Instream flow assessment in New Zealand

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Instream flow assessment in New Zealand
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Flow assessment framework
Evaluate for changes in flow
Morphology
Water quality
Velocity/depth
Methods and parameters
DO Temperature NH3
Hydraulic geometry 2d models Stage/Discharge Water
surface profile
Biological evaluation
Water quality suitability
Habitat suitability
Flow assessment based on flow response curves of
biological indicators
Flow regime requirements
Methods
Flushing flow analysis (shear stress) Fluctuating
flow habitat analysis Sediment deposition
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Instream habitat

• Habitat suitability is a widely used concept
  e.g., angling and hunting
• No suitable habitat - no fishSuitable habitat -
  maybe..

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Three basic life requirements for fish and
benthic invertebrates that live in flowing water

• Velocity
• Depth
• Cover

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New Zealand adult brown trout (Hayes Jowett
1994)
1.0
1.0
0.8
0.8
0.6
0.6
Suitability
Suitability
0.4
0.4
0.2
0.2
0.0
0.0
0.0
0.3
0.6
0.9
1.2
1.5
0.0
0.4
0.8
1.2
1.6
2.0
Depth (m)
Velocity(m/s)
Adult brown trout (Raleigh et al. 1984)
1.0
1.0
0.8
0.8
0.6
0.6
Suitability
Suitability
0.4
0.4
0.2
0.2
0.0
0.0
0.0
0.3
0.6
0.9
1.2
1.5
0.0
0.4
0.8
1.2
1.6
2.0
Depth (m)
Velocity(m/s)
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Prediction of depth and velocity
Level at 11 m3/s
1.00
0.25
-0.50
Depth (m)
Level at 5.3 m3/s
-1.25
2.0
-2.00
1.6
11 m3/s
1.2
Velocity (m/s)
5.3 m3/s
0.8
0.4
0.0
0
4
8
12
16
20
Offset (m)
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Habitat quality across river
8
Usable habitat summed over reach for each flow
10
8
Weighted usable area (m2/m)
6
4
2
0
0
5
10
15
20
25
Discharge (m3/s)
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NZ case studies
5
6
4
3
1
2
10

• River flows are affected by
• Hydroelectric diversion,
• Hydroelectric flow control, or
• Irrigation diversion
• Studies between 1979 and 2001
• Trout, benthic invertebrate, and native fish goals

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For each project

1. Description of river and flows
2. Habitat analysis and flow recommendation
3. Before and after photographs
4. Biological response

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Waiau RiverHydroelectric diversion

• Lake fed river - natural mean flow 450 m3/s
• River diverted for hydropower generation in 1976
• Minimum flow of 0.3 m3/s since dam construction

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Goal Trout and food production
Winter flow
Summer flow
30
Adult brown trout
25
20
Food production
WUA (m2/m)
15
10
5
0
0
5
10
15
20
25
30
Discharge (m3/s)

• Maximum habitat at gt15 m3/s
• Sharp drop as flow goes below 10 m3/s

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Minimum flow of 12-16 m3/s since August 1997
Before flow about 1 m3/s
After flow about 16 m3/s
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Waiau River
Before
After minimum flow
1000
100
Flow (m3/s)
10
1
1 year
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Numbers of trout (gt20 cm)
250
Before
After minimum flow
200
150
Brown and rainbow trout per km
100
50
0
1996
1997
1998
1999
2000
2001
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Brown and rainbow trout densities ranked
nationally
350
300
Waiau River
250
After
200
Trout (gt 20 cm) per km
Before
150
100
50
0
River (300 reaches in descending order)
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Monowai RiverControlled flow to hydroelectric
plant

• Lake fed river - mean flow 13.8 m3/s
• Dam at lake controls flow to downstream power
  station
• Minimum flow of near zero, usually each night

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Goal Invertebrate abundance and diversity
Maximum
Sharp drop
15
Food production
10
WUA (m2/m)
5
0
0
2
4
6
8
10
Discharge (m3/s)

• Maximum habitat at 5-7 m3/s
• Sharp drop as flow go below 3 m3/s

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Minimum flow since July 1994
Before
After minimum flow
20
15
10
Flow (m3/s)
5
0
1-JAN-95
1-JUL-95
1-JAN-92
1-JUL-92
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Invertebrate abundance and diversity
After minimum flow increased to 6 m3 s-1
Before
25
1000
20
800
Taxon richness
15
600
Density (no m-2)
Taxon richness (no per sample)
10
400
Density
5
200
0
0
1991
1992
1993
1994
1995
1996
1997
1998

• Invertebrate abundance doubled
• Number of species doubled

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Ohau RiverHydroelectric diversion

• Lake fed river - mean flow 80 m3/s
• Flow diverted for hydropower in 1979
• Minimum flow of near zero

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Goal High quality brown trout fishery
Maximum
20
Food production
15
WUA (m2/m)
10
Adult brown trout
5
0
0
5
10
15
Discharge (m3/s)
Habitat analysis indicated excellent adult trout
and food producing habitat at 10 m3/s
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Minimum flow of 10-14 m3/s since 1994
Before Flow lt 1 m3/s
After Flow 10 m3/s
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• Failed to meet expectations
• Trout present, but not many
• Reasons unknown
• Food ?
• Recruitment?
• Flow too high?

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Tekapo RiverHydroelectric diversion

• Lake fed river - mean flow 90 m3/s
• Lake flow diverted in 1978 leaving 10 m3/s from
  tributaries

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Goal High quality trout fishery
Habitat begins to drop sharply
30
Food production
/m)
20
2
WUA (m
10
Trout spawning
0
0
5
10
15
20
3
Discharge (m
/s)

• Excellent adult trout spawning and food producing
  habitat at gt10 m3/s

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Just below dam Zero flow
45 km downstream Flow 10 m3/s
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Tekapo River

• Before diversion (flow 90 m3/s)
• Not mentioned in angling surveys
• Some trout spawning
• After diversion (flow c. 10 m3/s)
• Up to 240 brown and rainbow trout (gt 20 cm) per
  km
• More than 200 juvenile brown and rainbow trout
  per km

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Brown and rainbow trout densities ranked
nationally
350
300
250
After
200
Before?
Brown and rainbow trout (gt 20 cm) per km
150
100
50
0
River (300 reaches)
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Moawhango RiverHydroelectric diversion

• Natural mean flow 9.3 m3/s
• In 1991, all water was diverted to another river
  system

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Goal benthic invertebrate community composition
Sharp drop
Maximum
15
12
WUA (m2/m)
9
6
3
0
0
1
2
3
4
5
Discharge (m3/s)

• Sharp reduction at flows lt 0.8 m3/s

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Minimum flow of 0.6 m3/s since June 2000
Before 0.06 m3/s
After 0.52 m3/s
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Desirable species
Undesirable species
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Before (1997)
30
After (2002)
Percentage of total
20
10
0
Elmidae
Lymnaea
Tanytarsus
Ostracods
Deleatidium
Oligochaeta
Zelandoperla
Aoteapsyche
Maoridiamesa
Orthocladiinae
Potamopyrgus
Pycnocentrodes
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Waipara RiverDiversion for irrigation

• Small gravel-bed river
• Mean flow 2.5 m3/s

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Goal maintain native fish population
Sharp drop
8
Common river galaxias
6
Longfin eel (lt300 mm)
Upland bully
WUA (m2/m)
4
Torrentfish
Bluegill bully
Common bully
2
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Discharge (m3/s)
Habitat for a species with intermediate
velocity preference begins to decline sharply at
0.12 m3/s
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(No Transcript)
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Effect on Fish Population
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Conclusion

• This is all the NZ data on biological response to
  flow changes
• Flow assessments were based on habitat
  requirements
• 5 out of 6 were successful
• The outcomes dont support commonly held views
  that more flow is better and that all aspects of
  a natural flow regime are important

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Thank you