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Asce nc jennings
- 1. Stream Restoration Innovations andOpportunities Greg Jennings, PhD, PE Professor, Biological & Agricultural Engineering North Carolina State University jennings@ncsu.edu
- 2. Stream: A systemof fluvial forms & habitats • Channel (bed & banks) • Floodplain • Water • Sediment • Plants & animals Photo Credit: Eve Brantley, Auburn University
- 3. Streams are Ecosystems • Communities of organisms and their physical, chemical, and biological environments
- 4. What makes astream healthy? 1. Bed stability & diversity 2. Sediment transport balance 3. In-stream habitat & flow diversity 4. Bank stability (native plant roots) 5. Riparian buffer (streamside forest) 6. Active floodplain 7. Healthy watershed
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- 6. Stream Impairments • Straightening& dredging • Floodplain filling • Watershed manipulation • Sedimentation & stormwater • Pollution discharges • Utilities & culverts • Buffer removal • Disdain & neglect
- 7. Ecosystem Restoration § Activitiesthat initiate or accelerate the recovery of ecosystem health, integrity, and sustainability (SER, 2004).
- 8. Why Restoration? • Waterquality impairments • Habitat loss • Ecosystem degradation • Land loss • Safety concerns • Infrastructure damage • Flooding • Aesthetics
- 9. Standards for ecologicallysuccessful river restoration Palmer et al., Journal of Applied Ecology, 2005, 42, 208–217 1. design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river 2. river’s ecological condition must be measurably improved 3. river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed 4. during the construction phase, no lasting harm should be inflicted on the ecosystem 5. pre- and post-assessment must be completed and data made publicly available
- 10. Outcomes of EcosystemRestoration • Habitats & water quality • Natural flow regimes • Recreation & aesthetics • Public enthusiasm
- 11. Restoration Components 1. Channel morphology 2. Floodplain structure 3. Hydrologic & hydraulic analysis 4. In-stream structures 5. Habitats & vegetation 6. Site & watershed conditions 7. Monitoring, maintenance, education
- 12. Stream Design Approaches 1. Threshold Channel 2. Alluvial Channel a. Regime Equations b. Analogy (Reference Reach) c. Hydraulic Geometry d. Analytical Models 3. Combination of Methods
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- 14. Alluvial Channels 1. Movableboundary systems 2. Complex design approach: assess sediment continuity and channel performance for a range of flows 3. Dependent variables: Width, Depth, Slope, Planform 4. Independent variables: Sediment inflow, Water inflow, Bank composition 5. Empirical & Analytical approaches should be used concurrently
- 15. 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 regime conditions (Hey)
- 16. Alluvial Channels –Analogy Approach 1. Reference reach: Must have similar bed/bank materials, sediment inflow, slope, valley type, and hydrograph 2. Upstream/downstream of design reach is best 3. Nearby similar watershed acceptable 4. Use as a starting point or check (BE CAREFUL)
- 17. Alluvial Channels –Hydraulic Geometry
- 18. Hydraulic Geometry Regional Curves 10000 NC Piedmont NC Mtn 1000 MD Alleghany Bankfull Discharge, Q (cfs) MD NY 100 VT OH 01 OH 05 10 OK SW OR Pacific NW 1 AZ 0.1 1 10 100 AZ & NM Drainage Area (sq mi)
- 19. Hydraulic Geometry Regional Curves 1000 NC Piedmont NC Mtn MD Alleghany Cross-‐section Area (sq ft) 100 MD NY VT OH 01 10 OH 05 OK SW OR Pacific NW 1 AZ 0.1 1 10 100 AZ & NM Drainage Area (sq mi)
- 20. Combination Approach toNatural Channel Design 1. Existing Conditions – valley, watershed, constraints 2. Design Goals 3. Design Criteria a. Regime Equations b. Analogy (Reference Reach) c. Hydraulic Geometry (Regional Curves) d. Other Restoration Projects 4. Analytical Models
- 21. 1. Channel Morphology • Dimension (baseflow, bankfull, flood flows) • Pattern (meandering, straight, braided) • Profile (bedform – riffle, run, pool, glide, step) Photo Credits: Darrell Westmoreland, North State Environmental, Inc. 2005 South Fork Mitchell River 2006
- 22. 2011 South Fork Mitchell River
- 23. 2011 South Fork Mitchell River
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- 25. Natural Stream ChannelStability (from Leopold) • River has a stable dimension, pattern and profile • Maintains channel features (riffles, pools, steps) • Does not aggrade (fills) or degrade (erodes)
- 26. Dimension (cross-section) • Area • Width • Depth • Width/Depth Ratio • Entrenchment Ratio • Bank Height Ratio
- 27. Bankfull Stage: “incipientflooding” “corresponds to the discharge at which channel maintenance is the most effective, that is, the discharge at which moving sediment, forming or removing bars, forming or changing bends and meanders, and generally doing work results in the average morphologic characteristics” (Dunne & Leopold, 1978) Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
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- 29. Bankfull Width, Wbkf= 36 ft; Bankfull Area, Abkf = 112 ft2 Mean Depth, dbkf = Abkf / Wbkf = 112 / 36 = 3.1 ft Width to Depth Ratio, W/d = Wbkf / dbkf = 36 / 3.1 = 11.5
- 30. BHR = 5.3/ 2.5 = 2.1
- 31. Entrenchment Ratio =Wfpa / Wbkf = 75/15 = 5
- 32. Meandering Stream: AlluvialForms Riffle Point Bar (deposition) Glide Run Pool
- 33. Sinuosity = streamlength / valley length K = 1850 / 980 = 1.9 Valley Length
- 34. Meander Length Ratio= meander length / width = 78/15 = 5.2 Meander Width Ratio = belt width / width = 57/15 = 3.8 Radius of Curvature Ratio = radius / width = 23/15 = 1.5 Belt Width Meander Length
- 35. Profile (bedform) Water Surface Riffle Slope Run Slope Glide Slope Thalweg Pool Slope Pool Spacing, Lp-p Riffle Slope Ratio, Srif / Sav Pool Slope Ratio, Spool / Sav Pool-to-Pool Spacing Ratio, Lp-p / Wbkf
- 36. 2. Floodplain Structure • Regular (every year) flooding to relieve stress • Floodwater retention & riparian wetlands • Stormwater discharge retention & treatment
- 37. Priority 1: lift channel Incised Stream Priority 2 & 3: lower floodplain Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
- 38. Priority 1: Raisechannel to existing valley and construct new meandering channel ER = 15; W/d = 12 Rain will come during and immediately following construction! 2006 Town Creek Tributary 2007
- 39. Entrenchment Ratio =Wfpa / Wbkf = 150/10 = 1.6 2008 Town Creek Tributary
- 40. Priority 1: Raisechannel to existing valley and construct new meandering channel ER = 7; W/d = 14 2008 Purlear Creek 2009
- 41. Entrenchment Ratio =Wfpa / Wbkf = 100/14 = 7 2009 Purlear Creek
- 42. Priority 2: Excavatelower floodplain and construct new meandering channel ER = 6; W/d = 11 2008 White Slough 2010
- 43. Entrenchment Ratio =Wfpa / Wbkf = 72/12 = 6 White Slough 2010
- 44. Priority 2: Excavatelower floodplain and construct new meandering channel ER = 5; W/d = 11 2008 Trib to Saugatchee Creek 2008
- 45. Priority 2: Excavatelower floodplain and construct new meandering channel 2004 NCSU Rocky Branch 2005
- 46. 2006 NCSU Rocky Branch 2006
- 47. 2008 NCSU Rocky Branch
- 49. Entrenchment Ratio =Wfpa / Wbkf = 48/12 = 4
- 50. Priority 3: Excavatenarrow floodplain benches in confined systems ER = 2.2; W/d = 12 2005 NCSU Rocky Branch 2006
- 51. 2008 NCSU Rocky Branch
- 52. Priority 3: Excavatenarrow floodplain benches in confined systems ER = 1.6; W/d = 15 2009 Little Shades Creek 2010
- 53. Entrenchment Ratio =Wfpa / Wbkf = 60/38 = 1.6
- 54. Little Shades Creek 2010
- 55. Priority 3. Excavatefloodplain benches and add structures to maintain straight channel ER = 1.8; W/d = 14 2000 NCSU Rocky Branch 2001
- 56. NCSU Rocky Branch 2008
- 57. 3. Hydrologic &Hydraulic Analysis Qbkf: Bankfull discharge (cfs) appropriate for watershed size, sediment transport & valley conditions Vav = Qbkf / Abkf: Bankfull average velocity (ft/s) appropriate for valley, soils, bed material τav: Bankfull average applied shear stress (lb/ft2) & local max stresses appropriate for sediment transport conditions & bed/ bank restistance ωav: Bankfull average stream power (lb/ft/s) appropriate for sediment transport conditions Riffle substrate size distribution appropriate for hydraulic conditions & habitats Streambank protection to resist erosion (short-term & long-term)