Geoscience Reference
In-Depth Information
increased flowering, seed release and seedling
survival (Jensen, 2008), most environmental
watering to date has been
ad hoc
projects rather
than long-term, managed regimes.
on the Finniss River was later abandoned). The
Clayton regulator averted the perceived threat
of acidification, although the impounded water
became saline.
A 20-year Long-Term Plan for the Coorong,
Lower Lakes and Murray Mouth has been
prepared by state and federal governments in the
context of extended drought, falling lake levels and
exposed margins, the loss of wetland ecosystems
and the perceived threat from acid sulphate soils
(http://www.environment.sa.gov.au/cllmm/the-
long-term-plan.html) (DEH, 2010; Kingsford
et al
.,
2011). The plan included a proposal to pump
hypersaline water from the Coorong to the ocean,
to lower the salinity to levels that would support
Ruppia tuberosa
, a key food plant, and associated
populations of invertebrates, fish and birds (Paton,
2010). The plan provided also for treatment of
acid sulphate soils using powdered limestone, and
extensive planting around the margins of the lakes.
It had been expected to take some years,
given average rainfall, to re-wet the catchment
soil and refill the storages, but a rapid switch
from El Ni no to La Ni na weather conditions in
mid-2010 produced the highest recorded spring
rainfall in south-eastern Australia. In August-
September 2010, rainfall in the Lower Lakes
region and in upper catchments of the Murray
and its tributaries generated flows that restored
lake levels to
Present conditions
In 2002 the Murray Mouth was closed by
coastal sand deposition, and required continued
dredging until late 2010, costing A
$
5.2M annually
(Kingsford
et al
., 2011). The initial closure resulted
from a lack of river outflow, caused by increased
diversions rather than drought, and no flows
passed the barrages from 2006 until September
2010. Most discussion over the need to maintain
an open river mouth has referred to diadromous
fish and the salinity of the Coorong, and hence
to plant and waterbird populations (Paton, 2010;
Kingsford
et al
., 2011), but the need to flush long-
term accumulations of salt, sediment and nutrients
must also be considered (Bourman and Barnett,
1995; Bourman
et al
., 2000).
In 2007-2010, river levels downstream of
Blanchetown (273 km from the mouth) fell by
more than 2 m, leaving the Murray shallow and
less than half its normal width, causing river
banks to collapse in some areas and endangering
property (Plate 27). In 2009, a temporary 'bund'
(an earth embankment) was constructed to isolate
Lake Albert, and water was pumped from Lake
Alexandrina to prevent the level of Albert falling
below
−
0.37 m AHD and exposing acid sulphate
soils (Plate 28). By August 2010, Alexandrina had
regressed from its regulated level of
0.65 m AHD by early October,
and impoundments throughout the Basin were
returned to full capacity. The inflows in September
2010 flooded acid sulphate soils around the lake
margins and restored flows through the barrages to
the Coorong, and dredging at the Murray Mouth
halted in October 2010 (http://www.mdba.gov.au/
water/waterinstorage). As levels rose in September
2010, the temporary weirs subdividing the Lower
Lakes were breached (partly removed), although it
is not clear whether all will be removed entirely.
The plan to pump hypersaline water from the
Coorong has been delayed.
With improved conditions in early October 2010,
and lakes Alexandrina and Albert at 90% of normal
regulated levels, management priorities began to
move away from short-term responses. However,
while
+
+
0.75 m AHD
to less than
1.0 m AHD.
In 2009, another temporary earth weir (a
'regulator') was constructed at Clayton to isolate
the Goolwa Channel (the lowermost reach of the
river before the mouth) (Plate 29). Again, its
main purpose was to maintain the water level and
prevent exposure of acid sulphate soils, although
there was also some speculation initially about
the need to maintain this area as 'a freshwater
ecological refuge'. The Goolwa Channel receives
inflows from two small streams between Clayton
and Goolwa (Currency Creek, Finniss River), and a
further low-level regulator was constructed across
Currency Creek (a plan for a similar embankment
−
inflows
from
the
Murray
to
the
Lower
