1. Greg Jennings, PhD, PE Professor, Biological & Agricultural Engineering North Carolina State University jennings@ncsu.edu BAE 579: Stream Restoration Lesson 3: Stream Stability Assessment

2. Stream Stability 1.What is Stability? 2.Causes of Instability 3.Stability Assessment

3. What is a “Stable” Stream? “Graded” Stream: Condition of “balance between erosion and deposition attained by mature rivers” (Davis, 1902) “Dynamic Equilibrium”: Stream form & character unchanged while continuous inflow of water/sediment (Strahler, 1957) “Equilibrium Controlling Factors”: Width, depth, velocity, slope, discharge, sediment size, sediment concentration, channel roughness (Leopold, 1964) “Regime Channels”: Some erosion and deposition but no net change in dimension, pattern, and profile (Hey, 1997) “Stream Channel Stability”: ability of a stream, over time, in the present climate, to transport the sediment and flows produced by its watershed in such a manner that the stream maintains its dimension, pattern, and profile without either aggrading or degrading (Rosgen, 1996)

4. Lane’s Stream Balance Relationship

5. Causes of Instability Increase runoff Increase slope Changes in sediment load Loss of riparian buffer Floodplain filling Instream modification

6. Increase Runoff: Land Use Changes

7. Development Impacts on the Water Cycle 50% 10% 15% 55% Courtesy NEMO, Univ. of CT

8. Impervious Surfaces Across the Landscape Roads Parking Buildings Sidewalks Driveways Center for Watershed Protection

9. The Science of Stormwater… More Runoff Arriving Faster NEMO

10. Hydrologic Responses to Urbanization 1.Increased discharge 2.Increased peak discharge 3.Increased velocities 4.Shorter time to peak flow 5.More frequent bankfull events 6.Increased flooding 7.Lower baseflow 8.Less ground water recharge

14. Increase Slope Channelization Lower Reservoir Water Surface Dam Break Geologic Uplift

15. Changes in Sediment Load Development Agriculture Bank Erosion Impoundments

17. Aggradation

22. Mid-channel bar and transverse bar directing flow into a high bank causing erosion and slumping

23. Debris Occurrence Large Woody Debris Depends on Riparian Stability Beaver Dams

24. Impoundments Upstream: Decrease velocities Deposition of fine material Loss of habitat Downstream: “Hungry water” Change in flow

25. Riparian Condition (Buffer) Composition Density Potential

26. Values of Vegetation Habitats Water Quality Bank Stability Shade & Food Stream Corridor Restoration: Principles, Processes, and Practices, 10/98, by the Federal Interagency Stream Restoration Working Group (FISRWG)."

27. Streamside Forests (also known as riparian buffers) Trees, shrubs, herbs, and grasses are critical to the health of streams Buffers are the first line of defense against the impacts of polluted runoff natural vegetation buffers are especially critical in urban areas

31. Altered States Due to Disturbance Channelization Straightening Levees Hardening Mining

32. Floodplain Filling

34. Simon Channel Evolution Model Source: Simon, 1989, USACE 1990

37. Head Cut

45. VI IV V III I Original Nickpoint III IV I I I I I I I II I I I

46. G4c Alabama

47. Stream Channel Succession (WARSSS)

48. http://www.epa.gov/WARSSS/ sedsource/successn.htm

49. Stability Assessment http://www.epa.gov/warsss/index.htm

50. Entrenchment Ratio

51. Lateral Stability Meander Width Ratio Bank Erosion (BEHI)

52. Meander Width Ratio W bkf W blt MWR = W blt / W bkf W bkf = Bankfull Width of Riffle Cross-Section W blt = Belt Width

53. Bank Erosion Monitoring

54. Bank Erosion Hazard Index (BEHI)

57. 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.

59. Bank Height Ratio Very Low

60. Bank Height Ratio Moderate

61. Bank Height Ratio Very High

63. Root Depth Ratio Very Low BEHI

64. Root Depth Ratio Moderate BEHI

65. Root Depth Ratio Very High BEHI

67. Root Density Very Low BEHI

68. Root Density Moderate

69. Root Density Very High BEHI

70. Bank Angle (from horizontal)

71. Bank Angle Very Low

72. Bank Angle Moderate - High

73. Bank Angle Very High

75. Surface Protection Very Low BEHI

76. Surface Protection Moderate

77. Surface Protection Very High BEHI

78. Bank Materials Extreme Risk High Risk Very Low Risk

82. Near Bank Stress Low

83. Near Bank Stress Moderate

84. Near Bank Stress High

85. Near Bank Stress Very High