1. Module # 8 Channel Evolution Implications & Drivers of Instability
Iowa’s River Restoration Toolbox Level 1 / Base Training

4. Channel Evolution Models
Key Tool Used for Stream Assessments
Predictor of Current & Future Stream Stability
Useful for Prioritization of Restoration Activities
Useful to Inform Design

5. Channel Evolution Models
Simon’s Modification of Schumm’s Model

6. Shear Stresses in Streams
Discharge Return Interval
Shear Stress
Natural Stream
Channelized Stream
2-Year Storm
100-Year Storm
D100 D2
Channelized Stream
100-Year Storm
D100
2-Year Storm D2
Natural Stream

7. Use of Rosgen’s Classification System to Predict Channel Evolution
Shear stress drives the evolution process. If the depth of the 1st E cross section is d and the depth to the top of bank of the G cross section is 2d then shear stress doubles of the slope does not change at all. On the original E channel the same flood even would spread out on the floodplain and minimally increase shear stress….If we were considering restoring the F stream here, can use see how we could restore the stream and reduce flooding? Excavate a floodplain and construct a C that will evolve to an E stream at the existing elevation.
E  G  F  C  E

8. Use of Rosgen’s Classification System to Predict Channel Evolution
Often it is helpful to understand how the stream reached the state that it is in. Why would a stream go from a “stable C” to a G?...lowering of base control/elevation causing a head cut. Actual raising of the banks by and impoundment such as a mill dam. Alavulsion or channelizing that reduces the stream length and then effectively increases the stream slope, which increases the shear stress and stream power. More shear stress likely means bed and bank erosion if no controls are in place. Would like to add in profile with bend removed to illustrate increase in slope.

9. Use of Rosgen’s Classification System to Predict Channel Evolution
Source: D. L. Rosgen

10. Use of Rosgen’s Classification System to Predict Channel Evolution
Source: D. L. Rosgen

11. Use of Channel Evolution to Inform Design
Indicator of Risk of Instability
Future Sediment Loadings Predictions
Are Other Nearby Streams Headed for Instability
When Can Streams Stabilize on Their Own?
Temporary control has stopped the headcut. Insert headcut picture from Kleber?

14. Other Drivers of Instability
Floodplain Access
Bank Height Ratio
Entrenchment
Bed Stability/Headcuts
Planform Stability
Radius of Curvature
Meander Width Ratio
Pool to Pool Spacing
Riparian Corridor
Sediment Supply

15. Other Key Drivers Width to Depth Ratio Channel Length Channel Slope
Stream Type
Geomorphic Region/Geology
Bed Materials
Constraints

16. Module # 8 Channel Evolution Implications & Drivers of Instability
Iowa’s River Restoration Toolbox Level 1 / Base Training