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Floodplain Management SESSION 7

Floodplain Management SESSION 7. Stream Systems on Dynamic Earth Floodplain Management Principles & Practice Prepared By Donald R. Reichmuth, PhD. Management Framework. Objectives: 1 Stream sediment cycle in terms of source, transport and deposition.

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Floodplain Management SESSION 7

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  1. Floodplain ManagementSESSION 7 Stream Systems on Dynamic Earth Floodplain Management Principles& Practice Prepared By Donald R. Reichmuth, PhD.

  2. Management Framework Objectives: 1 Stream sediment cycle in terms of source, transport and deposition. 2 Difference between the engineering and geologic approaches in developing analytical tools for stream management. 3 Channel blockages and overall stream stability. 4 Behavior and stabilization methods used in drainages showing vertical instability. 5 Problems associated with horizontal stream channel migration. 6 Management practices to determine how to insure low impact development. 7 Present floodplain as a product of the geological floodplain -- case study exercises 8 Module 2 examination.

  3. Elements Of Channel Formation

  4. Analytical Methods Engineering Approach Initiated By Irrigation Designers Mathematical Approximations Equations Have Limited Utility Geologic Approach Initiated By Field Explorers Descriptive Physical Principals Universal Concepts Developed

  5. Energy EquationsNote:Extra Friction Loss For Expanding Sections

  6. Stream Problem Types Channel Blockage In-channel Obstructions Geologic Accidents Impoundments Vertical Change Headcutting Channel Aggradation Horizontal Change Meander Loop Migration Bank Erosion Channel Cutoffs

  7. Channel Blockages Blockages can vary in size from a single downed tree to total channel filling.

  8. Effects Of In-stream Obstructions

  9. Debris Flow ExampleAmero, Colombia -- 1985

  10. Regional Uplift Erosion PatternsNote: Colorado River Maintained Original Grade

  11. Cross Section ViewNote: Grand Canyon Formed At TopOf Structural Warping

  12. FromCanyons of the ColoradoByJ. W. Powell1895

  13. ErosionPatternsNote:Stream GradientMaintainedDuring Tectonic Uplift

  14. Effects Of Dams

  15. Colorado River HydrographBelow Lake Powell

  16. Clean Water ReleasesFrom Lake Powell -- Nov. 2004

  17. Typical Fish Passage ProblemNote:The Extreme Turbulence At The Base Of The Structure

  18. Typical Concrete/ Steel Design Yakima River -- Town Diversion U.S. Bureau of Reclamation Design Age ---------------------- About 15 Yrs. Drop Height ---------- About 6 Feet Fish Ladder ---------- 4 Cells (5 Drops) Repair Costs --------- $200,000 Est. ($130,000 Spent) Other Problems ----- Apron Undercut

  19. Irrigation Diversion DamTypical Concrete Structure With Fish Ladder

  20. Improved Safety

  21. Fish Passage Proof

  22. Vertical Change The sediment availability causes most channel filling and degradation. Many regions are experiencing downcutting as earlier glacial deposits are mobilized.

  23. Headcuts – Cause & should we do anything?

  24. Headcut-Caused FailureOpen Arch Culvert --- Bed Scoured To Bedrock

  25. Vertical Grade StabilizationExcess Energy Removed With Drops

  26. Rock Drop Characteristics Stable Fish Friendly Overhead Cover Low Velocity Eddy Macro-Invertebrates Safe For Boaters --------------------------------------------- Unstable Poor Habitat Standing Wave Unsafe

  27. Rock Drop ExampleLow Flow Concentrated At Mid-Channel

  28. Horizontal Change Horizontal channel migration is most common in regions that have low stream gradients and have reached an equilibrium grade.

  29. Meander Loop CutoffLoss Of Energy DissipationMust Be ReplacedFor Stable Conditions To Exist

  30. Bank ErosionCaused By Uncontrolled Upstream Sediment Source

  31. Cumulative Impacts Low Impact Development can only occur when long range goals are adopted that minimize cumulative impacts.

  32. Quick FlushPoor Management TechniqueShifts Problems To OthersEncourages Unsound Development

  33. Floodplain UtilizationGood Management TechniqueHelps Protect Downstream ReachesIncreases Base FlowEncourages Sustainable Development

  34. Cumulative ImpactsOn Roaring Fork River Floodplain

  35. Roaring Fork River1985 Aerial View Before Highway Construction

  36. Roaring Fork RiverAerial View Of Bottleneck Area

  37. Roaring ForkRiverGround PhotoShowingFailing Gabion BasketWall

  38. Slide PresentationPrepared ByGeomax, P.C.Dr. Donald R. Reichmuth, President1023 W. 30th Ave.Spokane, WA 99203-1324Phone & FAX – 509-838-6390E-mail – geomax@comcast.net

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