It was in 2007, in the depths of the devastating Millennium Drought, that Mark Toohey started digging small ponds along the Bendigo Creek catchment to try to keep the creek bed moist and alive.
“During the drought years, those ponds never dried up. People couldn’t believe it,” the City of Greater Bendigo park ranger recalls.
Re-establishing native frog ponds along waterways helps slow the flow, a measure Toohey and other experts say will be critical for sustaining riparian ecosystems during forecast climate extremes.
The theory could be tested this summer, given the Bureau of Meteorology’s declaration that Australia is now in the grip of an El Nino weather pattern delivering hot, dry conditions.
Frog ponds and their associated native grasses provide habitat for a variety of animals and insects, creating a cooling effect and acting as a natural barrier, keeping water in the creek system for longer, says Toohey.
Slowing the water helps mitigate the major erosion problems that are a legacy of the region’s mining history. The removal of trees, roots, rocks and clay over the years has allowed large volumes of water to rush unimpeded through exposed and vulnerable subsoil.
“When it rains, the rain does not get held in the catchments,” Toohey says.
“It doesn’t get stopped or slowed or held up, it goes really quickly downhill, gravity takes over … and causes more erosion.”
The benefits of this kind of rehabilitation are on show in a project jointly managed by Indigenous corporation Djaara and the City of Greater Bendigo as part of the Reimagining Bendigo Creek scheme.
Named Wanyarram Dhelk, the project has restored a section of the creek to its original state, a chain of ponds of varying depths.
The deeper ponds trap sediment and filter dirty water before it flows into catchments downstream, while the shallower pools oxygenate the water and create animal habitats. Managed and revegetated according to Indigenous land management principles, it is already proved beneficial to biodiversity.
The ponds function as a hybrid system of water distribution, where rainfall is both detained in the larger pools and retained in the soil, to be gradually released over time. The payoff extends well beyond the creek itself.
“When we trap water, we’re holding it in the catchment. That water has a cooling effect upon our city and also has the ability to seep into the soil structure,” Toohey says.
The ponds don’t dry out “because there’s this reservoir of water slowly moving in the silt”.
Slowing flows also prevents flooding in other parts of the river during periods of high rainfall, he says.
“The flooding downstream will be lessened because we’ve got these retention-detention basins higher up in the catchment.”
The re-creation of such pond systems provides a powerful example of “nature-based solutions” to climate extremes, says adaptation expert Associate Professor Robert Faggian of Deakin University
“With climate change, we’ll probably oscillate between El Nino and La Nina quite regularly, that means we’re going to have floods one year, drought the next,” Faggian says, referring to the dry and wet cycles of the El Nino Southern Oscillation.
“At this point in time, it looks like we’ll have longer, more severe droughts and less rainfall, although it’ll fall in bigger dumps,” Faggian says. “There is an opportunity to capture flood water in periods of flood, store it and use it during peaks and troughs.
“The water has a chance to evaporate slowly. Birds and insects can engage with it, and the water can still seep out and into the underground water flow system.”
This is the third story of the ongoing Future Bendigo series, a collaboration between the University of Melbourne’s Centre for Advancing Journalism and the Bendigo Advertiser.
