A Perspective A Perspective on Hydrologic on Hydrologic Change in the Change in the Columbia River Columbia River BasinBasin

David A. JayOGI School of Science and EngineeringOregon Health & Science University, Portland, OR

Changes in CR Mainstem Hydrology:Changes in CR Mainstem Hydrology:Causative Factors --

• Climate cycles/change

• Human intervention in hydrologic cycle:

– flow regulation andflood 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 --Impacts Important to Salmonids --• Freshets are earlier, smaller

and last longer

• Overbank flow and flood-plain 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 --Human Intervention in Flow Cycle --

• 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

Monthly Average Flows at The Dalles, 1970-99

Flow regulation

Irrigation

Summary of Human Impacts on Summary of Human Impacts on Mainstem Hydrology --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:CR Plume Habitats Respond to:• 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 Cycles and Climate ChangeClimate 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

Smoothed Annual maximum Columbia River flow and trend

High Flows during Cold PDO

• 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

Hydrologic Change and the Plume, 1961 vs. 1999Hydrologic Change and the Plume, 1961 vs. 1999

June 2001 Plume

CR Plume and Hydrologic Change, Summary: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:Disturbance -- Days of Overbank 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

Overbank levels --Historic: Modern:

Days of Beaver Flow

Climate andClimate andHabitat, 1880 Habitat, 1880 vs. 1980 --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 PropertiesColumbia Plume Frontal Properties• Multiple fronts

move rapidly

• Physical/biologicalproperties changesharply near fronts

• Eddies/upwelling fronts also have small scales

• Plume is a diverse,fine-grained matrixof habitats

• Its a difficult samp- ling environment!

SAR image with frontal positions superimposed, May 2001

Frontal Processes: Salinity and TurbidityFrontal 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 --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 --Future Climate Change Effects --• 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