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Biological Objectives Tied to Physical Processes

This presentation by Dr. William Trush and Scott McBain outlines the interconnections between geomorphology and biology in river ecosystems. Focusing on historical perspectives and data-driven analysis, they discuss how physical processes influence biological integrity in alluvial rivers. Key topics include hydrograph analysis, channel morphology, and the impacts of dams on sediment supply and spawning habitats. The need for a dual approach—incorporating both bottom-up biological and top-down geological perspectives—is emphasized as crucial for effective river management and restoration.

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Biological Objectives Tied to Physical Processes

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  1. Biological Objectives Tied to Physical Processes Dr. William Trush Scott McBain Arcata, CA

  2. Outline • Geomorphic-Hydrology work with Biologist • Geomorphic-Biotic linkages • Attributes of alluvial river integrity • Analytical techniques which include: Hydrograph component analysis, bar morphology, integration • Reconsideration of standard techniques on assessing impacts of dams

  3. Historical Perspective • Need to have a good understanding of how the system historically functioned, both physical components and biotic components • Evaporation • Precipitation • Different Species • Variety of hydrologic regimen • Variable geology

  4. Conceptual Framework • For all take note of: Human land use and flow regulation, natural disturbance

  5. Bottom-Up vs. Top-Down • Bottom-Up- Biologist • Start under water, without understanding the history and geomorphic processes. They never challenge the base line of the river. • Top-Down- Geologist • Start above water need to consider a biological stand point. • Have to approach both ways- integration is the key

  6. Processes You Need To Go Through… • Data • Spend time getting historical condition, land and species • Conceptual model • Objectives

  7. Priority Hypothesis • Geomorphic • Dam has eliminated upstream sediment supply, decreasing in-channel coarse sediment storage • Salmonid • Spawning gravel supply has been decreased • Spawning habitat is limiting salmonid production

  8. Attributes of Alluvial Rivers • Historical Model of “Trinity River” • Look at conceptual models to identify key process and formation that maintained the ecosystem • The process of developing the attributes is most important and different for every river

  9. Attributes of Alluvial Rivers cont. • Spatially complex channel morphology (migrate, meander, side channels) • Flows and water quality are predictably variable (Trends in river that are consistent per year during certain times) • Bed moves frequently (1-2 year) • Bed scour and fill (5-10 year) • Balance fine and coarse sediment • Channel migrates/avulsion

  10. Attributes of Alluvial Rivers cont. • Floodplains (oxbows, fine sediment dep.) • Channel Resettling floods (20-50 yrs. Large scale geomorphic change) • Plant communities • Fluctuating ground water table (wetlands and animals)

  11. Channel Complexity • Very Complex • Point bars (plants), scours, oxbows, sheer zones/pools (fish), side channels, variable particle size

  12. Create and Maintain Channel Morphology • Hydrograph • Print our every hydrograph for the periods of record, develop hypothesis • Conduct water year analysis to evaluate inter-annual flow variability (wet year vs. dry year) • Intra-annual flow variability with in water year, evaluate changes relate geomorphic processes and life history of key biota • Link biota to hydrology

  13. Different water years = Different ecological functions

  14. Other Biological Hotspots • Sediment deposition • Channel complexity (bars, side channels) • Riparian vegetation • Spawning areas • Amphibian egg laying locations • Large wood accumulation

  15. Suggestions • Historical perspective to understand how the system naturally worked • Hypotheses on how project changes the components of the system (Geomorphic-Biotic) • Use top/down and bottom/up approach with lots of coordination between physical scientist and biologist • No river is the same, nor does every dam have the same impacts

  16. Case Study 1 • Overview of hydrology, geomorphology, and channel morphology of the Clavey River • Develop hypotheses • Illustrate some conceptual models and analytical tools useful for access dam-related impacts to steep bedrock rivers

  17. Summary of Changes • Substantial loss of flow volume • Substantial reduction on flood magnitude and frequency • Constant year found base flows • Loss of coarse sediment supply • Reduction or loss of fine sediment • Downstream tributaries and valley walls still contribute fine and coarse sediment to channel

  18. Potential Impacts • Accumulation of fine sediment and gravels in channel • Riparian and upland vegetation intrusion • Abandoned side channels and ponded areas • Reduction of residual pool volume by gravel-boulder filling • And…

  19. Potential Impacts • Reduced magnitude, duration, and frequency of bed mobility of alluvial features • Reduced coarse sediment storage immediately downstream of the dam

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