Transcript The Darling River in drought

The Darling River in drought:
where does all the water go and
how can isotopes help us find out?
Cath Hughes
With input from Dioni Cendon, John
Gibson, Stuart Hankin, Suzanne Hollins,
Karina Meredith and David Stone
& the invaluable collaboration of the
NSW Dept of Water and Energy
FIELD ASSISTANT AT TILPA PUB
Catchment area 650,000 km2
Climate context
Murray Darling Basin Annual Rainfall
Avg Rainfall = 500 mm/yr
<200mm/yr to >1200mm/yr
Avg Potential E = 2000 mm/yr
Recent drought years 2001-6
similar rainfall to first half of
20th century – so why is this
drought so severe?
Murray Darling Basin Annual Rainfall Anomaly (base 1961-90)
Higher temperatures and
potential evaporation
Murray Darling Basin Annual Mean T Anomaly (base 1961-90)
Increased water diversions
D arling River @ W ilcannia
Observed Flow sFLOWS
(Filled)
OBSERVED
Past and present
river flows
01/07/1914 to 30/06/2006
Flow
16000
14000
– – – Natural median annual flow
12000
10000
GL /Y R
River flow modelling from the
NSW Dept of Water and
Energy shows the effect of
dams, weirs and pumping for
irrigation for last 90 years
8000
6000
4000
2000
0
2000
1990
1980
1970
1960
1950
1940
date:15/11/06 tim e:14:54:13.76
D arling River @ W ilcannia
PAST FLOWS MODELLED
FOR CURRENT DIVERSION
Current Conditions IQQM Simulated
CONDITIONS
01/07/1922 to 30/06/2006
14000
12000
GL /Y R
10000
MEDIAN FLOW
MORE THAN
HALVED BY
DIVERSIONS
Flow
5-10 FOLD INCREASE IN
DIVERSIONS SINCE 1980’s
– – – Current median annual flow
8000
6000
4000
2000
0
2000
1990
Y ears
1980
1970
DNR NSW Drought Analysis 2006
1960
1950
1940
1930
Climate change and
variability may affect water
supply and demand but
human water use and
catchment management have
a very big impact!
1930
1920
Y ears
If all the diversions now in place
were there during 1920’s to the
1940’s the flow in the river
would have been halved
date:16/11/06 tim e:10:15:02.60
Cotton irrigation near Bourke
• 1650 GL/year water use from catchment
• 310 GL/year water use from BarwonDarling River reaches in this study
• 300 GL storage capacity in shallow dams
(max depth <5m)
• Summer temps high 30’s to mid 40ºC
leading to high evaporation rates
Cotton irrigation storage dam
Thanks to Google Earth
Water diversions
Saline groundwater at Glen Villa weir 19A
Glen Villa Weir - EC and river level
14000
8
12000
7
6
10000
5
8000
4
6000
3
Jul 05
0
Jan 05
0
Jul 04
1
Jan 04
2000
Jul 03
2
Jul 02
4000
River level (m)
9
EC
Jan 03
FISH KILL AT GLEN VILLA
Stage
Jan 02
EC (m S/cm)
16000
Where do isotopes come into the equation?
Isotopes have the same atomic number but different
numbers of neutrons in the nucleus – they can be
stable or radioactive - natural or anthropogenic.
In some water molecules either a 1H or 16O atom is
replaced by its ‘heavier’ cousin – 2H or 18O.
Heavy or ‘enriched’ molecules condense or rain out
quicker and evaporate slower so they can be used
to study hydrological processes.
Deuterium or 2H atoms were formed during the
BIG BANG!
Abundance 18O=2005.2 ppm, 2H=155.75 ppm –
expressed as ratio of the standard VSMOW in per mille ‰
So how do isotope ratios change in the
hydrological cycle?
Darling Basin stable
isotopes & evaporation
GMWL
80
60
40
LEL
d H = 4.89d O - 5.05
2
18
R2 = 0.97
0
2
d H (‰)
20
-20
GMWL
Barwon-Darling
Barwon-Darling
Tributaries
Local Evaporation Line
Menindee Lakes
Murray-Murrumbidgee
Glen Villa groundwater
Local Evaporation Line
-40
-60
• Extreme evaporative enrichment
in Barwon-Darling, tributaries
and reservoirs
• The degree of enrichment can
be used to determine how much
water has evaporated
-80
-10
-5
0
5
10
15
d 18O (‰ )
(Gibson et al. 2002)
60
40
0
0.2
0.3
0.4
0.5
0.6
15
15000
10
5
LEL
2
d H =50004.88d 18O - 5.13
10000
0
-5
2
R
1/7/02 = 0.97
0.8
-20
isotope values increase between
floods at Wilcannia
20000
0
2
d H (‰)
20
Evaporation can
be seen in one
place in time…
d18 O (‰)
80
Daily discharge (ML)
Imagine the river GMWL
is like a cup of
d
D = 8d 18O+10
water left out in
the sun – in a
river it’s not so
easy to measure
how much water
evaporates but
using isotopes
we can…
0.7
-10
1/7/03
1/7/04
1/7/05
… or over distance as
we travel down river
0.9
1.0
-40
15
Aug 03
Jan 04
10
18
d O (per mille)
-60
-80
-10
-5
0
5
0
5
-5
d 18O (‰)
10
15
flood front
-10
2000
1800
1600
1400
1200
1000
Distance upstream (km)
800
600
400
200
0
Water sampling along the Darling River
The Darling River is dying of thirst…
Big dams and water extraction for irrigation of cotton and other crops
are taking the water the river needs. Weirs along the river allow water to
evaporate, contaminants to concentrate and algal blooms to flourish…
WHAT EFFECT WILL CLIMATE CHANGE HAVE?
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