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and southern New South Wales had much higher late Pleistocene flood discharges
andbedloadsthantheydotoday.
There is some evidence of a link between variations in river discharge and sediment
load and short-lived phases of glacial and periglacial activity in their headwaters in
the Eastern Highlands of south-east Australia (Williams et al.,
2009b
). The three
youngest glacial advances in the semi-arid Snowy Mountains of south-east Australia
have yielded
10
Be cosmogenic nuclide ages of 32
1.4 ka
(Barrows et al.,
2001
; Barrows et al.,
2002
). Periglacial deposits range in age between
23 and 16 ka, with a weighted average age of 21.9
±
2.5, 19.1
±
1.6 and 16.8
±
0.5 ka (Barrows et al.,
2004
).
Episodes of at least seasonally very high river discharge in theMurray, Murrumbidgee,
Lachlan and other major rivers draining the south-east uplands have been dated by
14
C, TL and OSL to approximately 35-25 and 20-14 ka (Bowler,
1978a
;Pageetal.,
1991
; Page et al., 1994; Page and Nanson,
1996
;Pageetal.,
1996
;Ogdenetal.,
2001
;
Page et al.,
2001
;Bowleretal.,
2006
). Reinfelds et al. (
2014
) have shown that in the
Snowy Mountains today, run-off decreases by 17 per cent for every 1
±
C increase in
annual temperature and proposed that lower LGM temperatures could have more than
doubled run-off rates in that region.
The onset of the modern flow regime in the Riverine Plain of south-east Australia
appears to be somewhat younger than the 16 ka start of deglaciation in the Snowy
Mountains (Ogden et al.,
2001
; Barrows et al.,
2001
). No doubt an extensive winter
snow cover persisted in the headwaters well after the valley glaciers had melted,
contributing to high rates of seasonal river discharge. Late Pleistocene periglacial
solifluction deposits are widespread in the uplands of south-east Australia (Bowler
et al.,
1976
), and these would have provided an ample supply of coarse debris to
streams during the spring snow-melt season.
Further north, beyond the limits of glacial and periglacial action, the sparse vegeta-
tion cover characteristic of the cold, dry late Pleistocene climate would also have been
conducive to initially high rates of run-off and a relatively high load of coarse sedi-
ment, reflected in large streamchannel dimensions out on the alluvial plains west of the
uplands (Williams,
1984e
; Williams,
2000
b; Williams,
2001a
; Williams,
2001b
). As
the climate became warmer, the plant cover became denser and soils began to develop,
leading to a change from traction-load to mixed load to suspension-load channels.
With the decline in rainfall during the past 5,000 years, the previously wide mean-
dering channels became progressively smaller, with shorter meander wavelengths,
culminating in the modern 'underfit' rivers, dwarfed by their late Pleistocene and
early Holocene ancestors. Much of the evidence for late Quaternary climate change
in south-east Australia comes not so much from the rivers themselves as from pollen
analysis and studies of the lakes in this region (Williams et al.,
2009b
).
Fried (
1993
) suggested that the suspension load in the late Quaternary Riverine
channels could have come from wind-blown dust, so that the large meanders could
reflect the dust input rather than hydrologic changes in the headwaters. Later workers
°
