The Darling River in drought: where does all the water go and how can isotopes help us find out?

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The Darling River in droughtwhere 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
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Catchment area 650,000 km2
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Climate context

• Avg Rainfall 500 mm/yr
• lt200mm/yr to gt1200mm/yr
• Avg Potential E 2000 mm/yr

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Past and present river flows
OBSERVED FLOWS
Natural 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
PAST FLOWS MODELLED FOR CURRENT DIVERSION
CONDITIONS
MEDIAN FLOW MORE THAN HALVED BY DIVERSIONS
5-10 FOLD INCREASE IN DIVERSIONS SINCE 1980s
Climate change and variability may affect water
supply and demand but human water use and
catchment management have a very big impact!
Current median annual flow
DNR NSW Drought Analysis 2006
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Water 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 lt5m)
• Summer temps high 30s to mid 40ºC leading to
  high evaporation rates

Thanks to Google Earth
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Saline groundwater at Glen Villa weir 19A
FISH KILL AT GLEN VILLA
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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 18O2005.2 ppm, 2H155.75 ppm
expressed as ratio of the standard VSMOW in per
mille
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So how do isotope ratios change in the
hydrological cycle?
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Darling Basin stable isotopes evaporation

• Extreme evaporative enrichment in Barwon-Darling,
  tributaries and reservoirs
• The degree of enrichment can be used to determine
  how much water has evaporated

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Imagine the river is like a cup of water left out
in the sun in a river its not so easy to
measure how much water evaporates but using
isotopes we can
GMWL ?D 8?18O10
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Water sampling along the Darling River
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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 flourishWHAT EFFECT WILL CLIMATE
CHANGE HAVE?
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bute to the planet, have fun, visit great places!
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