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Biological Objectives Tied to Physical Processes

Dr. William Trush and Scott McBain discuss the relationship between geomorphic-hydrology and biology, including the impact of dams on alluvial river integrity. The presentation covers historical perspective, conceptual frameworks, analytical techniques, and case studies highlighting potential impacts.

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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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