Cargeeg, G.C., Boughton, G.N., Townley, L.R., Smith, G.R, Appleyard, S.J., and Smith, R.A. (1987a), The Perth Urban Water Balance Study, Executive Summary, Water Authority of Western Australia Report and UWA Environmental Dynamics Reference ED-86-192, 20pp.

The shallow groundwater underlying the Perth metropolitan area is a major water resource which meets a large proportion of Perth's domestic, irrigation and industrial water supply demands. This groundwater resource occurs in an unconfined aquifer which is formed by a superficial layer of permeable sediments beneath the Swan Coastal Plain. These superficial sediments occur as a thin veneer, about 60 m thick, overlying 13 000 m of sediments which contain confined freshwater aquifers to a depth of about 1000 m (Figure 1).

While forming an important source of water for man's activities, the shallow groundwater is also an integral part of the natural coastal plain environment, supporting vegetation where the water table is shallow and indigenous flora and fauna at the many wetlands where the water table intersects, or is just below, the ground surface.

Approximately 223 million cubic metres of water are withdrawn each year from the unconfined aquifer of the Perth region for private domestic irrigation, commercial irrigational, local government and institutional irrigation, industrial use and public water supply. Private domestic irrigation draws about 77 million cubic metres each year. Other private water supplies and irrigation utilize about 113 million cubic metres. Public water supplies provided by the Water Authority draw about 33 million cubic metres.

In the below-average rainfall years of the late 1970s, the quantities of groundwater being drawn by the Water Authority, for public reticulated supplies, increased markedly because of reduced availability from surface water resources. Water restrictions were also needed to reduce demand on surface water resources, leading to a significant increase in the number of private domestic bores and wells. There are currently about 77000 domestic bores in Perth, plus other private bores used for irrigating market gardens and public open space and for industrial purposes. This extensive private development of the resource has formed a significant secondary water supply system, effectively reducing demand on the public water supply system.

The accelerated use of groundwater in Perth resulted in concern being expressed within the community that water table levels were being lowered, wetlands were drying up and bores in coastal suburbs were drawing more saline water.

In 1981, an investigation by the Water Authority concluded that this concern was justified but that practical management of the groundwater system in the urban area was feasible. The Perth Urban Water Balance Study was therefore initiated in June 1982 with the following objectives:

To cater for a broad range of readers, the outcome of the Study is reported in the following forms:

Volume 1 of the full report provides an account of the groundwater systems and their need for management, including the conclusions and recommendations of this Study. Volume 2 contains a full discussion of the techniques and methods used to derive the findings and recommendations of the Study.

Figure 2 is a diagrammatic representation of the contents of each Volume and shows the relationship between the different parts of the report.