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 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 -- 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, Flow regulation  Irrigation 

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: 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 19 th Century was colder and wetter than the >1900; native harvest had declined relative to 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 m 3 s -1 ) Natural flow in 1999 was 20,000 m 3 s -1, but reduced by irrigation and flow regulation to 11,000 m 3 s 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 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: Bankfull flow level has increased from ~18,000 to 24,000 m 3 s -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 and Habitat, 1880 vs 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 samp- ling 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 ~ m at fronts, ,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 -- 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