The Environment Institute
Water Research Centre
Water Wednesday
Managing the Murray Icon Sites:
can engineering save the environment

The Environment Institute
Where ideas grow
Future options for the Lower Lakes
Kane Aldridge, Justin Brookes and George Ganf

The Lower Lakes & Coorong

The Lower Lakes: a predominately fresh
system
Adapted by John Tibby from Fluin et al., 2007

Variable salinity regime
200
Barrage flow (GL/day)
150
100
The natural flow regime and
salinity balance
50
• Spring floods and summer low
0
flows
1975 1980 1985 1990 1995 2000 2005
-50 • Salt intrusions did occur, but never
60 marine
• Small ‘backflow’ events had a
EC (mS/cm)
40
rapid, short-lived impact on
salinity
20
• ‘Fresh’ 95% of the time
0
1975 1980 1985 1990 1995 2000 2005 Data from Bigmod, MDBA

Water level variability
200
Barrage flow (GL/day)
150
The natural flow regime
100 • Water levels fluctuating
between 0.8 and 0.1 mAHD
50
0 • Highly variable from year-to-
1975 1980 1985 1990 1995 2000 2005 year
-50
1
• Salinity and water level
Water level (mAHD)
0.8 primarily determined by Murray
0.6
inflows
0.4
0.2
0
1975 1980 1985 1990 1995 2000 2005
Data from Bigmod, MDBA

The Lower Lakes: a macrophyte
dominated system
Anecdotal evidence of abundant
flora (Sims and Muller, 2004)
• “…reeds, bulrushes and waterweed
grew around the lake”
• “…encircle Lake Albert in one
continued belt”
• “…the shores were also covered
with reedy flats, which were in
some places half a mile in breadth’
Increased habitat and food
complexity for fish and birds
Image: www.wisconsinlakes.org

Connectivity: the key to
resistance and resilience
• A large, dynamic
estuary
• Fresh-hypersaline
• Spatial and temporal variability
• Abundant and diverse biota
• Intermediate disturbance
• Tolerance – short-term incursions
• Migration - connectivity
• Recruitment - connectivity
• Barrage construction and
operation
• Regular disconnection of the estuary

Lower Lakes in early 2000s: an important
freshwater ecosystem of MDB
• Disproportionately high number of species
of MDB
– >130 species of plants (Holt et al. 2005; Nicol et
al. 2006)
– 100 000 birds, >30 species, Lake Albert
important breeding habitat (Kingsford and
Porter 2008)
– 22 species of fish, >half of MDB, stronghold
for 3 endangered small bodied fish
(Wedderburn & Hammer, 2003; Barnes and
Wedderburn, 2009)

Over-allocation, drought and water
level drawdown

Water level drawdown and loss of
connectivity
Jan 2007 Jan 2008

Water level drawdown and
salinisation

Loss of plants, fish and birds
• Plants
– Complete loss of extensive beds of submerged
macrophytes (Marsland and Nicol, 2009)
– Disconnection of fringing vegetation (Marsland and
Nicol, 2009)
• Fish
– Likely extinction of Yarra Pygmy Perch and large
declines in Murray Hardyhead and Southern Pygmy
Perch (Barnes and Wedderburn, 2009)
• Waterbirds
– 100,000 in 2007 to 20,000 in 2008 (Kingsford and
Porter, 2008; Kingsford and Porter, 2009)

If salinity and water level
variability are a natural feature
of the Lower Lakes,
why have they had such an
impact during the current
drought?

Early 2000s: an important ecosystem,
but vulnerable
• Important, but “vulnerable to future change” (Wedderburn & Hammer, 2003)
– Refugia for many species dependant upon submerged macrophytes for habitat
complexity
– Submerged macrophytes isolated and restricted to sheltered areas, particularly
Goolwa channel

Salt intrusions and macrophyte loss
• Freshwater macrophytes sensitive to salinity (Nielsen et al. 2003)
– 1 g/L – adverse impacts
– 4 g/L - loss
• Submerged macrophyte loss due to salinity (initially improved habitat availability during
drawdown)
→Decreased habitat complexity for small bodied fish
→ Loss of food sources for waterbirds
Salinity (g/L)

Why was macrophyte distribution limited?
1.2
Natural
• Construction and operation of Managed
Water level (mAHD)
barrages 0.8
• Loss of suitable habitat for submerged
0.4
macrophytes from main bodies of Lake
Alexandrina and Lake Albert
• Increased water depth - reduced access to 0
1950 1963 1977 1991 2004
light
Source: MDBA (Bigmod)
• Increased erosion - reduced access to light -0.4
• Lower water level variability – reduced
habitable area
• Loss of complex littoral zone and
habitat complexity
• Phytoplankton dominance

Barrage operation: constriction of
littoral zone to fringing vegetation

Habitat disconnection =
reduced resistance and
resilience

Don’t open the barrages without
sufficient freshwater flows
• Matching evaporation - resultant salinity nearly 2/3 seawater during refill
• Salt accumulates with insufficient flow
• No refuge for many freshwater organisms
• Increased siltation and dependence upon dredging

Disconnection in a
time of crisis
Ensure that temporary means temporary
Photo: Paul Harvey
Photo: Dominic Skinner Photo: Paul Harvey

Disconnection of a system that needs
connectivity to deal with future variability

So what do we do?
• Enough water to maintain as a fresh system (CSIRO, 2008)
BUT,
– 13% of years - severe drought (<1500 GL/yr) under median
climate
NEED,
– Build a system that thrives on variability
• Use the barrages as an ecological lever rather than a storage
device
• Manage at lower water levels
• Reinstate salinity and water level variability
• Create a salinity gradient (estuary) rather than a boundary
• Optimal barrage operation needs robust plans
• Match habitat preferences (salinity and water level) of biota
against inflows and barrage operation
• Engineering can be a lever, but securing adequate water will
always be the key