Australia Yearbook - 2001

594 Year Book Australia 2001
14.24 SOURCE OF NET WATER CONSUMPTION, By Sector—1996–97
Agriculture(a)
Mining
Manufacturing
Electricity and gas
Water supply
Household
Mains supplied
Self-extracted
0 2000 4000 6000 8000 10000
GL
(a) Agriculture includes services to agriculture, hunting and trapping and forestry and fishing.
Source: Water Account for Australia, 1993–94 to 1996–97 (4610.0).
Effects of water resource
development on Australia’s
freshwater environments
Water resource development, including both dam
operations and water diversions, has influenced
the hydrologic and ecological characteristics of a
number of river systems across Australia. The
once highly variable flow regimes of rivers found
in semi-arid environments such as Australia have
been substantially reduced and replaced by stable
flooding regimes. In some cases, as well as a
reduction in the annual flows there has been a
distinct contrast in seasonal flooding
characteristics. For example, peak flows for the
Murray River at Albury under natural conditions
(without dams and water diversions) occurred in
September and October, with minimum flows
occurring in February. In marked contrast to this
flow regime it has been found that under current
conditions (with dams and water diversions),
peak flows now occur in January to March, with
minimum flows occurring from June to
September (MDBC 1995). Although water
resource development has been an integral part
of Australia’s domestic and economic
development, it has dramatically affected the
health of many river systems.
There are many varied effects of changing flow
regimes brought about by water resource
development. Alteration of flow regimes, with
both changes in flow patterns and a reduction in
flow variability, has distinctly altered river
channel, floodplain and wetland characteristics.
Changes in inundation patterns of both
floodplains and wetlands have altered biological
and ecological processes, decreasing overall
biodiversity and particularly breeding
opportunities for wetland water birds (Kingsford
2000). Changes to in-channel flow have enhanced
channel and bank erosion, consequently
decreasing channel complexity and hence habitat
availability for aquatic species. Clearing of riparian
vegetation allows increased sediment into the
rivers, which can add nutrients and pollutants
that are harmful to aquatic species and to overall
water quality and river health. Algal blooms have
occurred as a result of increased nutrients
(phosphorous and nitrogen) combined with
reduced oxygen levels and stagnation, which both
occur in reduced flows (MDBC 1995). Extended
irrigation and tree clearing practices have also
caused a rising water table and exacerbated the
naturally saline ground water levels in much of
the country. The spread of dryland salinity is
mirrored by continually increasing salt loads in
freshwater systems across Australia. For example,
it is estimated that the salts loads in the Mallee
zone of the Murray River (from the South
Australian border to Morgan) will increase from
330,000 tonnes per year to 610,000 tonnes per
year by 2050 (MDBC 1999). Further information
on these issues is provided in Australia’s
Environment: Issues and Trends, 2000 (4613.0).