The Darling River in drought:The Darling River in drought:where does all the water go and where does all the water go and

how can isotopes help us find out?how can isotopes help us find out?

Cath HughesCath HughesWith input from Dioni Cendon, John With input from Dioni Cendon, John

Gibson, Stuart Hankin, Suzanne Hollins, Gibson, Stuart Hankin, Suzanne Hollins, Karina Meredith and David StoneKarina Meredith and David Stone

& the invaluable collaboration of the & the invaluable collaboration of the NSW Dept of Water and EnergyNSW Dept of Water and Energy

FIELD ASSISTANT AT TILPA PUB

Catchment area 650,000 km2

Climate contextClimate context

Avg Rainfall = 500 mm/yr<200mm/yr to >1200mm/yr Avg Potential E = 2000 mm/yr

Murray Darling Basin Annual Rainfall

Murray Darling Basin Annual Rainfall Anomaly (base 1961-90)

Recent drought years 2001-6 similar rainfall to first half of 20th century – so why is this drought so severe?

Murray Darling Basin Annual Mean T Anomaly (base 1961-90)

Higher temperatures and potential evaporation

Increased water diversions

Past and present Past and present river flowsriver flows

d at e : 1 5 / 1 1 / 0 6 t i m e: 1 4 : 5 4 : 1 3 .7 6

D ar l i n g R i v er @ W i l c an n i a O b ser v ed F l o w s ( F i l l ed )

0 1 /0 7 /1 9 1 4 t o 3 0 /0 6 /2 0 0 6

0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

1 4 0 0 0

1 6 0 0 0

G

L/Y

R

Y ear s

1920

1930

1940

1950

1960

1970

1980

1990

2000F l o w

d a t e : 1 6 / 1 1 / 0 6 t i m e: 1 0 : 1 5 : 0 2 .6 0

D ar l i n g R i v er @ W i l c an n i a C u r r en t C o n d i t i o n s I Q Q M S i m u l at ed

0 1 /0 7 /1 9 2 2 t o 3 0 / 0 6 /2 0 0 6

0

2 0 0 0

4 0 0 0

6 0 0 0

8 0 0 0

1 0 0 0 0

1 2 0 0 0

1 4 0 0 0

G

L/Y

R

Y ear s

1930

1940

1950

1960

1970

1980

1990

2000

F l o w

DNR NSW Drought Analysis 2006

OBSERVED FLOWS

PAST FLOWS MODELLED FOR CURRENT DIVERSION CONDITIONS

MEDIAN FLOW MORE THAN HALVED BY DIVERSIONS

5-10 FOLD INCREASE IN DIVERSIONS SINCE 1980’s

– – – Natural median annual flow

– – – Current median annual flow

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

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

Climate change and variability may affect water supply and demand but human water use and catchment management have a very big impact!

Cotton irrigation near Bourke

Water diversionsWater diversions

• 1650 GL/year water use from catchment• 310 GL/year water use from Barwon-

Darling 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

Th

an

ks

to

Go

og

le E

art

h

Cotton irrigation storage dam

Glen Villa Weir - EC and river level

0

2000

4000

6000

8000

10000

12000

14000

16000

Jan

02

Jul 0

2

Jan

03

Jul 0

3

Jan

04

Jul 0

4

Jan

05

Jul 0

5

EC

(m

S/c

m)

0

1

2

3

4

5

6

7

8

9

Riv

er

lev

el (

m)

Stage EC

Saline groundwater at Glen Villa weir 19ASaline groundwater at Glen Villa weir 19A

FISH KILL AT GLEN VILLA

Where do isotopes come into the equation?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 theBIG 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 So how do isotope ratios change in the hydrological cycle?hydrological cycle?

(Gibson et al. 2002)

LELd 2H = 4.89d 18O - 5.05

R2 = 0.97

-80

-60

-40

-20

0

20

40

60

80

-10 -5 0 5 10 15

d18O (‰)

d2H

(‰

)

GMWL

Barwon-DarlingLocal Evaporation Line

GMWL

-80

-60

-40

-20

0

20

40

60

80

-10 -5 0 5 10 15

d18O (‰)

d2H

(‰

)

GMWLBarwon-DarlingTributariesMenindee LakesMurray-MurrumbidgeeGlen Villa groundwaterLocal Evaporation Line

GMWL Darling Basin stable Darling Basin stable isotopes & evaporationisotopes & evaporation

• Extreme evaporative enrichment in Barwon-Darling, tributaries and reservoirs

• The degree of enrichment can be used to determine how much water has evaporated

GM

WL dD

= 8d1

8 O+1

01.0

0.9

0.7

0.5

0.3

0.6

0.4

0.2

0.8

Imagine the river is like a cup of 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…

Evaporation can be seen in one place in time…

d18

O (

‰)

0

5000

10000

15000

20000

1/7/02 1/7/03 1/7/04 1/7/05

Da

ily d

isc

ha

rge

(M

L)

-10

-5

0

5

10

15

isotope values increase between floods at Wilcannia

… or over distance as we travel down river

flood front

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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