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

4. Sediment transport balance

5. In-stream habitat & flow diversity

6. Bank stability (native plant roots)

7. Riparian buffer (streamside forest)

9. Riffle/Pool sequences in alluvial streams

10. Step/Pool sequences in high-gradient streamsPhoto Credit: Eve Brantley, Auburn University

12. Alluvial bars and benches

13. Sufficient stream power to avoid aggradation

18. Riparian wetlands

20. Habitat loss

21. Ecosystem degradation

22. Land loss

23. Safety concerns

24. Infrastructure damage

25. Flooding

27. Floodplain filling

28. Watershed manipulation

29. Sedimentation & stormwater

30. Pollution discharges

31. Utilities & culverts

32. Buffer removal

35. Water quality

36. Natural flow regimes

37. Recreation & aesthetics

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)

42. Pattern (meander)

43. Profile (bed profile)

44. Floodplain connection2005NCSU 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

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

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

94. Same watershed

95. Similar watershed

96. Historical photosFrom Will Harman, Stream Mechanics