Presented by Julian D. Olden at the Third International Symposium on Riverine Landscapes (2007)

1. Riverine Thermal Regimes
An Integral Component of Environmental Flows
Julian D. Olden
School of Aquatic and Fishery Sciences
University of Washington

2. Ecologically Sustainable
Water Management
Meeting the fresh water
demands of a growing human
population while ensuring
ecosystem integrity has
emerged as one of the world’s
primary resource issues.
Shifting focus from humans as
exploiters of the environment
to a world where riverine
systems are legitimate “users”
of fresh water.

3. The Science of Environmental Flows
Scientists are becoming increasingly engaged in the development
of environmental flow recommendations.
An environmental flow is can be defined as the
quantity, quality and timing of water flows
required to maintain the components,
functions, processes and resilience of aquatic
systems which provide goods and services that
are valued by society.
Efforts in environmental flow research have thus
far have focused primarily on water quantity,
whereas issues involving water quality, such as
water temperature, have received little
consideration.

4. Why has temperature been overlooked
in environmental flow science?
Society is largely unaware of the ecological importance of a
river’s thermal regime for freshwater biodiversity and
ecosystem function.
Scientists have their hands full with understanding how
freshwater ecosystems respond to hydrologic modification
and how best to use this information to inform the
science of environmental flows.
The impacts of river regulation on
downstream thermal regimes are
considered to be small compared to the
potential for flow alteration.

5. Objectives
The scientific community must broaden its perspective on
ecologically sustainable water management to include
aspects of the thermal regime in the science of
environmental flows.
1. Review the concept of the natural thermal regime.
2. Illustrate how river regulation has modified thermal
regimes and discuss the ecological impacts.
3. Challenge us to expand our perspective on environmental
flows to include the management of thermal regimes for
riverine ecosystem integrity.

6. Water Temperature
Stream temperature
is dependent on:
Energy budget
- the amount of heat
energy added or loss
to the channel.
Thermal capacity
- the volume of water
to be heated or
cooled.

7. The Natural Thermal Regime
Stream temperatures show marked annual and diurnal fluctuations
in response to seasonal and daily rhythms in the flux of heat
energy gained and lost by a stream and the volume and source of
runoff contributing to discharge.
Bullpasture River, Virginia, USA

8. The natural thermal regime can be discomposed into its
components of magnitude, frequency, duration, timing, and rate
of change, and be summarized using statistics that describe the
central tendency and variability in distributions of water
temperatures.
Mean annual T and CV
Predictability/Constancy
Magnitude
Mean monthly T and CV
Frequency
1-/3-/7-/30-day maxima T
1-/3-/7-/30-day minima T
Descriptors of the Thermal Regime Duration
High pulse count and duration
Low pulse count and duration
Timing
Maximum and minimum T
Rate of Change
Rise and fall rates
# reversals

9. Ecological Importance of Temperature
Water temperature directly influences the metabolic rates,
physiology, and life-history traits of aquatic species and
helps determine rates of important ecological processes.
Freshwater fishes and aquatic macroinvertebrates utilize a
diverse array of thermal habitats to meet their specific
temperature requirements for survival, growth and
reproduction.
Components of the thermal regime have different ecological
significance.

10. Thermal Modification in
Lotic Ecosystems
Human activities may strongly alter spatial and temporal
patterns in water temperatures by modifying the energy
budget and thermal capacity of the river.
Sources of “warmwater pollution”
 Forestry, agriculture, and urbanization
• Industrial effluents
• Irrigation diversions

11. Coldwater Pollution below Dams
River regulation by dams can greatly modify water
temperatures depending on their mode of operation and
specific mechanism of water release.
Large dams directly modify thermal
regimes by releasing water that
greatly differs in temperature
from natural conditions (Storage
Effect).
By changing the volume of water,
dams also influence temperature
by affecting energy fluxes
(Regulation Effect).
Arthur Rylah Institute

12. Keepit Dam - Namoi River, Australia
 Annual maximum daily temperature was 5.0°C lower and
occurred 3 weeks later compared to pre-dam conditions.
 Magnitude of thermal alteration decreased with distance
downstream from dam.
Preece and Jones (2002)

13. Blowering Dam – Tumut River, Australia
 Reductions in natural summer temperatures of 13.0°C to
16.0°C.
 Contributes to coldwater pollution for 80 river km below
the dam and >200 km in the Murrumbidgee River.
Lugg (1999), Preece (2004)

14. Vilui Dam - Lena River, Siberia
 Post-dam temperatures were 2-5°C higher in early-
summer and 2-3°C lower in mid-summer.
Lui et al. (2005)

15. Flaming Gorge Dam – Green River, USA
 Summer temperatures (June-Aug) were, on average,
12.0°C lower compared to pre-dam conditions.
 Annual maximum daily temperature was 14.0°C lower and
its timing shifted from end-July to mid-December.
Vinson (2001)

16. Gathright Dam – Jackson River, USA
 Summer temperatures (June-Aug) were, on average,
6.0°C lower compared to pre-dam conditions.
 Annual maximum daily temperature was 8.0°C lower.
Olden et al. (in review)

17. Ecological Implications of
Coldwater Pollution
Cold water releases can have lethal and sub-lethal effects.
Water temperatures below tolerance limits result in species
extirpation, and sub-lethal impacts include a slowing of
physiological processes such as reproduction and growth.
Lower spring/summer water temperatures compromise the structure
and life-history of stream macroinvertebrate assemblages, and
decrease the survival of egg, larval and adult fishes.
Delayed timing of peak spring temperatures disrupt critical cues for
initiating fish spawning and insect reproduction and emergence.

18. Thermal regimes do not satisfy the
spawning requirements of native fishes
Pre-dam
Post-dam
Gathright Dam, Jackson River, USA

19. Five major challenges to developing
comprehensive environmental flow
assessments that incorporate the
critical temperature requirements of
riverine ecosystems.

20. CHALLENGE 1
Improve our understanding of spatiotemporal
variability in riverine thermal regimes
 Previous attempts to explore similarities in thermal
regimes among rivers and develop formal classification
systems have been limited.
 Quantifying thermal variability in undeveloped rivers is
essential for establishing regional benchmarks needed to
successful incorporating water temperature into
environmental flow management.
 The paucity of continuous water temperature data
represents a significant information gap, requiring a
greater dependence on statistical modeling.

21. CHALLENGE 2
Quantify the degree to which dams alter
riverine thermal regimes
 In general, the scientific community has inadequately
quantified the magnitude and geographic extent of dam-
induced thermal alteration.
 Formal investigations of how dams are altering the various
facets of the thermal regime are needed, including
ecologically-relevant components of magnitude, frequency,
duration, timing and rate of change in temperature events.
 This research is critical for mounting a convincing
argument that temperature should play a significant role in
the science and management of environmental flows.

22. Flaming Gorge Dam – Green River, USA
 Green River is the largest tributary
of the Colorado River.
 Flaming Gorge dam was constructed
in 1962 for hydroelectric power and
flood control.

23. Degree of Thermal Alteration
Daily water temperature records
• Pre-dam: 1958-1962
• Post-dam: 1963-1977
Mean annual temperature
decreased 2.5°C from
8.8°C to 6.3°C.
Annual variability in water
temperatures (CV) decreased
from 89% to 34%.
Thermal regimes were >2 times
more predictable in post-dam
years.

25. Olden and Naiman (in prep)

26. Why has temperature been overlooked
in environmental flow science?
Society is largely unaware of the ecological importance of a
river’s thermal regime for freshwater biodiversity and
ecosystem function.
Scientists have their hands full with understanding how
freshwater ecosystems respond to hydrologic modification
and how best to use this information to inform the
science of environmental flows.
The effects of river regulation on downstream
thermal regimes are considered to be
smaller compared to the potential for
flow alteration.

27. Thermal vs. Hydrologic Alteration
↑Thermal Alteration
1-/3-/7-/30-day minimum
Dec (Winter)
Jan (Winter)
Feb (Winter)
90-day minimum
Nov (Winter)
Mar (Winter)
↑Hydrologic
Alteration
Date of maximum July - Oct (Summer)
Date of minimum
Rise and fall rates
Lower pulse count
Olden and Naiman (in prep)

28. CHALLENGE 2 …
• Data limitation is a significant problem.
• “Desk-top” assessments have been used
to identify and rank large dams based
on potential to cause coldwater
pollution according to intake depth,
discharge, storage, etc …
Queensland: 18 dams (Brennan, in prep)
NSW: 9 dams (Preece 2004)
Victoria: 24 dams (Ryan et al. 2001)
DIPNR (2004)

29. CHALLENGE 3
Quantify the ecological consequences of
altered thermal regimes
• Systematic assessments of
the relationship between
biological condition and
the degree of thermal
alteration are needed.
 Place the ecological
impacts of thermal
pollution in the context of
broader ecological
disturbances associated
with dams.

30. CHALLENGE 4
Demonstrate the availability and success of
thermal pollution remediation strategies
Various mitigation measures are available:
• Multi-level outlet structures
• Artificial destratification (large propellers that pump cold
bottom water toward the surface)
• Trunnions (piping system that draw water from different
levels in the water column)
• Surface pumps (large propellers that pump warm surface
water into existing outlets)
• Draft tube mixers
• Submerged curtains (large curtains extending upwards from
the bottom of the reservoir forcing all the release water to
originate from the surface)
• Stilling basins

31. Thermal Restoration below
Flaming Gorge Dam – Green River, USA
Daily water temperature records
Pre-dam: 1958-1962
Post-restoration: 1978-2006
Mean annual temperature
decreased 0.3°C from
8.8°C to 8.5°C.
Annual variability in water
temperatures (CV) decreased
from 89% to 42%.
Thermal regimes were >2 times
more predictable in post-dam
years.

32. Post-dam (1963-1977) Post-restoration (1978-2006)

33. CHALLENGE 5
Develop a multi-faceted perspective on
environmental flows
 Understand the relationships between flow alteration,
thermal alteration, (other dam-induced drivers of
environmental change), and the integrity of riverine
ecosystems.
 Develop conceptual models and assess different
environmental flow strategies that include prescriptions for
both flow and temperature regimes.

34. B
A
A. Thermal restoration below Flaming Gorge Dam (Vinson 2001)
B. Flow restoration below Clanwilliam Dam (King et al. 1998)

36. Take Home Message
• Dams can substantially modify riverine thermal regimes,
which can result in significant ecological impacts.
• The degree of thermal alteration below dams may greatly
exceed the level of flow alteration.
• The benefits of environment flows may not be fully
realized unless critical aspects of the thermal regime are
also considered.
• Incorporating aspects of water quality into environmental
flow science and management represents a necessary step
forward in ecologically sustainable water management.