• Share
  • Email
  • Embed
  • Like
  • Save
  • Private Content
Rc201 day 1 jennings 10
 

Rc201 day 1 jennings 10

on

  • 930 views

 

Statistics

Views

Total Views
930
Views on SlideShare
929
Embed Views
1

Actions

Likes
0
Downloads
8
Comments
0

1 Embed 1

http://www.slideshare.net 1

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Rc201 day 1 jennings 10 Rc201 day 1 jennings 10 Presentation Transcript

    • Stream Restoration
      Greg Jennings, PhD, PE
      Professor, Biological & Agricultural Engineering
      North Carolina State University
      jennings@ncsu.edu
    • 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
    • Streams are Ecosystems
      • Communities of organisms and their physical, chemical, and biological environments
    • What Makes a Stream Healthy?
      • Bed stability & diversity
      • Sediment transport balance
      • In-stream habitat & flow diversity
      • Bank stability (native plant roots)
      • Riparian buffer (streamside forest)
      • Active floodplain
    • Bed Stability & Diversity
      • Appropriate size sediments to resist shear stress
      • Riffle/Pool sequences in alluvial streams
      • Step/Pool sequences in high-gradient streams
      Photo Credit: Eve Brantley, Auburn University
    • Sediment Transport Balance
      • Minor erosion & deposition
      • Alluvial bars and benches
      • Sufficient stream power to avoid aggradation
      • No net change in sediment over long time
    • In-stream Habitat & Flow Diversity
      Overhanging Bank
      Roots
      Wood
      Pool
      Leaf Pack
      Plants
      Riffle
      Rocks
    • Bank Stability
      • Dense native plant roots
      • Low banks with low stress
    • Riparian Buffer (Streamside Forest)
      • Diverse native plants
      • Food and shade
    • Active Floodplain
      • Regular (every year) flooding to relieve stress
      • Riparian wetlands
      • Stormwater retention & treatment
    • Why Restoration?
      • Water quality impairments
      • Habitat loss
      • Ecosystem degradation
      • Land loss
      • Safety concerns
      • Infrastructure damage
      • Flooding
      • Aesthetics
    • Stream Insults
      • Straightening & dredging
      • Floodplain filling
      • Watershed manipulation
      • Sedimentation & stormwater
      • Pollution discharges
      • Utilities & culverts
      • Buffer removal
      • 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
    • Outcomes of Ecosystem Restoration
      • Habitats
      • Water quality
      • Natural flow regimes
      • Recreation & aesthetics
      • 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
    • Healthy “reference” streams serve as design templates
    • 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)
    • 1. Channel Morphology & Floodplain Connection
      • Dimension (bankfull & flood flow)
      • Pattern (meander)
      • Profile (bed profile)
      • Floodplain connection
      2005NCSU Rocky Branch2006
    • 2008NCSU Rocky Branch
    • 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.
    • 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
    • 2008 Town Creek Tributary
    • Priority 1:Raise channel to existing valley and construct new meandering channel
      2008Purlear Creek 2009
    • 2009Purlear Creek
    • Priority 1
      Priority 2
    • Priority 2:Excavate lower floodplain and construct new meandering channel
      2008Trib to Saugatchee Creek 2008
    • Entrenchment Ratio = Wfpa / Wbkf = 75/15 = 5
      Wfpa
      Wbkf
    • Priority 2:Excavate lower floodplain and construct new meandering channel
      2007 Cary Walnut Creek Tributary 2008
      Photo Credit: David Bidelspach, Stantec, Inc.
    • 2008 Cary Walnut Creek Tributary
    • Priority 3:Excavate narrow floodplain benches in confined systems
      2009Little Shades Creek 2010
    • Entrenchment Ratio = Wfpa / Wbkf = 60/38 = 1.6
      Wfpa
      Wbkf
    • Before
      Seoul, Korea
      Cheonggye
      “Extreme Restoration”
      After
      Fac. of Environment & Life Sciences, Seoul Women's University
    • Fac. of Environment & Life Sciences, Seoul Women's University
      After
      Before
    • Fac. of Environment & Life Sciences, Seoul Women's University
      Restoration process of Cheonggye stream
    • 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
    • Fac. of Environment & Life Sciences, Seoul Women's University
    • Stream Design Approaches
      Threshold Channel
      Alluvial Channel
      Regime Equations
      Analogy (Reference Reach)
      Hydraulic Geometry
      Analytical Models
      Combination of Methods
    • 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
    • Threshold Channels
    • Shear Stress
    • Threshold Channels – Shear Stress
    • 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
    • Threshold Channels – Shear Stress
    • Shear Stress Around Bends
    • 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
    • Shear Stress Distribution
      from Chang, 1988
    • Shear Stress Distribution
    • 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
    • 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)
    • 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
    • Design Criteria Selection
      From Will Harman, Stream Mechanics
    • Alluvial Channels – Regime Approach
      Empirical equations
      Use as a check
      Hey equations:
    • 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)
    • Alluvial Channels – Hydraulic Geometry
    • Alluvial Channels – Hydraulic Geometry
    • 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
    • Alluvial Channels – Analytical Methods
      Choose appropriate model
      Assess a range of solutions
      Use as a check
      Analytical Design Approach, Shields, 2006
    • 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
    • Natural Channel Design Approach, from Rosgen, 2006
    • Design Criteria Selection
      From Will Harman, Stream Mechanics
    • 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
    • Reference Reach Pattern
      From Will Harman, Stream Mechanics
    • Reference Reach:
      • Upstream/downstream
      • Same watershed
      • Similar watershed
      • Historical photos
      From Will Harman, Stream Mechanics