DARLING RIVERINE PLAINS BIOREGION Background Report

16/08/02 Darling Riverine Plains Bioregion Background Report
Catchments
There are six major river catchments within the DRP (Map 19, Table 2.3). The Western and
Macquarie River catchments together cover 67% of the DRP and contain most of the
wetlands.
Table 2.3 River catchments intersecting the DRP
Catchment Area within % total % DRP
DRP (ha) catchment area
Western including Barwon, Birrie, Bokhara, Culgoa, 3 472 620
Darling, Little Weir, Moonie, Narran, Paroo and Warrego
Rivers
12% 38%
Macquarie River including Barwon, Bogan, Darling, and 2 710 519
Little Bogan Rivers
36% 29%
Gwydir River including Barwon, and Mehi Rivers 910 366 34% 10%
Castlereagh River 853 068 49% 9%
Namoi River 779 814 19% 8%
Macintyre River including
Barwon, Boomi, Doondoona, and Dumaresq Rivers.
522 455 22% 6%
Western Catchment
The Condamine-Culgoa River system in south-central Queensland feeds the Culgoa and
Bokhara Rivers of the western catchment. Beardmore Dam at St George regulates these
rivers and an increase in water diversion for cotton irrigation has substantially reduced the
river flow from Queensland into New South Wales. These rivers are mostly fed by summer
floods from cyclonic depressions and are strongly seasonal.
The Narran River is also part of this system but it does not feed into the Darling system,
terminating instead at Narran Lake and associated wetlands. It is unregulated with minimal
water extraction occurring. It also receives flows from the Balonne River during periods of
high flow, although the Balonne is regulated by Beardmore Dam and water is also extracted
to on-farm water storages, affecting the flows into the Narran system.
The Narran Lakes are a large terminal lake system at the end of the Condamine - Balonne
River system (Map 20). The Narran River has a small shallow main channel with a
contiguous floodplain and several lakes lie along the floodplain. During a large flood event
the Narran branches to fill Clear Lake while simultaneously flowing to and filling Narran
Lake. Once Clear Lake has filled it overflows to fill Back Lake and the Long Arm and more
water flows into Narran Lake (Ramsar 2000).
Flooding mostly occurs in summer and autumn, but floods have been recorded in winter and
spring. Annual inflows are highly variable and more than one flood per year has occurred
during a quarter of the recorded flood events. Once inundated, Narran Lake can hold water
for up to 2 years, but in years of low flow water may not reach Lake Narran at all. Back and
Clear Lakes, which are within Narran Lake Nature Reserve, will usually retain water for
about 4-6 months after a single inundation. As a terminal system the lakes usually empty only
by evaporation and seepage but during exceptional events the Lakes can overflow to the
Barwon River. These lakes have an average inundation frequency of one per two years and
this is more frequent than for other inland wetlands in New South Wales (Ramsar 2000).
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