DARLING RIVERINE PLAINS BIOREGION Background Report

16/08/02 Darling Riverine Plains Bioregion Background Report
7.1.2 Hydrological regimes
The Mehi, Macintyre, Namoi and Macquarie Rivers, and Moomin, Carole, Gunningbar, and
Duck Creeks are regulated rivers and parts of the Gwydir and Darling Rivers are also
regulated. Regulated rivers are those that “have large dams supplying irrigation water (and
some town and industrial water) for substantial distances downstream. Downstream tributary
inflows are typically supplemented during the irrigation season, resulting in fairly stable and
unnaturally high water levels. River flow is substantially reduced during the non- or lowirrigation
seasons. At any time of year in periods which would normally have high or very
high flow, flows may be substantially reduced by the trapping of water in a large dam” (EPA
2001). River Management Committees are considering and implementing environmental
flows to improve this flow reduction.
The Castlereagh River and all other streams within the Castlereagh catchment in the DRP, the
Bogan River, Whalan Creek, Thalaba Creek, Marra Creek, and Talyawalka Creek are
classified as unregulated rivers. Unregulated or uncontrolled streams are those streams where
“flow patterns are largely natural. Flows can occur in these streams from local runoff. They
are typically ephemeral (flowing only during floods and freshes). Frequently, they open into
or flow through wetlands and billabongs” (EPA 2001).
The Barwon, Culgoa, Birrie, Bokhara, Narran, and Boomi Rivers, the Gwydir Watercourse
and Pian Creek, and the parts of the lower Gwydir, lower Macquarie and upper Darling
Rivers are classified as controlled rivers with reduced flow. Controlled rivers with reduced
flows include:
1. “River reaches downstream of the major regulated sections where the water is extracted or
diverted. Flow is generally reduced throughout the year. Water is delivered from the main
stream for stock, domestic, some irrigation, and town water supplies several times a year.
2. Sections of rivers immediately below town water supply dams, where water is diverted
directly from the dam. Flows can be substantially reduced throughout the year, though
special environmental releases may be possible” (EPA 2001).
The majority of the bioregion is categorised as either over-extracted in relation to
groundwater or with an extraction level of greater than 100% of the sustainable yield for
groundwater systems. Two smaller areas in the east and south of the bioregion have a total
extraction level of between 70 and 100%. The remainder of the bioregion has an abstraction
of greater than 30% sustainable yield. This area is mostly the Darling riverine corridor of the
bioregion (EPA 2000).
EPA (2000) lists good-quality (or low-salinity) ground water as that found in aquifers
including those in the Darling River corridor. The yields from aquifers within the Darling
River corridor are generally low and more suitable for domestic and stock use or small-scale
irrigation (for example, for orchards). Aquifers that have good-quality water and high yields
within the DRP include the river corridors of the Namoi and Upper Gwydir. These aquifers
are used mainly for irrigated agriculture and stock watering, but potable water extraction is
also an important use. Ground water from the aquifers bounded by the Lachlan, Darling and
Bogan rivers and the south-western corner of the State is generally of poor quality or
extremely low-yielding (EPA 2000).
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