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Big rain makes farm's bathroom-sized sinkhole flow

Jemima Burt, Monday September 11, 2017 - 06:06 EST
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Farmer Tony Beck stands next to the sinkhole, where rainwater is flowing into the aquifer. - ABC

Drain skiing, mud fighting and swamping are just some activities rural Australians have invented to ward off cabin fever during wet weather.

But Tony Beck has spent his time during the recent wet weather a bit differently to most.

He has been observing a spontaneous waterfall which began flowing smack bang in the middle of one of his paddocks.

The Becks received almost 150mm of rain during July and August.

Regional geology perfect for sinkholes

The south east of South Australia is also known as the Limestone Coast, for the highly porous rock it sits on.

This is the perfect geology for sinkholes to appear and, in one case, a sinkhole is even thought to have swallowed a horse.

Sinkholes have been known to flow spontaneously during wet weather, like this incident on an urban street.

"The rain water infiltrates down into that limestone and dissolves part of it away and forms these large caves or caverns down there," Mr Beck said.

"Then it eventually silts over, fills up and then thousands of years later or so, in a dry period, the clay that sits above the Bridgewater sandstone will crack open enough to allow water to wash down through the clay and into the aquifer by that route."

This makes the world heritage-listed farm a perfect habitat for all sorts of wildlife.

"In the spring, this will be absolutely teeming with aquatic life. There'll be all sorts of tadpoles, lepidurus and fairy shrimps," the South Australian farmer said.

Sinkholes active again after dry years

"This latest spate of sinkholes that are actually active and running the surface water away has occurred because of the 2007 drought followed by the dry springs of 2014 and 2015 and then a wet winter in 2016," Mr Beck said.

"It's that weather that actually opened up the pathways and actually made them active again."

What is an active sinkhole you ask? Basically a sinkhole with a waterfall.

"It's one that hasn't silted up again. The cave has obviously collapsed, it's opened a pathway. It washes tonnes and tonnes of soil into the caves below," Mr Beck said.

Mr Beck said his sinkhole problems were usually solved by his sheep, which run in circles around them and compact the dirt.

"The sheep run around and around. The lambs love playing in them. They think they're velodromes for hours on end, packing the soil down and resealing them. But that one is too deep for them to actually get into."

At this stage, no houses have been swallowed by the Limestone Coast's unique geological landscape.

But who knows what the future holds …


© ABC 2017

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