Protecting the future of our great floodplains
More than 16 years of monitoring has revealed the benefits of water for the environment across the Gunbower Forest floodplain.
Since 2005, the North Central Catchment Management Authority (CMA) has been supplementing natural flooding with targeted water for the environment programs.
Between 2005 and 2012 water delivery focused on the large permanent and semi-permanent wetlands including Reedy Lagoon. Since the construction of Hipwell Road weir and channel, water has been delivered to about 20 per cent of the forest floodplain twice, in 2014 and 2018, and a smaller one in 2016.
The larger waterings target the middle and lower parts of the floodplain that would have naturally flooded more often, and for longer, before European occupation. These areas include both wetlands and big stands of river red gums.
Botanist Kate Bennetts said she had been monitoring Gunbower’s vegetation for the past 16 years of water for the environment programs, and the results are positive.
“One of the indicators we measure is the condition of tree canopies. If a tree has foliage over at least half of its branches, its canopy is scored as in ‘healthy’ condition,” she said.
“At the river red gum monitoring sites that did not flood between 2005 and 2020, less than half of the trees were in ‘healthy’ condition. These trees appear very drought stressed.
“At the river red gum sites that naturally flooded over this period, the trees were in slightly better condition with almost 60 per cent assessed as ‘healthy’.
“However, the trees in the best condition and which improved the most over the monitoring period were in the river red gum sites that were both naturally flooded and delivered water for the environment. 75 per cent of trees in these more regularly flooded sites were considered ‘healthy’.”
“But, like large areas of south-eastern Australia, the floodplain has suffered from lack of rain both recently and during the Millennium Drought.”
Ms Bennetts said the floodplain understorey flora also responded positively to water for the environment.
“There is a flush of growth with the water, followed by a drying phase where many plants wither back to their root stock and/or seed bank, only to emerge again the next time it floods,” she said.
“Furthermore, we recorded more aquatic plants in the wetlands after delivered water for the environment than after natural flooding.
“Floodplains and wetlands are very dynamic ecosystems and can look very different in the different stages of the hydrological cycle.
“Reinstating small to moderate sized watering events to parts of the floodplain is an important part of maintaining the ecosystems, but the monitoring results suggest that there are many factors, other than flooding, that affect the health of the forest.
“We need to remember the Gunbower floodplain is a modified environment, with 130 years of logging, levee, channel and road construction, weeds, pests and recreation, all which have, and continue to, alter the vegetation.
“Monitoring the vegetation over the past 16 years has also highlighted the negative effect of many years of low rainfall. Drought crosses all land boundaries.”
North Central CMA Program Delivery Executive Manager Rachel Murphy said restoring the floodplains and helping them cope with a changing climate takes time.
“Recovering from more than a century of regulation and the impact of a changing climate is not going to happen overnight,” she said.
“While crops can grow in a few months, it takes a long time to revive a whole ecosystem. Floodplains like Gunbower don’t get as much water as they used to, even in wet years, and floods don’t last as long as they once did.
“We all work within a regulated, heavily modified system and delivering water for the environment is all about working within that system to create as much benefit as possible, with a limited amount of water.
“There aren’t many places like the Gunbower floodplain left. It’s a special place for lots of reasons, and we need to keep protecting it to ensure future generations have the same opportunities to enjoy it as we do. That’s why we do what we do.”
The Gunbower Island water for the environment project is delivered by the North Central CMA in partnership with Goulburn-Murray Water, Murray-Darling Basin Authority, the Commonwealth Environmental Water Office, the Victorian Environmental Water Holder, DELWP and Parks Victoria.
It is part of The Living Murray program, a joint initiative of the New South Wales, Victorian, South Australian, Australian Capital Territory and the Commonwealth governments, coordinated by the MDBA.