
There were too many interesting papers presented to mention (they can be accessed from the River Basin Management Society
website if you’re a member). A highlight was hearing Dan Borg from Melbourne Water discuss the success of the Dights Fall fishway on the Yarra River in Melbourne's inner east. Melbourne Water’s monitoring is indicating the fishway is passing the full suite of targeted species and size classes, and there was some great footage of all the fish trapped during the monitoring! Alluvium had a small role in the early stages of the fishway design and it was great to see it has gone on to be successfully implemented by Melbourne Water.
Another highlight was hearing Tony Ladson discuss the permeable pile field groynes that John Tilleard designed on the Mekong River in Vietnam 12 years ago. Pile fields are an erosion control technique consisting of rows of vertical piles in the river that slow the flow velocity and reduce rates of erosion. We design pile fields across eastern Australia to reduce rates of bank erosion, typically using 6 m long piles made from Australian hardwoods, but the Mekong design was on a completely different scale!
Active meander migration in the Mekong Delta was occurring at a rate of over 20 m/year and threatened a $100 m bridge built by AusAID. The river at the bridge is approximately 25 m deep and a 40 m deep scour hole associated with the meander threatened the bridge if meander migration continued. A pile field arrangement which consisted of twelve groynes, each 100 m long, was designed to reduce bank erosion. The concrete piles were up to 20 m long and can’t be seen from the river as their tops sit 15 m below the water level. Ten years on there are no signs of active erosion, and the bank seems to have stabilised in its 2002 location which is a great outcome. Here’s a blog on the works
by my former Alluvium colleague Simon Tilleard.
Mekong Delta from space. Image from Wikipedia.
Overall it was an interesting few days, well done to all those involved in organising it.