With the majority of Australia’s population living along the coast, the management of coastal groundwater resources is becoming ever more important.
Recent research of groundwater systems at the land–ocean interface has clearly shown the importance of acknowledging the connectivity between onshore and offshore parts of coastal aquifers.
This information is necessary to understand and predict the movement of groundwater and its dissolved solutes across a range of spatial and temporal scales.
Coastal aquifer systems do not terminate at the coastline, and nor is the coastline fixed in time.
Past changes of sea level and coastline migration still have an influence on the groundwater salinity distribution today.
This presentation reviews the current state of the science, and explains the need for more research on the offshore parts of aquifers, which may contain significant volumes of exploitable groundwater.
From ABC
Vast freshwater reserves are trapped beneath the ocean
floor which could sustain future generations as current sources dwindle,
say an international team of scientists.
In this week's issue of
Nature
they estimate 500,000 cubic kilometres of low-salinity water is buried
beneath the seabed on continental shelves around the world, including
off Australia, China, North America and South Africa.
"The volume of this water resource is a hundred times greater than
the amount we've extracted from the Earth's sub-surface in the past
century since 1900," says Australian lead author, Vincent Post, a
groundwater hydrogeologist from
Flinders University in Adelaide.
"Freshwater on our planet is increasingly under stress and strain so
the discovery of significant new stores off the coast is very exciting,"
says Post, who is also with the
National Centre for Groundwater Research and Training.
"It means that more options can be considered to help reduce the impact of droughts and continental water shortages."
UN Water, the United Nations' water agency, estimates that water use
has been growing at more than twice the rate of population in the last
century due to demands such as irrigated agriculture and meat
production.
More than 40 per cent of the world's population already live in
conditions of water scarcity. By 2030, UN Water estimates that 47 per
cent of people will exist under high water stress.
Post says his team's findings were drawn from a review of seafloor
water studies done for scientific or oil and gas exploration purposes.
Prior to this report Post says such undersea water reserves were considered to be rare.
"By combining all this information we've demonstrated that the
freshwater below the seafloor is a common finding, and not some anomaly
that only occurs under very special circumstances," he says.
Underwater aquifers
Post
says the deposits were formed over hundreds of thousands of years in
the past, when the sea level was much lower and areas now under the
ocean were exposed to rainfall which was absorbed into the underlying
water table.
When the polar icecaps started melting about 20,000 years ago these
coastlines disappeared under water, but their aquifers often remained
largely intact -- protected by layers of clay and sediment.
"In some case you have actually have fresh water under the sea, but
in most cases it's a mixture between freshwater and sea water - we call
that brackish water," says Post.
Post says the deposits are comparable with the bore basins currently
relied upon by much of the world for drinking water and could cost much
less than seawater to desalinate.
"For some areas it is economically viable to desalinate that brackish
water and make it economically competitive with other sources of water
recovery."
Post says similar technology to offshore oil exploration.
"You could drill from a platform or drill horizontally under the sea bed," says Post.
Challenges
But,
Post says drilling for the water would be expensive, and Post says
great care would have to be taken not to contaminate the aquifers.
He warned that they are a precious resource.
"We should use them carefully: once gone, they won't be replenished
until the sea level drops again, which is not likely to happen for a
very long time," says Post.
Water resources expert Dr Richard Davis of the Wentworth Group agrees.
While he says this "neglected resource" could become economically
viable to obtain with the drop in desalination costs, humans don't have a
good track record when it comes to exploiting the world's onshore
groundwater resources, such as the Great Artesian Basin.
"We just squandered the water," says Davis, who was previously with CSIRO, the World Bank and the National Water Commission.
"In the Great Artesian Basin case we spent around 100 years pumping
the water to the surface and letting it flow free and evaporate, using
only a very very small fraction of what we tapped," he says.
As a result, says Davis, Australia has had to undertake a very
expensive remedial program to try and cap the free-flowing bores to save
water. He says there are similar stories in Africa and China.
"What concerns me here is that we don't take the same approach again," says Davis.
"Let's be slow, cautious and thoughtful about it this time and show
how we can act responsibly if in fact the economics do stack up for the
use of some of these aquifers."