WESTERN AUSTRALIA: MANAGING WATER
Department of Water staff deep underground in Yanchep measuring Gnangara aquifer levels. One of 700 monitoring stations on Gnangara, it is regarded as one of the best monitored groundwater systems in the world.
programme; large scale groundwater replenishment; and construction of two desalination plants. All of these help Western Australian become less climate dependent for both potable water and water for industry and agriculture.
Keeping Perth hydrated Since the late 1990s groundwater had taken over as the major source for the private and public water supply for Perth, the State’s capital city. Today, the reliance of the greater Perth metropolitan area on what is currently more than 430GL a year of groundwater for a total water supply of around 550Gl a year, is certainly one of the biggest water challenges for the State.
The Gnangara groundwater system stretches 2,200 km2 under the largely urbanized Swan Coastal Plain north of the Swan River between the Indian Ocean and the
Darling Range. The system has for many years supplied up to 300GLs of Perth’s water – including half of Perth’s public water supply. This water, which comes from both deep and shallow aquifers beneath the city, supports fresh fruit and vegetable production, parks and ovals for recreation and sport, schools, industry, small businesses, local government. It has been estimated that the water from the Gnangara system alone supports in perpetuity more than $6.7 billion of economic activity.4
Rainfall around the State’s capital – where around 80 per cent of our population is - has dropped by around 15 per cent since the mid-1970s. More recently, the average has dropped from 766mm in 1990-1999 to 683mm from 2000-2009, and since 2009 has fallen again to an average of 656mm.
Prior to 1974 the average inflow 168 | The Parliamentarian | 2014: Issue Three
into Perth Dams was over 330GLs a year. From 1975 to 2000 average inflow was almost half this value at 177GLs. From 2001 onwards the inflows again halved, and in 2010, the driest year on record, only 13GLs of water ran into the dams – effectively ending their reliability.5
This is now a topic of regular media reporting and only recently an article published in the premier international science journal Nature Geoscience reinforces accepted climate modelling that the drying trend in the Southern half of Australia – particularly out State’s South West – is real and likely to continue.
The State water scientists, again in collaboration with agencies such as the Commonwealth Science Industry Research Organisation (CSIRO), have recorded the impact of this rainfall decline on surface water yields, and have found that a 10 per cent reduction in rainfall can result in up to,
and in some cases more than, a 30 per cent reduction in streamflow and run-off into dams.6
These dams that once provided all of Perth and the Goldfields’ water, are now on average expected to provide less than 20 per cent of the water distributed through the Water Corporation’s Integrated Water Supply Scheme.
Perth’s continued high growth rate under the drying climate has pushed the State further to use, and find ways to support, groundwater supplies. Thankfully though, this work was not a case of shutting the door after the horse had bolted. The investment in groundwater knowledge has been building since the 1970s.
Western Australia built and has since managed the nation’s first major public water supply desalination plants. The two modern reverse osmosis desalination plants provide us with the capacity to supply 145
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