DARLING RIVERINE PLAINS BIOREGION Background Report

16/08/02 Darling Riverine Plains Bioregion Background Report
occasional sands and brown clays on low rises. A broad, complex floodplain dominated by
high-level grey clay plains lies between the confluence of the Barwon and Macquarie Rivers
and Bourke.
Culgoa-Bokhara Province
Grasslands or forbfields occur on the plains of quaternary alluvium of the Culgoa and
Bokhara Rivers. Grey clays predominate on the floodplains, with some texture contrast soils
on low rises. These low level flood plains and channels contain extensive areas of Astrebla
(Mitchell grass) grasslands, much of which has been heavily grazed and cultivated. In many
areas the Astrebla grasslands have become degraded and are now replaced by opportunistic
weed species such as Sisymbrium (mustard weed).
Warrambool-Moonie Province
This province contains no major river but is cris-crossed by a complex of distinct channels
(the Big Warrambool). The channels are usually dry but are filled periodically by high level
overflows of the Moonie and Balonne Rivers to the north. The channels are usually dry. The
landform varies from low-level floodplains and channels to high-level floodplains, low rises
and high-flow channels. Grey clay soils occur on the floodplains, and texture contrast soils
and sands occur on low rises. The vegetation of this province is generally quite open with
Eucalyptus coolabah (coolibah) and Eucalyptus populnea subsp. bimbil woodlands on the
higher areas. Much of the land is heavily grazed and some areas are cultivated. The low red
rises are generally severely scalded.
Narran-Lightning Ridge Province
A dominant feature of this province is a north-south ridge of Cretaceous sediments, adjacent
to low-level Quaternary alluvials on the floodplains. The Narran River, which lies to the west
of the ridge, receives flow from low-level floods in the Balonne-Maranoa River system in
Queensland. Water from this system mostly flows around the ridge and is retained in a large
number of basins formed around the lower slopes. The largest of these basins is Narran Lake,
the terminal basin for the Narran River. The Narran wetlands are terminating basins with little
or no flushing. They also receive a large quantity of local runoff from the adjacent
sedimentary ridge. During high flows this basin overflows to the west and the Narran River
overflows to join the Big Warrambool (Province 4).
The two most common landforms in this province are low rounded ridges and some rocky
hills with Eucalyptus melanophloia (silver-leaf ironbark) open woodland and level to gently
undulating floodplains, low rises and sand dunes with a riparian woodland. There are also
depressions and backplains, lunettes, salinas and levees where grasses, forbs and some
riparian plant communities occur. The soils on the ridge vary from red earths to lithosols and
grey clays are again dominant on the plains.
Collarenebri Interfluve Province
This province is the southern-most tip of the Northern Surat Basin, an extensive region of
coarse-grained deeply weathered Cretaceous sediments in south-eastern Queensland. This
narrow area of land west of the Barwon River is slightly undulating, with low rounded hills. It
separates the parts of the DRP bioregion that receive drainage from Queensland from those
fed mainly by drainage from the slopes and tablelands of New South Wales. The loamy deep
red earths of this area are easily compacted and susceptible to water and wind erosion
following clearing of the Eucalyptus populnea subsp. bimbil woodlands in this province.
56