Some facts:

  • It is estimated by some that up to 12000 dwellings in Glen Eira are subject to flooding. Many of these properties are in the housing diversity areas
  • Large areas of Glen Eira also sit on a water table

The significance of the above is magnified when applications such as the following appear –

Address: 15-17 Belsize Avenue, Carnegie.

Proposal: Construction of a four storey building comprising fifty two (52) residential apartments above two levels of basement car parking

We are not structural engineers. Nor are we hydrologists. But given the prevalence of more and more basement excavation in built up areas within the city, we are starting to wonder what LONG TERM impact such excavations have on water tables, drainage, flooding, and neighbouring properties? Also worth asking is the following:

  • Does council have the necessary ‘expertise’ to adequately assess such an application or will they simply rely on the developer’s paid ‘experts’?
  • Will council consider the cumulative effect, or simply go by its site by site application philosophy?
  • Can council guarantee that neighbouring properties will not be impacted by this proposed deep excavation? What recourse do residents have if things go awry?

We’ve uploaded (HERE) a fascinating report from England which addresses some of the dangers of widespread excavations. Admittedly, conditions in England may be vastly different. However, the warnings they issue are universally applicable. Here are some quotes:

The Report identifies some of the considerations in relation to the effect on the surrounding buildings and areas where the risks may be higher. It also emphasises the need to consider attached properties as part of the same overall structure rather than treating a property in isolation.

Basement construction involves significant engineering structures, which create a permanent irreversible change in ground conditions. The complexity increases rapidly with the depth. This can have a long term impact on the future planning and development within the City of Westminster.

While an individual basement is unlikely to cause any significant change in groundwater levels, the long term cumulative effects need to be considered. In reality potential cumulative impacts will increase as more basements are constructed.

And for a closer to home example there’s this from Adelaide (7th May, 2014) –

DEVELOPERS of the controversial Baju Apartments at Henley Beach could be forced to pay hundreds of thousands of dollars to fix their handling of groundwater at the site.

According to a Charles Sturt Council report, developer Bayspring Pty Ltd has been removing groundwater from the Seaview Rd site without approval from the Environment Department and is in breach of the Natural Resources Management Act.

The basement of the four-storey apartment building, which opened in 2011, sits below the water table, making it susceptible to flooding. Since the apartments were built, groundwater around the basement has been collected and pumped out to sea.

However the Environment Department has told Bayspring the water must be returned to the aquifer and has been in talks with the company to find the best way to comply.

Residents are worried removing the groundwater would allow seawater to seep into the aquifer and change the make-up of the underlying soil, potentially causing cracking in their homes.

A council report has shown more than 134kL of water – the equivalent of one swimming lane of an Olympic-sized pool – is being pumped out to sea each day.

Western Adelaide Coastal Residents Association president Jim Douglas said removing that much groundwater could affect the water table. He said buildings close to the beach could be at risk of cracking or losing stability and the Baju Apartments would likely be the worst affected.

“The people there ought to be concerned about it,” Mr Douglas said. “Its bloody scary…and it is right under their floorboards.”

North St resident Lara Hollamby said the process to fix the issue was taking too long and closer monitoring was needed to reassure residents that damage had not already occurred.

She feared properties in and around Henley Square were at risk of becoming unstable if the removal of groundwater continued. “It’s not fair for residents and the people who live so close. “What recourse can they have if they do suffer damage? They deserve some peace of mind. “The removal of this groundwater has now been going on for years and there has been no meaningful monitoring during that time.”

Reinjecting the water into the aquifer or waterproofing the building are both being considered and could cost anywhere between $300,000 and $700,000.

A spokeswoman for the Environment Department said the practice of removing the water posed “no risk in the short-to-medium term to the integrity of the underlying aquifer”.

The department did not respond to questions about whether Bayspring would be fined for breaching the Natural Resources Management Act.

Colton State Labor MP Paul Caica said the Department had made it clear no damage had yet been done to the aquifer.

However the water needed to be returned to ensure there were no long-term problems.

“It has gone on far too long and it would be nice to have a speedy conclusion,” Mr Caica said.

Bayspring owner Richard Antunes did not respond to queries by press time.