Environmental Engineering Reference
In-Depth Information
Rivers, Bogan, Condamine-Balonne, Macquarie, Namoi and Warrego Rivers
are expected to exceed World Health Organization drinking levels within 20
years, and the Lachlan and Castlereagh rivers within 50 years (see Table 6.1).
The Avoca and Loddon Rivers in Victoria already exceed this level.
Irrigation in Australia
Irrigation has long been seen as the key to unlocking the wealth of the Aus-
tralian landscape, and myths about making the desert bloom abound. In the
20th century there was a view that any water flowing to the sea was wasted,
and all we had to do was build massive engineering works to harness the
water. These 20th century myths persist amongst some older and influential
Australians.
During the current drought, talkback radio hosts in Sydney started
calling for massive engineering works to droughtproof our country. This led
to the formation of the Wentworth Group of Concerned Scientists who
answered these calls with the response that we would do better if we learned
to live
with
our country and stop our futile attempts at taming it.
Irrigation in Australia uses around 75 per cent of all the water harvested
and was responsible for agricultural production worth $9618 million in
2000-01. In fact, half of the profit from all Australian agriculture comes
from the 0.5 per cent of our land that we irrigate. There has, however, been a
dramatic increase in irrigation, and water use has increased by 59 per cent
between 1983-1996. The competition for water is becoming more intense,
just as the community is starting to appreciate that we have degraded the
health of our rivers by over-extraction. However, much of this water is used
on crops that produce relatively low gross returns (see Table 6.2), and so it
may be possible for water to be better used.
The challenge of assessing river health
Our understanding of how to assess river health has developed rapidly over
the last decade. Prior to that, most assessments were based on water quality
measurements of particular substances in the water. The problem was that
these substances varied over often quite short time intervals, and integrating
the overall effect was difficult, especially when only sporadic measurements
were taken.
In the 1990s it was realised that the biology of the river system gave a far
better measure of river health than water quality measurements, since the
