A healthy stream has stable banks and sediment transport, with diverse in-stream habitat and flows. Key factors include stable streambeds and natural floodplains, as well as vegetated riparian buffers. Unstable streams can aggrade or degrade from changes in watershed runoff, sediment loads, slopes, and floodplain or riparian disturbances. Assessing stability uses metrics like entrenchment ratios, meander widths, and bank erosion hazard indices.

1. What Makes a Stream Healthy?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 floodplainBed Stability & DiversityAppropriate size sediments to resist shear stress

7. Riffle/Pool sequences in alluvial streams

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

9. Sediment Transport BalanceMinor erosion & deposition

10. Alluvial bars and benches

11. Sufficient stream power to avoid aggradationIn-stream Habitat & Flow DiversityOverhanging BankRootsWoodPoolLeaf PackPlantsRiffleRocks

12. Bank StabilityDense native plant roots

13. Low banks with low stressRiparian Buffer (Streamside Forest)Diverse native plants

14. Food and shadeActive FloodplainRegular (every year) flooding to relieve stress

15. Riparian wetlands

16. Stormwater retention & treatmentWhat 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)

17. Lane’s Stream Balance Relationship

18. Causes of InstabilityIncrease runoff

19. Increase slope

20. Changes in sediment load

21. Loss of riparian buffer

22. Floodplain filling

23. Instream modificationIncrease Runoff: Land Use Changes

24. 10%50%Development Impacts on the Water Cycle55%15%Courtesy NEMO, Univ. of CT

25. Impervious Surfaces Across the LandscapeCenter for Watershed ProtectionSidewalksRoadsParkingDrivewaysBuildings

26. More RunoffArriving FasterNEMOThe Science of Stormwater…

27. Hydrologic Responses to UrbanizationIncreased dischargeIncreased peak dischargeIncreased velocitiesShorter time to peak flowMore frequent bankfull eventsIncreased floodingLower baseflowLess ground water recharge

32. Increase SlopeChannelization

33. Lower Reservoir Water Surface

34. Dam Break

35. Geologic UpliftSimon Channel Evolution ModelSource:Simon, 1989, USACE 1990

38. Head Cut

46. IIIIIIIIIIIIIIIIIIIIVIIIIOriginal NickpointIVVIVI

47. G4c Alabama

48. Changes in Sediment LoadDevelopment

49. Agriculture

50. Bank Erosion

51. Impoundments

52. Aggradation

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

58. Debris OccurrenceLarge Woody Debris

59. Depends on Riparian Stability

60. Beaver DamsWoody debris

61. ImpoundmentsUpstream:Decrease velocities

62. Deposition of fine material

63. Loss of habitatDownstream:“Hungry water”

64. Change in flowRiparian Condition (Buffer)Composition

65. Density

66. PotentialValues of VegetationHabitatsWater QualityBank StabilityShade & FoodStream Corridor Restoration: Principles, Processes, and Practices, 10/98, by the Federal Interagency Stream Restoration Working Group (FISRWG)."

67. Streamside Forests (also known as riparian buffers)Trees, shrubs, herbs, and grasses are critical to the health of streams

68. Buffers are the first line of defense against the impacts of polluted runoff

69. natural vegetation buffers are especially critical in urban areas

72. Altered States Due to DisturbanceChannelization

73. Straightening

74. Levees

75. Hardening

76. MiningFloodplain Filling

78. Stability Assessmenthttp://www.epa.gov/warsss/index.htm

79. Entrenchment Ratio

80. Lateral StabilityMeander Width Ratio

81. Bank Erosion (BEHI)G4c Alabama

82. Stream Channel Succession (WARSSS)

83. Stream Channel Succession (WARSSS)http://www.epa.gov/WARSSS/sedsource/successn.htm

84. Stability Assessmenthttp://www.epa.gov/warsss/index.htm

85. Entrenchment Ratio

86. Lateral StabilityMeander Width Ratio

87. Bank Erosion (BEHI)Meander Width RatioMWR = Wblt / WbkfWblt = Belt WidthWbkf = Bankfull Width of Riffle Cross-SectionWbkfWblt

88. Bank ErosionMonitoring

89. Bank Erosion Hazard Index (BEHI)

90. Bank Erosion Hazard Index (BEHI)

91. Bank Erosion Hazard Index (BEHI)

92. Bankfull Stage: Water fills the active channel and begins to spread onto the floodplainStream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.

94. Bank Height RatioVery Low

95. Bank Height RatioModerate

96. Bank Height RatioVery High

98. Root Depth RatioVery Low BEHI