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Rc201 day 1 jennings 10

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  • 1. Stream Restoration
    Greg Jennings, PhD, PE
    Professor, Biological & Agricultural Engineering
    North Carolina State University
    jennings@ncsu.edu
  • 2. What is a Stream?
    … a body of water with a current, confined within a bed and streambanks
    Synonyms:  bayou, beck, branch, brook, burn, creek, crick, kill, lick, rill, river, rivulet, run, slough, syke
    Streams are conduits in the water cycle and also important habitats
    Photo Credit: Eve Brantley, Auburn University
  • 3. Streams are Ecosystems
    • Communities of organisms and their physical, chemical, and biological environments
  • What Makes a Stream Healthy?
    • Bed stability & diversity
    • 4. Sediment transport balance
    • 5. In-stream habitat & flow diversity
    • 6. Bank stability (native plant roots)
    • 7. Riparian buffer (streamside forest)
    • 8. Active floodplain
  • Bed Stability & Diversity
    • Appropriate size sediments to resist shear stress
    • 9. Riffle/Pool sequences in alluvial streams
    • 10. Step/Pool sequences in high-gradient streams
    Photo Credit: Eve Brantley, Auburn University
  • 11. Sediment Transport Balance
    • Minor erosion & deposition
    • 12. Alluvial bars and benches
    • 13. Sufficient stream power to avoid aggradation
    • 14. No net change in sediment over long time
  • In-stream Habitat & Flow Diversity
    Overhanging Bank
    Roots
    Wood
    Pool
    Leaf Pack
    Plants
    Riffle
    Rocks
  • 15. Bank Stability
    • Dense native plant roots
    • 16. Low banks with low stress
  • Riparian Buffer (Streamside Forest)
    • Diverse native plants
    • 17. Food and shade
  • Active Floodplain
    • Regular (every year) flooding to relieve stress
    • 18. Riparian wetlands
    • 19. Stormwater retention & treatment
  • Why Restoration?
  • Stream Insults
    • Straightening & dredging
    • 27. Floodplain filling
    • 28. Watershed manipulation
    • 29. Sedimentation & stormwater
    • 30. Pollution discharges
    • 31. Utilities & culverts
    • 32. Buffer removal
    • 33. Disdain & neglect
  • Ecosystem Restoration
    • Activities that initiate or accelerate the recovery of ecosystem health, integrity, and sustainability (SER, 2004).
  • Standards for ecologically successful river restoration
    Palmer et al., Journal of Applied Ecology, 2005, 42, 208–217
    design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river
    river’s ecological condition must be measurably improved
    river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed
    during the construction phase, no lasting harm should be inflicted on the ecosystem
    pre- and post-assessment must be completed and data made publicly available
  • 34. Outcomes of Ecosystem Restoration
    • Habitats
    • 35. Water quality
    • 36. Natural flow regimes
    • 37. Recreation & aesthetics
    • 38. Public acceptance
  • Restoration Components
    Channel morphology & floodplain connection
    In-stream structures
    Streambank bioengineering
    Riparian buffers & habitat enhancements
    Stream crossings
    Stormwater/watershed management
    Monitoring & maintenance
    Public access & education
  • 39. Healthy “reference” streams serve as design templates
  • 40. Natural Stream Channel Stability
    (from Leopold)
    River has a stable dimension, pattern and profile
    Maintains channel features (riffles, pools, steps)
    Does not aggrade (fills) or degrade (erodes)
  • 41. 1. Channel Morphology & Floodplain Connection
    • Dimension (bankfull & flood flow)
    • 42. Pattern (meander)
    • 43. Profile (bed profile)
    • 44. Floodplain connection
    2005NCSU Rocky Branch2006
  • 45. 2008NCSU Rocky Branch
  • 46. Bankfull Stage: Water fills the active channel and begins to spread onto the floodplain
    Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
  • 47. Priority 1:Raise channel to existing valley and construct new meandering channel
    Rain will come during and immediately following construction!
    2006 Town Creek Tributary 2007
  • 48. 2008 Town Creek Tributary
  • 49. Priority 1:Raise channel to existing valley and construct new meandering channel
    2008Purlear Creek 2009
  • 50. 2009Purlear Creek
  • 51. Priority 1
    Priority 2
  • 52. Priority 2:Excavate lower floodplain and construct new meandering channel
    2008Trib to Saugatchee Creek 2008
  • 53. Entrenchment Ratio = Wfpa / Wbkf = 75/15 = 5
    Wfpa
    Wbkf
  • 54. Priority 2:Excavate lower floodplain and construct new meandering channel
    2007 Cary Walnut Creek Tributary 2008
    Photo Credit: David Bidelspach, Stantec, Inc.
  • 55. 2008 Cary Walnut Creek Tributary
  • 56. Priority 3:Excavate narrow floodplain benches in confined systems
    2009Little Shades Creek 2010
  • 57. Entrenchment Ratio = Wfpa / Wbkf = 60/38 = 1.6
    Wfpa
    Wbkf
  • 58. Before
    Seoul, Korea
    Cheonggye
    “Extreme Restoration”
    After
    Fac. of Environment & Life Sciences, Seoul Women's University
  • 59. Fac. of Environment & Life Sciences, Seoul Women's University
    After
    Before
  • 60. Fac. of Environment & Life Sciences, Seoul Women's University
    Restoration process of Cheonggye stream
  • 61. Fac. of Environment & Life Sciences, Seoul Women's University
    Fac. of Environment & Life Sciences, Seoul Women's University
    Typical cross-section of the restored stream section
  • 62. Fac. of Environment & Life Sciences, Seoul Women's University
  • 63. Stream Design Approaches
    Threshold Channel
    Alluvial Channel
    Regime Equations
    Analogy (Reference Reach)
    Hydraulic Geometry
    Analytical Models
    Combination of Methods
  • 64. Threshold Channels
    Rigid boundary systems
    Simple design approach: select channel configuration where the stress applied during design conditions is below the allowable stress for the channel boundary
  • 65. Threshold Channels
  • 66. Shear Stress
  • 67. Threshold Channels – Shear Stress
  • 68. Shear Stress
     = Rs
     = Shear Stress (lb/ft2)
     = Unit Weight of Water = 62.4 lb/ft3
    R = Hydraulic Radius (ft) = A/P
    s = Energy Slope (water surface) (ft/ft)
    A = Riffle Cross-Section Area (ft2)
    P = Wetted Perimeter (ft) [P ~ Wbkf + 2 x Dbkf]
    http://www.epa.gov/warsss/sedsource/bedload.htm
  • 69. Threshold Channels – Shear Stress
  • 70.
  • 71.
  • 72. Shear Stress Around Bends
  • 73. Shear Stress Distribution
    Flow around bends
    creates secondary currents
    higher shear stresses on the channel sides and bottom compared to straight reaches
    maximum shear stress in a bend is a function of the ratio of channel curvature to bottom width
  • 74. Shear Stress Distribution
    from Chang, 1988
  • 75. Shear Stress Distribution
  • 76. Alluvial Channels
    Movable boundary systems
    Complex design approach: assess sediment continuity and channel performance for a range of flows
    Dependent variables: Width, Depth, Slope, Planform
    Independent variables: Sediment inflow, Water inflow, Bank composition
    Empirical & Analytical approaches should be used concurrently
  • 77. Steady State Equilibrium
    dimension, pattern and profile of the river and its velocity have adjusted to transmit the discharge and sediment load from its catchment under the present climate and land use conditions without any systematic erosion or deposition; namely regimeconditions (Hey)
  • 78. Assumption: Stream Behavior Is Predictable
    Streams evolve to a state of dynamic equilibrium
    Equilibrium is a function of flow and sediment
    Equilibrium is naturally associated with a main channel and a flood-prone area
    The main channel is formed by the effective (“bankfull”) discharge over time
    Alluvial stream meandering
    is predictable
  • 79. Design Criteria Selection
    From Will Harman, Stream Mechanics
  • 80. Alluvial Channels – Regime Approach
    Empirical equations
    Use as a check
    Hey equations:
  • 81. Alluvial Channels – Analogy Approach
    Reference reach: Must have similar bed/bank materials, sediment inflow, slope, valley type, and hydrograph
    Upstream/downstream of design reach is best
    Nearby similar watershed acceptable
    Use as a starting point or check (BE CAREFUL)
  • 82. Alluvial Channels – Hydraulic Geometry
  • 83. Alluvial Channels – Hydraulic Geometry
  • 84.
  • 85.
  • 86. Hydraulic Geometry
    National Center for Earth Dynamics
    http://www.nced.umn.edu/Stream_Restoration_Toolbox.html
    Single-Thread Gravel-Bed Rivers Have Consistent Bankfull Geometries
  • 87. Alluvial Channels – Analytical Methods
    Choose appropriate model
    Assess a range of solutions
    Use as a check
    Analytical Design Approach, Shields, 2006
  • 88. Combination Approach to Natural Channel Design
    Existing Conditions – valley, watershed, constraints
    Design Goals
    Design Criteria
    Regime Equations
    Analogy (Reference Reach)
    Hydraulic Geometry (Regional Curves)
    Other Restoration Projects
    Analytical Models
  • 89. Natural Channel Design Approach, from Rosgen, 2006
  • 90. Design Criteria Selection
    From Will Harman, Stream Mechanics
  • 91. Reference Reach Versus Design Reach
    Stream restoration project immediately after construction; floodplain devoid of vegetation
    Reference reach with mature forest
    From Will Harman, Stream Mechanics
  • 92. Reference Reach Pattern
    From Will Harman, Stream Mechanics
  • 93. Reference Reach:
    • Upstream/downstream
    • 94. Same watershed
    • 95. Similar watershed
    • 96. Historical photos
    From Will Harman, Stream Mechanics

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