Transcript jay02_columbiariver_hydrology_and_salmon

A Perspective
on Hydrologic
Change in the
Columbia River
Basin
David A. Jay
OGI School of Science
and Engineering
Oregon Health &
Science University,
Portland, OR
Changes in CR Mainstem Hydrology:
Causative Factors -• Climate cycles/change
• Human intervention in
hydrologic cycle:
– flow regulation and
flood control (FCRPS)
– irrigation depletion
– tributary dams
• Loss of flood plain/marshes
• Increased fine sediment input
to tributaries
• Sediment trapping by dams
Observed Columbia River
flow at The Dalles
Impacts Important to Salmonids -• Freshets are earlier, smaller
and last longer
• Overbank flow and floodplain processes altered
• Estuarine habitats displaced
and altered
• Flow regulation constrains
habitat restoration
• Plume is smaller, timing
relative to upwelling has
changed
• Less sediment delivered to
estuary and plume
Human-induced reduction
in Columbia River flow
at The Dalles
Human Intervention in Flow Cycle -Irrigation 
Flow regulation 
Monthly Average Flows at The Dalles, 1970-99
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Flow regulation has reduced freshet flow by >40%
Irrigation and climate change have mean reduced flow by 15%
Freshet longer and peak flow earlier
Greatly increased fall-winter minimum flows
Summary of Human Impacts on
Mainstem Hydrology -• Flow regulation has decreased freshet by >40%, making it
earlier and longer in duration
• Climate change and irrigation have reduced mean CR flow
by ~15% and altered flow seasonality
• Flow regulation has reduced sediment input by ~50% and
sand by 60-70%, with effects passed onto the ecosystem
• Changes in river stage and tides constraint restoration,
e.g., by dike removal
• Future climate change will exacerbate human impacts by
increasing winter flows, decreasing spring flows
CR Plume Habitats Respond to:
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Columbia River flow and sediment input
Columbia River input of nutrients and micro-nutrients(?)
Coastal upwelling/downwelling driven by winds
Coastal currents, tides and internal tides
Spring and fall transitions in coastal circulation
Decadal climate cycles (ENSO and PDO) and long-term
changes (warming since ca. 1850)
• Changes in the coastal marine ecosystem related to climate
(zooplankton and predator populations)
Climate Cycles and
Climate Change
• Paleo-salmon research
suggests that salmon favor
cold, wet periods
• CR flow closely follows
Pacific Decadal Oscillation
(PDO)
• The 19th Century was colder
and wetter than the >1900;
native harvest had declined
relative to 1800.
• Should we expect salmon
populations to behave as
before <1900?
Kaplan PDO from SST
High Flows during Cold PDO
Smoothed Annual maximum
Columbia River flow and trend
Hydrologic Change and the Plume, 1961 vs. 1999
• June 1961 flows were >> long-term average, (20,000 m3 s-1)
• Natural flow in 1999 was 20,000 m3 s-1, but reduced by irrigation and
flow regulation to 11,000 m3 s-1
• 1999 plume covered only ~65% of area covered in 1961, fronts were
weaker, smaller in area
June 1961 Plume
June 2001 Plume
CR Plume and Hydrologic Change, Summary:
• Plume is now smaller in spring than before 1970, much
smaller than before 1900
• Plume is a highly mobile, fine-grained environment,
which is difficult to sample -- need remote sensing!
• Plume productivity interacts with coastal circulation and
upwelling in ways that are poorly understood
• PDO cycles and gradual warming of NE Pacific have
changed relationship of plume to coastal processes
• Future climate change will further decrease plume
volume in spring, may also alter upwelling
Disturbance -- Days of Overbank Flow:
Overbank levels -Historic:
Modern:
Days of Beaver Flow
• Bankfull flow level has increased from ~18,000 to 24,000
m3s-1 because of diking and revetments
• Flow regulation/irrigation prevent high flows
• Overbank flow is now rare; less large woody debris
Climate and
Habitat, 1880
vs. 1980 -• Decreased spring flows
has decreased stage,
increased tides
• Location, amount and
character of shallow
water habitat has
changed
• Interacts with diking
• Habitat restoration
efforts need to consider
this habitat displacement
Historic, with overbank flow to flood plain
Modern, no overbank flow to flood plain
Columbia Plume Frontal Properties
• Multiple fronts
move rapidly
• Physical/biological
properties change
sharply near fronts
• Eddies/upwelling
fronts also have
small scales
• Plume is a diverse,
fine-grained matrix
of habitats
• Its a difficult sampling environment!
SAR image with frontal positions superimposed, May 2001
Frontal Processes: Salinity and Turbidity
• Strong mixing seen at
front, also plunging
surface water.
• Small-scale internal
waves present
• Fronts interact with
internal tides
• Physical length scales
are ~10-200 m at fronts,
500 -5,000 m elsewhere
in plume
• Fronts are complex, hard
to sample for salmonids
Frontal study, 24 May 2001 at 1000
Frontal Processes: the Velocity Field -• Convergence across
front is >0.3 m/s
• shear along front is
>0.5 m/s
• 30 sec averaging on
300 kHz ADCP
minimizes shear and
convergence through
averaging.
• Depth is ~40-42 m
Normal to front is
oriented 340° T. Note
~southward flow at
depth.
Frontal study, 24 May 2001 at 1000; velocities relative
to stationary front. Note different vertical scale from salinity plot.
Future Climate Change Effects -•
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Warmer temperatures likely; precipitation may increase
Warmer winters will bring lower snowpacks
Spring freshets will be smaller and earlier
This will exacerbate larger regulation/irrigation effects
Spring freshets related to spring snow will disappear
Summer river temperatures will be higher
Winter freshets related to Western Sub-basin snowpack
will disappear
• Winter freshets related to Interior Sub-basin snowpack
may increase in intensity and frequency
• Lower sediment transport and overbank flow rates