Greg Jennings, PhD, PE Professor, Biological & Agricultural Engineering

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

2. Stream Stability • What is Stability? • Causes of Instability • 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. 10% 50% Development Impacts on the Water Cycle 55% 15% Courtesy NEMO, Univ. of CT

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

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

10. Hydrologic Responses to Urbanization Increased discharge Increased peak discharge Increased velocities Shorter time to peak flow More frequent bankfull events Increased flooding Lower baseflow 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. I I I I I I I II II I I III III IV I III Original Nickpoint IV V I VI

46. G4c Alabama

47. Stream Channel Succession (WARSSS)

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

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

50. Entrenchment Ratio