U.S. Department of the InteriorU.S. Geological Survey

Processes and Landforms of the Willamette River and Floodplain:

Current Understanding and Information Needs

Rose Wallick

Jim O’Connor

Krista Jones

Mackenzie Keith

Charles Cannon

Dave Hulse

Stan Gregory

Introduction

19951850

Upper Willamette Historical Channel Change

• Previous studies documented historical changes and created rich datasets

• Much is still unknown about “modern” channel processes

Map sources: Willamette Planning Atlas; Hulse and others 2001

Emerging Management Challenges for the Willamette Floodplain

What are reasonable targets for restoration strategies?

Revetment

What happens if…Revetments are modified? Environmental flows are implemented?Multiple strategies are implemented?

Photo courtesy of Freshwaters Illustrated

Geomorphic Processes Shaping Willamette Valley Floodplains

Purpose and Approach

Overarching goal:

Build a roadmap towards better understanding of geomorphic processes in Willamette Valley

Study Approach: Describe floodplain landforms and processes Explain our current understanding Identify major knowledge gaps Outline future studies

Study Area

Alluvial, gravel-bed portion of Willamette River and major tributaries

Landforms and geomorphic processes broadly similar

Interconnected system of landscapes and ecosystems

Willamette Geomorphic Floodplain

High Channel Complexity

Upper Willamette upstream of Harrisburg

Comparison of Landforms along Willamette River

Side channels

Gravel bars

Low Channel Complexity

Middle Willamette near Albany

Side channel

Stable, vegetated bar

Aerial photographs from 2011

High Channel Complexity

Comparison of Landforms along Tributaries

Lower North Santiam near Wiseman Island

Side channels

Active bars

Low Channel Complexity

Middle Fork near Jasper State Park

Side channels

Stable, vegetated bars

Aerial photographs from 2011

Diversity of Channel Morphologies Reflects Differences in Geomorphic Processes

Key geomorphic processes

Geomorphic Processes: Flooding

Flooding drives channel change

Creates and maintains riparian habitats

Key questions:

How do different magnitude flows shape landscape?

Are key habitats being created and maintained?

Photo courtesy of Freshwaters Illustrated

Geomorphic Processes: Gravel Transport

Coarse sediment is building block of the channel and floodplain habitats

Key questions: Balance between gravel supply and transport?Future distribution and size of gravel bars?

Photos courtesy of Freshwaters Illustrated

(preliminary) Estimates of Gravel Transport

Geology and Slope

Estimate Gravel Yield

Gravel routed through stream

network

Abrasion

Final gravel flux

Many uncertainties anddoes not account for bank erosion

Gravel supply, without dams

Gravel Supply(preliminary) Estimates

of Gravel Transport

Geology and Slope

Estimate Gravel Yield

Gravel routed through stream

network

Abrasion

Final gravel flux

Many uncertainties anddoes not account for bank erosion

Trapping by dams

Gravel supply,

including dams

~60% decrease in gravel transport

Gravel Supply vs Transport

Supply:Gravel volume and characteristics

Transport Capacity:Amount of gravel a river can carry

Gravel supply vs transport

When supply equals or exceeds transport:

- Larger, more numerous gravel bars

- More channel shifting

- More complex habitats

Gravel Supply vs Transport

When supply equals or exceeds transport:

- Larger, more numerous gravel bars

- More channel shifting

- More complex habitats

Lower North Santiam

Rivers with ample bed-material sediment tend to look like the lower North Santiam,

but no comprehensive gravel transport studies have been conducted for this river

Gravel Supply vs Transport

When transport capacity exceeds supply:

- Fewer gravel bars- More stable channel planform- Coarsening of channel bed- Potential for incision- Fewer, less complex habitats

Gravel Supply vs Transport

Middle Fork Willamette River

When transport capacity exceeds supply:

- Fewer gravel bars- More stable channel planform- Coarsening of channel bed- Potential for incision- Fewer, less complex habitats

Rivers with limited gravel transport tend to look like the Middle Fork, but no

comprehensive studies of gravel transport have been conducted for this river

Geomorphic Processes: Floodplain Vegetation Succession

Riparian forests provide habitat for aquatic, riparian and terrestrial species, enhance water quality and contribute large wood

Key Questions:

Are diverse forest mosaics being created and maintained?

Extent and implications of vegetation encroachment?

Aerial photo of Upper Willamette downstream of Harrisburg; Photos courtesy of Freshwaters Illustrated

Vegetation Succession: Emerging Issues and Questions

Willamette near Snag Boat Bend

Flow direction

Recent research shows:

1) Channel stability limits bar growth

2) Areas of new colonization are often “reset” by high flows.

3) Existing stands are maturing – increase in forest within 2 yr floodplain but losses elsewhere

Implications for stand diversity?

Sources: Cline and McAllister, 2012; Hulse and others, unpublished data

Bank protection

Key QuestionsRegarding channel processes in Willamette floodplain

1) What habitats and landforms compose modern floodplain?

2) How are geomorphic processes currently shaping these habitats?

3) How do landforms and geomorphic processes relate to vegetation?

How do different flows shape habitats?

Are key habitats being created and maintained?

Where is gravel coming from?

What is the balance between gravel supply

and transport?

How does gravel transport relate to habitat availability?

Are forest mosaics being created and maintained?

What is the extent and implications of vegetation

encroachment?

Numerous questions and issues….

Three overarching questions:

Future Steps to Address Knowledge GapsComprehensive studies to understand geomorphic processes

shaping modern Willamette Floodplains

1. Create an inventory of habitats and landforms• Detailed geomorphic mapping of floodplain based on

demonstration study conducted in 2012 (see poster session)

2. Relate landforms with formative processes• Evaluate gravel supply and transport using multiple approaches• Assess channel and floodplain evolution with repeat photos and

surveys

3. Assess vegetation succession• Evaluate relationships between geomorphology, hydrology and

vegetation for broad areas of floodplain• Comprehensive monitoring and repeat photo analyses

Next Steps

Anticipated Publications:

Willamette geomorphic “issues” study: Summer 2013

Western Oregon gravel transport and channel morphology: late 2013 (?)

Acknowledgements

Pam Wiley (MMT)

Eric Jones (MMT)

Ken Bierly (OWEB)

Jenny Ayotte (BSWCD)

Jeremy Monroe (Freshwaters Illustrated)

Pete Klingeman (OSU-retired)

Brian Bangs (ODFW)

Kirk Schroeder (ODFW)

Greg Taylor (USACE)

Steve Smith (USFWS-retired)

Steve Cline (EPA)

Kathryn Boyer (OSU; NRCS-retired)

Joe Moll (McKenzie River Trust)

Chris Vogel (McKenzie River Trust)

Funding:Benton Soil and Water Conservation DistrictUSGS Cooperative Water ProgramMeyer Memorial Trust and Oregon Watershed Enhancement Board

Leslie Bach (TNC)

Dan Bell (TNC)

Jason Knuckles (TNC)

Anne Mullan (NOAA Fisheries)

Chris Budai (USACE)

Rick Bastach (City of Portland)

Scott Wright (RDG)

Troy Brandt (RDG)

Janine Castro (USFWS/NOAA)

Rob Markel (NOAA Fisheries)

Sarah Schanz (Univ. Washington)

Joseph Mangano (Colorado State Univ.)

Assistance and insight to Willamette River issues:

Questions?