Woodvale Swimming Pool Collapse
Abstract
Caves and Karst are some of the most vulnerable ecosystems in the world. The Karst Landscape on the Swan Coastal Plain (including Yanchep National Park) represents an important part of the earth’s geological diversity. The limestone in this area of Western Australia exhibits unique characteristics due to the nature of its development.
The geology of the northern suburbs of Perth comprises, in part, a large area of coastal Aeolian limestone (also known as: Tamala limestone and Aeolian calcarenite), observed as a series of distinct landforms roughly parallel to the coast. Several authors have recognized three main units that occur from east to west: The Bassendean Dune system, the Spearwood Dune system and the Quindalup Dune System
During March 2007, a sinkhole developed in a backyard of a residential property in Woodvale. This resulted in the collapse of a swimming pool and the loss of around 44,000 Litres of water overnight. During the months that followed, local and State Government agencies and other service companies assessed the situation without resolution.
In July 2007, Ross Anderson of Dissolved Rock Pty Ltd, contacted Mike and Sonja Pilkington to make the offer of assistance in the investigation of subsurface conditions and possible remedial actions that could be undertaken to stabilise the sinkhole that was evident in the rear north western corner of their property.
The offer entailed a site visit to the property to undertake on ground investigations using Ground Penetrating Radar (GPR), downhole camera equipment and a surface inspection of the property and surrounding neighbourhood.
It was assessed that the connection to the ground surface displayed in the backyard of the property was most likely a solution tube rising from a cavity at or near watertable level. The Perth Ground water atlas estimates that the ground water in the Woodvale area is approximately 15.5 metres AHD. Using available information and cave data an estimate of limestone thickness was made.
Two reports were submitted to the land owners and parliament member Judy Hughes. In the following months the property was bought by the government and remedial works undertaken to fill the depression.
The property was then sold by the government with a notification on the title and restriction of use for the rear northern section of the property. Acknowledgements: Lex Bastian, Ian McCann, Jay Anderson, and Greg Joyce.