AUSTRALIA’s DAM STORY (Part 1)
Measured across the continent, Australia receives an average of only 465 mm of rainfall a year, compared with Europe's 640 mm and Asia's 600 mm. High evaporation allows just 12 per cent of its rainfall to run off and reach waterways. Even so, there's enough water for everyone—but it's seldom in the right place at the right time.
European settlers solved this problem with dams. The first two—Yan Yean outside Melbourne and Lake Parramatta, Sydney—were completed in 1857. Dam building continued steadily until after World War II, when it accelerated. Today,
500 large (more than 15 m high) dams store a total of 93,957 gigalitres (Sydney Harbour holds about 562 GL). There are also countless smaller dams, called weirs, on most Australian rivers—8000 in the Murray-Darling Basin alone—and more than 2 million farm dams.
Large dams bring quick benefits. They can provide water and electricity, mitigate flooding and create beautiful lakes. But they also have adverse impacts. The first are those on people living in the way of a dam and its lake. They may need to be moved, causing families and communities to fragment. The lake may flood farmland or natural landscape. Many of the drowned river's plants and animals fail to adapt to lake conditions. Alien fish species, introduced into the reservoir accidentally, or for recreational fishing, may further alter the biological make-up of water life, and weeds and algae may thrive in the nutrient-rich water. Downstream, changes in the river's flow and water quality usually cause irreversible effects, often down to the river mouth and beyond. Fish
migration and reproduction, siltation and salinity in deltas are altered.
Once upon a time, these adverse impacts—some of which take years to manifest—weren't really considered before a dam was built. The human need for water, for drinking or to grow food, took precedence. Some people believe they should still. But over recent decades, science has deepened our understanding of natural systems, which we now know can't be broken into discrete pieces, some of which can be exploited and others not. This has given rise to the idea that the
environment itself is a legitimate water consumer, with attendant needs and rights. All this calls for careful study of a river's state and function before it's dammed.
Australia's newest megadam straddles a gentle valley on the Burnett River, 260 km north-west of Brisbane. Apart from a soupy stain low on its upstream face, the concrete is spotless and dazzles the eye under the sharp Queensland sun. This is Paradise Dam, completed in 2005. Impressive though it may be, Paradise, like other large dams, is a mix of good points and bad. For some people, the bad prevail. High among the complaints has been that the rationale behind it was political. Then there are the potential environmental impacts downstream, especially around the river's mouth in Hervey Bay, which worry people such as commercial fishers and tourism operators.