Weirs continue to flow through drought and fires

However, cattle producer, Martin Royds, Jillamatong, still has more than 20,000 litres of water a day flowing from the weir system he built in 2007.

The weirs have proved invaluable to firefighters during the recent bushfires in the area, which burnt 30 per cent of Mr Royds' property.

"We've had the helicopters sucking out of these weirs all through the fires, at one stage they were taking from them every 40 seconds," Mr Royds said.

The weirs have also been offered as a short-term source of water for the nearby town of Braidwood if needed, with the Shoalhaven River drying up rapidly and its water quality possibly affected by the fires.

"After these fires we're going to have a massive amount of toxins coming out of the burnt forests, the Shoalhaven River's going to be undrinkable for some time," Mr Royds said.

The weirs' ability to stay full and fresh may seem like magic in the middle of a drought, but Mr Royds said it all came down to natural sequence farming and regenerative agriculture.

Mr Royds has been practicing regenerative agriculture for decades, having studied water hydrology and plant dynamics.

In 2005 he met landscape natural sequence pioneer, Peter Andrews, who showed him how his erosion gully was once a chain of ponds.

"The gully was four metres deep and it drained all the water, if we got a big rain event the water ran off into the gully and out to sea very quickly," Mr Royds said.

"Peter taught me how to work with plants and small earthworks to restore the natural landscape function."

Mr Royds said the weirs they helped build slowed the water and allowed it to seep into the surrounding soil, like a sponge.

"I have 34 dams, they're pretty much all dry, two have just a puddle of water in them," he said.

"But these weirs are still full because they're slowing the water down.

"What would have gone out to sea two or three years ago is still flowing out of my system."

As well as saving the flow of water, Mr Royds said compared to farm dams, far less water evaporated from the weirs.

"There are four things that impact evaporation rates, temperature, humidity, wind and surface area," he said.

He said they had measured the temperature of their dams and found the water was 15 degrees at deeper levels and 28 degrees on the surface, in the weirs the temperature was 18 degrees the whole way through.

"If we can have it 10 degrees cooler than a farm dam on the same day, you have exponentially less evaporation," he said.

He said growing reeds in the weirs increased the humidity levels, while planting trees around them reduced wind, both helping to decrease evaporation, even with evapotranspiration from the plants.

But it was surface area, Mr Royds said, that played the biggest role.

"In a pond of water if you have ripples on it you're doubling the water surface, with the water lillies there's no ripples," he said.

Mr Boyds said the weirs were also able to filter the water passing through, keeping it clean.

"The reed beds in the system, catch and filter the water," he said.

"We measured the phosphorous coming in at 12 parts per million and when we measured it going out it was at four parts per million, so we've been able to strip phosphorous, a pollutant in the waterways, out of [the water].

"That's a huge benefit, if you've got clean water you get a 12 per cent increase in productivity of your cattle straight off the bat."

The weirs contrast to the nearby Shoalhaven River, which Mr Royds said stopped flowing more than a month ago.

"The weirs filled up in a 200-millimetre rain event in mid-winter of 2007, the Shoalhaven River flooded then and it all went over Tallowa Dam and out to sea, 455 megalitres of water went over the dam wall," Mr Royds said.

"By 2009 the Shoalhaven had stopped flowing because they ran dozers down the Shoalhaven River in 1973 and turned it into a drain."

But it's not only the weirs that are part of Mr Royds' regenerative agricultural project, he has also been able to sequester large amounts of carbon into his soil, so much so that the soil itself burnt when the bushfire came through.

"We had the soil alight, literally," Mr Royds said.