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Floodplain Management SESSION 6

Floodplain Management SESSION 6. Stream Systems on Dynamic Earth Stream Mechanics Prepared By Donald R. Reichmuth, PhD. Stream Mechanics Framework. Objectives: 1 How floodplains first evolved after glacial retreat. 2 Basic concepts of sediment transport.

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Floodplain Management SESSION 6

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  1. Floodplain ManagementSESSION 6 Stream Systems on Dynamic Earth Stream Mechanics Prepared By Donald R. Reichmuth, PhD.

  2. Stream Mechanics Framework Objectives: 1 How floodplains first evolved after glacial retreat. 2 Basic concepts of sediment transport. 3 Stream patterns develop in bedrock areas and in alluvial valleys. 4 Streams are shaped by peak flows, stream gradient and sediment supply. 5 Gravity systems transport water and sediment. 6 Secondary currents and stream features that are formed by their action. 7 In-channel obstructions cause random energy dissipation. 8 Stream mechanics within the context case study floodplains

  3. Post Glacial RetreatStarting 15,000 Ago • River Systems Reorganize • Glacial Sediment Sources Diminish • Sea Level Raises 400 Ft. • Climate Warms & Becomes Dryer • Isostatic Rebound Begins • Homo Sapiens Colonize The Americas • Megafauna Become Extinct

  4. OhioRiverIce Marginal FormationUtilizesPreglacialStream Sections

  5. Long Term Regional TrendsPost-Glacial Above 400 Ft. Elev. Sediment Deficient Downcutting Prevails 20 To 400 Ft. Elev. Influenced By Sea Level Change Valley Filling Dominant Below 20 Ft. Elev. Tectonic Behavior Controls Channels Impacted By Sinking Or Uplift

  6. Channel Evolution

  7. Blocked Valleys Example

  8. Post Glacial ConditionsNorth Central United States

  9. Paleo-Floodplain DevelopmentImpacts of Extinct Keystone Species

  10. Paleo-Indian HuntersAttacking A Huge Bison latifronsWith The Help of Domesticated Dogs

  11. Giant Beaver (Castoroides ohioensis)Became Extinct 10,000 Years AgoEstimated Weight -- 218 kg.Estimated Length -- 2.5 metersSize Relative To Modern Beavers Shown

  12. Giant Beaver Fossil Sites(Sites Marked By Red Dots)

  13. Pre-Columbus Floodplain DevelopmentFloodplain Stabilization Efforts Of Beaver

  14. Historic Beaver RangePrior To Widespread Trapping

  15. Post GlacialModelBeaverStabilizedDrainage

  16. Beaver Stabilized Drainage

  17. BeaverLostActiveVertical&HorizontalErosionBegins

  18. Lost Base Flow Storage

  19. Effects Of Beaver IntroductionTierra del Fuego, Argentina

  20. Basic Concepts

  21. LowerMississippiRiverSystem AggradingLevees Widespread Local Dams Stop Sediment MovementChannel Change Likely

  22. Mississippi Valley Cross-Section

  23. Mississippi Valley Cross-Section

  24. Mississippi Valley Cross-Section

  25. MississippiRiverDelta EvolutionFuture ShiftTo TheAtchafalayaRiver Basin Likely

  26. Note:Flip-FloppingCyclic20-40 Yr.CycleTypical

  27. CommonCausesFor Deposition

  28. Other Depositional Patterns

  29. Typical Fan Utilization

  30. Alluvial Fan Case Study

  31. Alluvial FanFloodplainModel

  32. Fan Apex Area Details

  33. Typical Flood Channel

  34. Unique Alluvial Fan Flood Hazards

  35. Model Comparison

  36. Other Depositional Patterns

  37. Other Depositional Patterns

  38. Stream Flow Analysis 1st Level – Flow Downhill Gravity Controls 2nd Level – Secondary Currents Bed Friction Controls 3rd Level – Random Eddies Obstructions Control

  39. Gravity SystemsPotential Energy(Height)Converts ToKinetic Energy(Velocity)OrFriction Loss

  40. Designer’s Toolkit

  41. Flow Velocity Relationships

  42. Channel FeaturesDetermined By Secondary Currents Vertically Stable (Meandering) Streams: Meander Shape Thread (Thalweg) Location Erosion/Deposition Pattern Bar Shape Mid-Channel Undertow Depositional (Braided) Streams: Mid-Channel Island Formation

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