Environmental Engineering Reference
In-Depth Information
some water left in them for ecological purposes. This understanding has
come about only after the loss of native fish and the occurrence of extensive
blue-green algal blooms that have reduced the amenity and utility of many
waterways.
We are currently going through a turbulent and exciting period of water
reform. The recent decision by The Council of Australia Governments (COAG)
to create a national water market opens the way for important new policy
opportunities and possible rescue of some of our deteriorating waterways.
The Murray-Darling Basin comprises some 14 per cent of the Australian
landmass, about 1 million square kilometres, and yet has only 6 per cent of
Australia's run-off. It is highly developed for agriculture, supporting about
42 per cent of all Australian farms. The history of water development in the
Murray-Darling Basin is a history of articulate interest groups seeking to
have the waters used for their particular advantage. There has always been a
tension between the upstream States and the downstream State who had dif-
fering views of the public good. These tensions continue, although the issues
now relate to over-extraction of water and salinisation of land and water.
Over some 80 years there has been extensive development of water
resources of the Murray-Darling, and a highly productive irrigation indus-
try has been developed. Unfortunately, much of this development cannot
pass economic nor environmental scrutiny, and there has been considerable
degradation.
We have now learned that many of our water management strategies
have caused great damage to the ecosystem of the Murray-Darling. By trap-
ping winter stream flow we have starved the river of flow in winter and
turned it into a bank-full irrigation channel in summer, totally reversing the
natural flow pattern. We have extracted excessive amounts of water and built
weirs to help distribute the water. These also turned out to provide ideal
habitat for both blue-green algae and for carp. By our water extraction and
our building of levees to control floods we have isolated the river from its
floodplain. This has had massive impacts on populations of native fish and
birds as well as on the River Red Gum forests of the Basin.
Australia is an old and highly weathered landscape, and much of it is very
flat. Soluble salts originate from the weathering of rock minerals and the
deposition of oceanic salt through rain or wind, and are redistributed in the
soil profile and landscape with movements of water. Salinity problems are
most common in semi-arid areas where there is sufficient rainfall to wash
