Processes and Landforms of the Willamette River and Floodplain

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Presented by Rose Wallick of USGS as part of the Science Progress Report at Within Our Reach 2012.

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Processes and Landforms of the Willamette River and Floodplain

  1. 1. Processes and Landforms of the Willamette River and Floodplain: Current Understanding and Information Needs Rose Wallick Dave Hulse Jim O’Connor Stan Gregory Krista Jones Mackenzie Keith Charles CannonU.S. Department of the InteriorU.S. Geological Survey
  2. 2. Introduction• Previous studies Upper Willamette documented historical changes and created Historical Channel Change rich datasets• Much is still unknown about “modern” channel processes 1850 1995 Map sources: Willamette Planning Atlas; Hulse and others 2001
  3. 3. Emerging Management Challengesfor the Willamette FloodplainWhat 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
  4. 4. Geomorphic Processes ShapingWillamette Valley Floodplains
  5. 5. Purpose and ApproachOverarching goal:Build a roadmap towards better understanding ofgeomorphic processes in Willamette ValleyStudy Approach: Describe floodplain landforms and processes Explain our current understanding Identify major knowledge gaps Outline future studies
  6. 6. Study AreaWillamette Geomorphic Floodplain Alluvial, gravel-bed portion of Willamette River and major tributaries Landforms and geomorphic processes broadly similar Interconnected system of landscapes and ecosystems
  7. 7. Comparison of Landforms along Willamette RiverHigh Channel Complexity Low Channel Complexity Stable, vegetated bar SideGravel channel barsSidechannels Upper Willamette Middle Willamette upstream of Harrisburg near Albany Aerial photographs from 2011
  8. 8. Comparison of Landforms along TributariesHigh Channel Complexity Low Channel Complexity Side channels Stable, vegetated bars Active Side bars channels Lower North Santiam Middle Fork near Wiseman Island near Jasper State Park Aerial photographs from 2011
  9. 9. Diversity of Channel Morphologies Reflects Differences in Geomorphic Processes Keygeomorphic processes
  10. 10. Geomorphic Processes: FloodingFlooding drives channel changeCreates and maintains riparian habitatsKey questions:How do different magnitude flows shape landscape?Are key habitats being created and maintained? Photo courtesy of Freshwaters Illustrated
  11. 11. Geomorphic Processes:Gravel Transport Coarse sediment is building block of the channel and floodplain habitatsKey questions:Balance between gravel supply and transport?Future distribution and size of gravel bars? Photos courtesy of Freshwaters Illustrated
  12. 12. Gravel(preliminary) Estimates supply, withoutof Gravel Transport dams Geology Estimate and Slope Gravel Yield Abrasion Gravel routed through stream network Final gravel flux Many uncertainties and does not account for bank erosion
  13. 13. Gravel Gravel(preliminary) Estimates supply, Supply includingof Gravel Transport dams Geology Estimate and Slope Gravel Yield ~60% decrease in gravel transport Abrasion Gravel routed through stream network Trapping by dams Final gravel flux Many uncertainties and does not account for bank erosion
  14. 14. Gravel Supply vs Transport Supply: Transport Capacity:Gravel volume and characteristics Amount of gravel a river can carry
  15. 15. Gravel supply vs transport When supply equals or exceeds transport:- Larger, more numerous gravel bars- More channel shifting- More complex habitats
  16. 16. Gravel Supply vs Transport When supply equals or exceeds transport:- Larger, more numerous gravel bars- More channel shifting- More complex habitatsRivers with ample bed-material sedimenttend to look like the lower North Santiam, but no comprehensive gravel transportstudies have been conducted for this river Lower North Santiam
  17. 17. 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
  18. 18. 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 habitatsRivers with limited gravel transport tend to look like the Middle Fork, but nocomprehensive studies of gravel transport have been conducted for this river Middle Fork Willamette River
  19. 19. Geomorphic Processes:Floodplain Vegetation SuccessionRiparian forests provide habitat for aquatic, riparian and terrestrialspecies, enhance water quality and contribute large woodKey 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
  20. 20. Vegetation Succession: Emerging Issues and QuestionsRecent research shows: Bank protection1) Channel stability limits bar growth2) 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 Flow direction Implications for stand diversity? Willamette near Snag Boat Bend Sources: Cline and McAllister, 2012; Hulse and others, unpublished data
  21. 21. Key QuestionsRegarding channel processes in Willamette floodplain Numerous questions and issues….How do different flows Are key habitats being What is the balance Where is gravel shape habitats? created and maintained? between gravel supply coming from? and transport?Are forest mosaics being What is the extent and implications of vegetation How does gravel transportcreated and maintained? relate to habitat availability? encroachment? Three overarching questions: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?
  22. 22. Future Steps to Address Knowledge Gaps Comprehensive studies to understand geomorphic processes shaping modern Willamette Floodplains1. 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 surveys3. Assess vegetation succession • Evaluate relationships between geomorphology, hydrology and vegetation for broad areas of floodplain • Comprehensive monitoring and repeat photo analyses
  23. 23. Next StepsAnticipated Publications:Willamette geomorphic “issues”study: Summer 2013Western Oregon gravel transportand channel morphology:late 2013 (?)
  24. 24. Acknowledgements Funding: Benton Soil and Water Conservation District USGS Cooperative Water Program Meyer Memorial Trust and Oregon Watershed Enhancement Board Assistance and insight to Willamette River issues: Pam Wiley (MMT) Leslie Bach (TNC) Eric Jones (MMT) Dan Bell (TNC) Ken Bierly (OWEB) Jason Knuckles (TNC) Jenny Ayotte (BSWCD) Jeremy Monroe (Freshwaters Illustrated) Anne Mullan (NOAA Fisheries) Pete Klingeman (OSU-retired) Chris Budai (USACE) Brian Bangs (ODFW) Rick Bastach (City of Portland) Kirk Schroeder (ODFW) Scott Wright (RDG) Greg Taylor (USACE) Troy Brandt (RDG) Steve Smith (USFWS-retired) Janine Castro (USFWS/NOAA) Steve Cline (EPA) Kathryn Boyer (OSU; NRCS-retired) Rob Markel (NOAA Fisheries) Joe Moll (McKenzie River Trust) Sarah Schanz (Univ. Washington) Chris Vogel (McKenzie River Trust) Joseph Mangano (Colorado State Univ.)
  25. 25. Questions?

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