News
Botanist reveals benefits of ‘environmental water’ across Gunbower floodplain
A BOTANIST has revealed the benefits of environmental water across the Gunbower Forest floodplain after more than 16 years of monitoring.
Hold tight - we’re checking permissions before loading more content
But it is a view disputed by Central Murray Environmental Floodplain Group member Geoff Wakeman, who says environmental water has only been introduced into the floodplain in the past few years.
Since 2005, the North Central Catchment Management Authority 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 Rd 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 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 were 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. A total of 75 per cent of trees in these more regularly flooded sites were considered healthy.”
{image:865126204}
“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.”
Mr Wakeman, who is a geologist, said the Hume Weir was completed in 1936 and water leaving the weir had been regulated ever since.
“Hence, for about 80 years, the vegetation has remained, and survived, in the forest without the need for ‘environmental water’," he said.
Mr Wakeman said the river red gum was the most widely distributed eucalyptus species in Australia growing along watercourses throughout the country, and survived in areas of little rainfall where flooding could be many years apart.
“Leaf shedding is not a sign of an unhealthy tree but is a method of reducing water demand by reducing leaf area. It also reduces heat load under dry conditions when transpiration is reduced,” he said.
“Thus a tree that may look stressed is not necessarily struggling, but merely adapting to suit the current climatic conditions that it may be experiencing. With 2005 being in the middle of the Millennium Drought you would expect the trees to appear drought-stressed, with natural recovery occurring during the 2010-11 floods.”
{image:865125914}
NCCMA program delivery executive manager Rachel Murphy said restoring the floodplains and helping them cope with a changing climate took 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.
“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 NCCMA in partnership with Goulburn-Murray Water, Murray-Darling Basin Authority, the Commonwealth Environmental Water Office, Victorian Environmental Water Holder, DELWP and Parks Victoria.
It is part of The Living Murray program, a joint initiative of the NSW, Victorian, South Australian, ACT and Commonwealth governments, co-ordinated by the MDBA.