Asce nc jennings

431 views
350 views

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
431
On SlideShare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
24
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Asce nc jennings

  1. 1. Stream RestorationInnovations and OpportunitiesGreg Jennings, PhD, PEProfessor, Biological & Agricultural EngineeringNorth Carolina State Universityjennings@ncsu.edu
  2. 2. Stream: A system offluvial forms & habitats•  Channel (bed & banks)•  Floodplain•  Water•  Sediment•  Plants & animals Photo Credit: Eve Brantley, Auburn University
  3. 3. Streams are Ecosystems•  Communities of organisms and their physical, chemical, and biological environments
  4. 4. What makes a stream healthy?1.  Bed stability & diversity2.  Sediment transport balance3.  In-stream habitat & flow diversity4.  Bank stability (native plant roots)5.  Riparian buffer (streamside forest)6.  Active floodplain7.  Healthy watershed
  5. 5. Healthy Streams?
  6. 6. Stream Impairments•  Straightening & dredging•  Floodplain filling•  Watershed manipulation•  Sedimentation & stormwater•  Pollution discharges•  Utilities & culverts•  Buffer removal•  Disdain & neglect
  7. 7. Ecosystem Restoration§  Activities that initiate or accelerate the recovery of ecosystem health, integrity, and sustainability (SER, 2004).
  8. 8. Why Restoration?•  Water quality impairments•  Habitat loss•  Ecosystem degradation•  Land loss•  Safety concerns•  Infrastructure damage•  Flooding•  Aesthetics
  9. 9. Standards for ecologically successful river restorationPalmer et al., Journal of Applied Ecology, 2005, 42, 208–2171.  design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river2.  river’s ecological condition must be measurably improved3.  river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed4.  during the construction phase, no lasting harm should be inflicted on the ecosystem5.  pre- and post-assessment must be completed and data made publicly available
  10. 10. Outcomes of Ecosystem Restoration•  Habitats & water quality•  Natural flow regimes•  Recreation & aesthetics•  Public enthusiasm
  11. 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. 12. Stream Design Approaches1.  Threshold Channel2.  Alluvial Channel a.  Regime Equations b.  Analogy (Reference Reach) c.  Hydraulic Geometry d.  Analytical Models3.  Combination of Methods
  13. 13. ThresholdChannels
  14. 14. Alluvial Channels1.  Movable boundary systems2.  Complex design approach: assess sediment continuity and channel performance for a range of flows3.  Dependent variables: Width, Depth, Slope, Planform4.  Independent variables: Sediment inflow, Water inflow, Bank composition5.  Empirical & Analytical approaches should be used concurrently
  15. 15. Steady State Equilibriumdimension, pattern and profile of the river and itsvelocity have adjusted to transmit the dischargeand sediment load from its catchment under thepresent climate and land use conditions withoutany systematic erosion or deposition; namelyregime conditions (Hey)
  16. 16. Alluvial Channels – Analogy Approach1.  Reference reach: Must have similar bed/bank materials, sediment inflow, slope, valley type, and hydrograph2.  Upstream/downstream of design reach is best3.  Nearby similar watershed acceptable4.  Use as a starting point or check (BE CAREFUL)
  17. 17. Alluvial Channels – Hydraulic Geometry
  18. 18. Hydraulic  Geometry  Regional  Curves 10000 NC  Piedmont NC  Mtn 1000 MD  AlleghanyBankfull   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. 19. Hydraulic  Geometry  Regional  Curves 1000 NC  Piedmont NC  Mtn MD  AlleghanyCross-­‐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. 20. Combination Approach to Natural Channel Design1.  Existing Conditions – valley, watershed, constraints2.  Design Goals3.  Design Criteria a.  Regime Equations b.  Analogy (Reference Reach) c.  Hydraulic Geometry (Regional Curves) d.  Other Restoration Projects4.  Analytical Models
  21. 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. 22. 2011 South Fork Mitchell River
  23. 23. 2011 South Fork Mitchell River
  24. 24. High-quality“reference”streams serve asdesign templates
  25. 25. 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)
  26. 26. Dimension(cross-section)•  Area•  Width•  Depth•  Width/Depth Ratio•  Entrenchment Ratio•  Bank Height Ratio
  27. 27. Bankfull Stage: “incipient flooding” “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.
  28. 28. TerraceBankfull
  29. 29. Bankfull Width, Wbkf = 36 ft; Bankfull Area, Abkf = 112 ft2Mean Depth, dbkf = Abkf / Wbkf = 112 / 36 = 3.1 ftWidth to Depth Ratio, W/d = Wbkf / dbkf = 36 / 3.1 = 11.5
  30. 30. BHR = 5.3 / 2.5 = 2.1
  31. 31. Entrenchment Ratio = Wfpa / Wbkf = 75/15 = 5
  32. 32. Meandering Stream: Alluvial FormsRiffle Point Bar (deposition)Glide Run Pool
  33. 33. Sinuosity = stream length / valley length K = 1850 / 980 = 1.9 Valley Length
  34. 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 WidthMeanderLength
  35. 35. Profile (bedform)Water Surface Riffle Slope Run Slope Glide SlopeThalweg 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. 36. 2. Floodplain Structure•  Regular (every year) flooding to relieve stress•  Floodwater retention & riparian wetlands•  Stormwater discharge retention & treatment
  37. 37. Priority 1: lift channel Incised Stream Priority 2 & 3:lower floodplainStream Corridor Restoration: Principles, Processes, and Practices.1998. Federal Interagency Stream Restoration Working Group.
  38. 38. Priority 1: Raise channel to existing valley and construct new meandering channel ER = 15; W/d = 12Rain will come during andimmediately following construction!2006 Town Creek Tributary 2007
  39. 39. Entrenchment Ratio = Wfpa / Wbkf = 150/10 = 1.62008 Town Creek Tributary
  40. 40. Priority 1: Raise channel to existing valley and construct new meandering channel ER = 7; W/d = 142008 Purlear Creek 2009
  41. 41. Entrenchment Ratio = Wfpa / Wbkf = 100/14 = 72009 Purlear Creek
  42. 42. Priority 2: Excavate lower floodplain and construct new meandering channel ER = 6; W/d = 112008 White Slough 2010
  43. 43. Entrenchment Ratio = Wfpa / Wbkf = 72/12 = 6 White Slough 2010
  44. 44. Priority 2: Excavate lower floodplain and construct new meandering channel ER = 5; W/d = 112008 Trib to Saugatchee Creek 2008
  45. 45. Priority 2: Excavate lower floodplain and construct new meandering channel2004 NCSU Rocky Branch 2005
  46. 46. 2006NCSU Rocky Branch 2006
  47. 47. 2008 NCSU Rocky Branch
  48. 48. Entrenchment Ratio = Wfpa / Wbkf = 48/12 = 4
  49. 49. Priority 3: Excavate narrow floodplain benches in confined systems ER = 2.2; W/d = 122005 NCSU Rocky Branch 2006
  50. 50. 2008 NCSU Rocky Branch
  51. 51. Priority 3: Excavate narrow floodplain benches in confined systems ER = 1.6; W/d = 152009 Little Shades Creek 2010
  52. 52. Entrenchment Ratio = Wfpa / Wbkf = 60/38 = 1.6
  53. 53. Little Shades Creek 2010
  54. 54. Priority 3. Excavate floodplain benches and add structures to maintain straight channel ER = 1.8; W/d = 142000 NCSU Rocky Branch 2001
  55. 55. NCSURocky Branch 2008
  56. 56. 3. Hydrologic & Hydraulic AnalysisQbkf: Bankfull discharge (cfs) appropriate for watershed size,sediment transport & valley conditionsVav = Qbkf / Abkf: Bankfull average velocity (ft/s) appropriate forvalley, soils, bed materialτav: Bankfull average applied shear stress (lb/ft2) & local maxstresses appropriate for sediment transport conditions & bed/bank restistanceωav: Bankfull average stream power (lb/ft/s) appropriate forsediment transport conditionsRiffle substrate size distribution appropriate for hydraulicconditions & habitatsStreambank protection to resist erosion (short-term & long-term)

×