Understanding water pressures

By November 20th, 2019

With many surface water storages, such as reservoirs, empty or critically low, groundwater (underground aquifers fed by rainfall and found in cracks or pores in rock) supplies are critical for many Australian communities and industries.

Across Australia, countless regions are facing water stress. Successive droughts in already dry areas mean some communities could completely run out of drinkable water.

Similarly, over recent years agricultural growers across most of Australia have suffered from unreliable rainfall – too little, too early or too late.  It is widely accepted that water is the most universally limiting factor in Australian agricultural production systems – an industry worth $60 billion a year to our economy.

With many surface water storages, such as reservoirs, empty or critically low, groundwater (underground aquifers fed by rainfall and found in cracks or pores in rock) supplies are critical for many Australian communities and industries.

In fact, groundwater makes up around 17 per cent of Australia’s accessible water resources, as well as accounting for around a third of our total water consumption. Our groundwater resources support communities, industries and the environment.

But groundwater supply faces pressure too – from climate change, contamination, and over extraction, among others.

With so many pressures and so many end users, how do we best manage the resources we have available?

Being Australia’s national science agency, there’s one good place to start: with the collection of new data.

Looking to the north

In 2018, CSIRO delivered the Northern Australian Water Resource Assessment (NAWRA), the most extensive, integrated assessment of northern Australia’s water resources.

The Assessment focused on three study areas: the Fitzroy River catchment in Western Australia; the Finniss, Adelaide, Mary and Wildman river catchments in the Northern Territory; and the Mitchell River catchment in Queensland.

In WA, the Fitzroy River catchment’s largely untapped aquifer systems were found to be key in the area’s potential for irrigated agricultural development.

This water in the local sandstone aquifers is either artesian or close to artesian across large areas. That is, it is stored in the geological layers under pressure and requires no pumping where artesian, or little pumping where close to artesian, thereby minimising operational costs for pumping water to the surface.

The Assessment team’s hydrogeological assessment considered a number of factors in producing its findings.

To better understand the quantity of groundwater in the study area, the team used pre-existing geological, geophysical and groundwater data to design a program of targeted field investigation. It looks to fill the knowledge gaps in our understanding of the extent of aquifers, how groundwater recharges and flows, and how aquifers connect.

Pre-existing geological, geophysical and groundwater data sets were used to design a targeted field investigation program that could address existing knowledge gaps on aquifer extents, groundwater recharge and flow, and inter-aquifer connectivity.

Drilling of the Grant Group sandstone.

The team then drilled at 19 new sites using ‘purpose-built’ infrastructure for groundwater level monitoring, recharge and connectivity assessments. The drilling provided new information on the thickness and extent of different geological units which hold the water, but more importantly provided additional sites for sampling environmental tracers in groundwater.

They made use of environmental tracers (naturally occurring or anthropogenic chemical compounds or isotopes in the groundwater) as well as new information on the thickness and extent of different geological units which hold the water.

Environmental tracers are used to understand the hydrologic properties of aquifers, such as groundwater recharge rates and groundwater flow paths. Groundwater chemistry information will be used to establish the interaction between aquifers and identify rocks through which water has flowed.

All of this new information was then used to help refine existing conceptual models, providing a model and framework of the aquifer’s inflows and outflows of water, and to evaluate the overall potential volume of groundwater suitable for extraction.

The team found that Fitzroy sandstone aquifers are replenished – or recharged – from intense wet-season rainfall events where the aquifers outcrop at the surface. Groundwater hydrologists who worked on the Assessment estimated the mean annual recharge to be 3,500 gigalitres (GL), equivalent to seven times the amount of water in Sydney Harbour.

“The Assessment found that with appropriately-sited groundwater bores, it is possible for up to 120 GL/year (< 5 percent of recharge) of groundwater could be extracted for irrigated agriculture,” said CSIRO hydrogeologist Andrew Taylor.

This means the region could grow cotton, grains or higher-value crops such as bananas, melons and mangoes with a reliable source of water.

“Investing in water infrastructure could unlock about 160,000ha of agricultural land along the Fitzroy River, delivering more than 5000 jobs and creating an agricultural hub worth more than $1.1 billion,” WA Agriculture Minister Alannah MacTiernan told WA media.

But what about areas that don’t have extensive aquifers regularly replenished by monsoonal rains?

Water water everywhere, not a drop to drink

Despite being located in the middle of the ocean, Norfolk Island relies on rainwater tanks and underground aquifers for the bulk of its water supply. And like many other sub-tropical south Pacific islands and communities, it is experiencing changing weather patterns, including reductions in rainfall, extended dry spells and rising temperatures.

This has resulted in unprecedented water stress in recent times, as well as reports of depleted supply.

It is thought likely that these reductions in the recharge of groundwater have occurred on Norfolk. However, no holistic analysis of the Island’s water resources has ever been undertaken, and there is uncertainty about whether current demands on Norfolk’s groundwater can be sustained.

To get a picture of Norfolk’s water resources, CSIRO has begun a program of data collection and field measurements across the island with assistance from the local community.

Our team is currently measuring water infiltrating into the soil, surface runoff, groundwater levels, storage and flow, water used by vegetation and water used by participating households on the Island.

A lack of hydrological data on Norfolk Island means that anecdotal information and records, such as bore drilling logs and stories of water presence and flow of the past, will be vital to the success of the Project.

Specifically, the team will be collecting ground, surface and rain water samples to analyse chemistry and measure the presence of environmental tracers, similar to analyses performed in the Fitzroy. This includes using LiDAR technology, which is a surveying method that measures distance to a target by illuminating the target with laser light and measuring the reflected light with a sensor.

These data will help the community better understand how much water can potentially be extracted from the groundwater systems on Norfolk Island and determine the suitability of aquifers for managed aquifer recharge. In turn, this will inform the Norfolk Island community when it makes future decisions about the use of its groundwater resources for its water supply.

The work that is currently being undertaken by CSIRO is vital for Norfolk Island as it will give us the tools to make informed decisions around water availability and security,” says PJ Wilson, Norfolk Island Regional Council Team Leader, Waste and Environment.

“The reality is that we could run out of water tomorrow.”

“The results from this project should give us a sound base for how we are currently placed in terms of water availability and provide methods to improve water security into the future.”

 

 

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