FOR water birds and freshwater fish, the periodic flooding of the Powlett estuary is a time of full and plenty. For neighbouring farmers it’s a time of some anxiety.
West Gippsland Catchment Management Authority CEO Martin Fuller said the authority had been contacted by local residents concerned that high water levels in the estuary could cause flooding of private land and roads.
That’s nothing new. For more than a century, farmers on the floodplain have pressed the relevant government department to dredge the mouth of the estuary when it blocks.
But the more scientists have learned about the estuary, the more they have have concluded that artificially opening the mouth can cause major problems . On top of that, it’s not always effective.
Mr Fuller said that given the low flows in the Powlett, and recent ocean conditions, the estuary mouth was likely to reclose if an artificial opening was carried out.
View from the Dalyston footbridge. The closing of the Powlett mouth has created a haven for water birds.
Cattle on an adjoining farmwade through the floodwaters.
The mouth of the Powlett, near the bridge.
“If left alone, the mouth of the Powlett will reopen naturally in time but if water levels in the estuary continue to rise, we may need to excavate sand from the opening.”
The problem is one of timing. If the sandbar is opened under the wrong conditions, oxygen-rich water from the top of the estuary drains into the sea, leaving the oxygen-depleted water at the bottom, which can suffocate fish and other aquatic life.
For the past few weeks, staff and a team of local volunteers from EstuaryWatch have been testing temperature, oxygen levels and turbidity at selected sites along the estuary.
Last Tuesday, dissolved oxygen levels, which sustain life in the estuary water column, were just below 80 per cent near the surface and above 30 per cent near the bottom. River inflows were at just under 40 megalitres a day and water levels in the estuary had increased to just over two metres.
At that depth, water is extending further into the fringing saltmarsh areas that haven’t received saltwater in quite some time. The filling of the floodplain is essential for the breeding and migration of several species of freshwater fish.
A report prepared for the CMA in 2008 concluded that the periodic closing of the mouth of the Powlett was essential to the health of the estuary and floodplain and the species of plants and fishes living there. It recommended an opening once a year, if necessary, during late winter or early spring.
Mr Fuller said any decision to intervene had to take in many factors. “The Powlett River and its estuary are well loved by the coastal community and the health of the river is extremely important.”
Meanwhile, for bird watchers, it’s a wonderful time to visit the estuary and catch the action in the waterholes. The Dalyston bridge is an ideal starting point, with a new walk along a recently fenced off and replanted stretch of the river.
Visit EstuaryWatch for more information and monitoring data from the Powlett River Estuary.
Powlett River Improvement: Opening the mouth and snagging the stream: Powlett Express, September 24, 1915