Measuring vulnerability of seawater intrusion

Salt water from the Indian Ocean about to meet fresh water from Moore River, Western Australia. © iStockphoto
Salt water from the Indian Ocean about to meet fresh water from Moore River, Western Australia. © iStockphoto

A team of Flinders University researchers has developed a new method for predicting how much seawater will intrude into underground water storage systems in the future.

Led by Associate Professor Adrian Werner, from the School of the Environment, the team has devised a new maths-based approach to estimate the vulnerability of coastal aquifers to seawater intrusion, with the research recently published in the international journal Ground Water.

Seawater intrusion is a major problem that occurs in coastal areas as a result of salt water encroaching from the ocean into freshwater storage systems below the earth’s surface, known as aquifers, contaminating the water stores.

“Seawater is denser than freshwater so it pushes into the aquifer in a wedge-like shape,” PhD candidate Leanne Morgan, who helped develop the new method, said.

“When you stress the system, predominately by removing too much water, the wedge moves inland and contaminates the freshwater, meaning, for example, bores go salty – it can often be very sudden and unexpected, and sometimes virtually irreversible.”

Unlike the existing, subjective methods for rapidly assessing seawater intrusion vulnerability, Ms Morgan said the Flinders approach was theoretically based, employing both maths and physics to estimate the sensitivity of aquifers to different stresses, for example climate change.

“We took an existing mathematical model for estimating the extent of seawater intrusion and extended it using calculus to develop equations that describe the propensity for seawater to move into aquifers under different stresses, including sea level rise, pumping and recharge change.”

Meanwhile, Ms Morgan is working on a wider study, funded through the National Water Commission, to identity high-risk aquifers along Australia’s coastline.

Results of the National Scale Vulnerability Assessment of Seawater Intrusion study – a collaboration between the National Centre for Groundwater Research and Training and Geoscience Australia – are expected to be released next month.

“More than 85 per cent of Australians live within 50km of the coast and with the population increasing and climate change pressures, it’s important to assess the threats to coastal aquifers because they are a major water resource,” Ms Morgan said.

“The concern is that with increased extraction, rising sea levels and reduced recharge due to reduced rainfall, our coastal aquifers will become more at risk from seawater intrusion.”

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2 thoughts on “Measuring vulnerability of seawater intrusion

  1. Dear Ms Morgan and Prof Werner,
    The Western Adelaide Coastal Residents Association (WACRA)is currenty very concerned with a new residential and retail development within approximately 100 metres of the sea at Henley Beach. The groundwater management method used to protect 2 levels of underground parking is to pump out the equivalent of 1.8 olympic swimming pools of groundwater every week. The extracted water is released on to the beach. Our Association is very concerned at the possible impacts of a resulting cone of depression involving drying of clay sediments, subsidence and the possible ingress of seawater into the water table. We have raised our concerns with Council, the Department for Water and the Minister for the Environment. The Dept for Water is currently investigating. We are also currently before the Environment Resources and Development Court regarding an application for the next stage of this development. Salinity was measured in December or late November 2011 as 3540 µS/cm at the beach outlet and 3560 µS/cm in the groundwater dewatering tank, but we have no later measurements. We would greatly appreciate any advice you could provide on the situation we are facing here in relation to the vulnerability to seawater intrusion. We would be very peased to meet with you and discuss, and/or to show you the situation here first hand.
    Yours sincerely,
    Paul Laris
    Vice-President, WACRA

  2. Dear Paul,

    Happy to chat – I’ve emailed Jim separately using his WACRA email address with more details.

    Regards,
    Adrian

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