Environmental flow objectives in a working river

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Environmental flow objectives in a working river
Terry Hillman
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New South Wales
Murrumbidgee
S.A.
Murray
Victoria
Melbourne
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Streamflow models
Murray Bigmod (MDBC), Murrumbidgee IQQM (DIPNR)
Daily time-steps, 1901-2000
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Scenarios
CURRENT. Assuming regulating structures
and water diversions existing currently were
in place and operational throughout the
modelled period. NATURAL. Assuming no
structures or diversions existed throughout the
modelled period
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New South Wales
Murrumbidgee
S.A.
Murray
Victoria
Melbourne
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New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced s/t flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced s/t flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
8
New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperatures 4.
Reduced s/t flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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Mean Monthly Flows at Albury (GL/month)
800
Natural
Current
600
400
200











Jul
Sep
Nov
Jan
Mar
May
10
Mean Monthly Flows at Euston (GL/month)
2000
1600
Natural
1200
Flow
600
Current
400
Jul Aug Sep Oct Nov
Dec Jan Feb Mar Apr May
Jun

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New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced s/t flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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Mitta Mitta River at Tallandoon Weekly Water
Temperature
July 1978 June 1980
July 1990 June 1992
Jun
Dec
Jun
Dec
Jun
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New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced s/t flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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Cumulative frequency distribution of dailyflow
changes (modelled) at Albury
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New South Wales
S.A.
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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High-Flow Event (HFE)
Occurs (commences) in August/September
Water reaches the majority of floodplain
wetlands (plus low-lying terrestrial
floodplain areas)
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DURATION DEPENDENT
EVENT DEPENDENT
Stimulate native fish population
Fish Breeding Preparation (physiol.)
Complete to larval stage
Fish Commence Migration
Inundate floodplain Plants
Kill invasive species Structure plant
community Support seedlings Flowering, seed
production
- Trigger germination- Move litter to channel
Fill floodplain waterbodies
- Trigger production sequence- Water bird
mating
Provide products to river channel (C,
bacteria, microinvertebrates)
Food supplySupport to fledging.
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New South Wales
10000 ML/day
b
a
S.A.
32500 ML/day
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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Rapid cycling of Nutrients and carbon Large,
active microbialcommunity Large, diverse
Zooplankton comm.
Flow DiluteDiverse habitats Endemic
Inverts. Large Fish
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Water for wetland and Vegetation
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Day 0 Dilution by river water of carbon,
nutrients, bacteria and zooplankton
Day 1 Buildup of carbon (dis. part.)
from wetted area.
Day 1-4 Rapid increase in bacterial
community (reproduction, emergence from
sediment) in response to carbon
Day 5-15 Rapid increase in zooplankton
community
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Day 1, 6, 12?
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Events lasting gt 11 days
Events lasting gt6 days
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Events of any duration
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New South Wales
10000 ML/day
b
a
S.A.
32500 ML/day
1. Physical Barriers 2. Seasonal Flow
inversion. 3. Reduced Summer Temperature 4.
Reduced flow variability 5. Changed frequency
ofsignificant events
Victoria
Melbourne
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1900
1920
1940
1960
1980
2000
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Loss of High-Flow Events can be benign attimes
yet catastrophic under extreme circumstances
Remedial responses can include Engineering
modifications Allocation and delivery of
water Mimicking or reinforcing a natural event
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Some Conclusions

• Simple reduction in irrigation allocation is
  impractical
• Ecologically damaging aspects of water
  resourcemanagement (the human footprint) require
  a varietyof remedial responses Some are
  irremediable Some can be (partly) corrected
  through engineering modifications Some
  require a specific allocation (return) of
  water.
• Return of water to the ecosystem must be
  strategicand based on an understanding of the
  ecosystem.

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