The flooding of an empty building pit is believed to have played a key role in the formation of two sinkholes the opened up next to an apartment block in Sydney.

The appearance of two potentially hazardous sinkholes in a pair of adjacent housing blocks situated in western Sydney has resulted in the evacuation of around 50 local residents.

The two sinkholes appeared mere centimetres away from an apartment block in the centre of Parramatta following stormy weather in Sydney’s west over the weekend.

Residents were evacuated from the building on Saturday, with some reportedly given mere seconds to leave due to the urgency of circumstances. They have since been forced to find accommodation elsewhere, leaving their household belongings in the affected properties.

The apartment owners made haste by Monday night to arrange for the stopgap remedy of pouring concrete into the sinkholes up in order to prevent the ground beneath the buildings from further crumbling.

According to geotechnical engineers who have examined the site, however, full repair work could take anywhere between a few days to a few weeks to complete.

Engineering experts speculate the heavy rain was the chief factor behind the sinkholes, flooding the empty pit of an adjacent building site and causing widespread soil erosion.

The building site located next to the apartment buildings has remained empty for over decade despite its owners obtaining approval for the construction of new units back in 2005.

According to local residents, the empty pit has frequently been flooded with water, compelling authorities to issue an order to owner Guang Tian International Group to deal with the problem of stagnant water on site.

Rainfall and water accumulation play key roles in the ground subsidence that causes sinkholes to form in heavily built up areas.

Water in the ground becomes acidic after absorbing carbon dioxide and interacting with decaying vegetation. This acidic water can erode certain earth types – in particular those comprised of materials that readily dissolve such as limestone.

The ground erosion process is one that rapidly builds momentum once it begins, with dissolving limestone producing larger pockets and crannies for even more acidified water to accumulate, further hastening the process.

Sinkholes form once the eroded earth beneath the surface of the ground collapses, leaving a gaping crater in its wake.

Given that acidified water is the chief cause of subterranean erosion, the accumulation of large bodies of water in the ground, whether in the form of an artificial pond or flooded building pit, can contribute significantly to sinkhole formation.

Parramatta Lord Mayor Scott Lloyd has since called for the expansion of local government authority to address the problem of building sites being left idle for extended periods of time as a result of stalled projects.

Lloyd has called in particular for local government to be conferred with the authority to order developers to clean up construction sites once they’ve gone 18 months without significant progress.