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Rock Riffle Design Course

Learn how to balance human activity with nature, reduce sediment, protect infrastructures, and improve aquatic habitats through rock riffle grade control structures. Understand channel dynamics, stability factors, and optimal riffle spacing for effective streambank restoration.

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Rock Riffle Design Course

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  1. Rock Riffle Design Course

  2. Goals of Streambank Restoration • Work With Nature • Reduce Sediment • Protect Cropland • Protect infra-structure • Improve Water Quality • Improve Aquatic Habitat • Make it Affordable

  3. Lanes Balance

  4. 200+ years of Human Activity on the Landscape • Cleared the Timber • Plowed the Prairie • Drained the Wetlands • Straightened the Streams • Leveed the Floodplains • Built Cities with Large Areas of Concrete, Asphalt and Rooftops

  5. Results of Human Activity on Stream dynamics • Increased Runoff • Increased Stream Slope • Reduced Floodplain Width

  6. Design Philosophy • Work WITH the Natural Processes. • Know Where Nature is Taking the Stream. • Determine the Cause of The Problem • Treat Only the Cause • Let Nature Finish Healing The Banks • Keep the Cost Down

  7. Channel Evolution Model (CEM)

  8. Stream Stabilization Techniques • 4 Major Practices Used in Illinois =========================== • Rock Riffle Grade Control Structures (stage II or III) • Stone Toe Protection (stage III or IV) • Bendway Weirs (stage IV) • Stream Barbs (stage IV)

  9. Rock Riffle Grade Control Structures (stage II/ III streams) • Stabilize the Bed • Creates Riffle/Pool Sequence • Dissipates Energy • Aerates Water • Permit Fish Passage • Aesthetically Attractive

  10. Determine Stability • Review I & E Data • CEM Stage? • Entrenchment Ratio?

  11. McCray Stream Site • Valley slope = 0.0028 • Surveyed slope ave. 0.0024 (slightly lower) • Bed in Riffle ---Clay (exposed in riffle bed) • Width/Depth ratio = 10.3 (just over 10) • Entrenchment Ratio = 1.28 (just under 1.4) • 2 elements suggest Grade Control • 2 elements outside suggested range (barely)

  12. Channel Geometry Considerations • Sine Wave Flow • Anticipated Scour Depth • Radius Curvature/Bankfull Width Ratio (should be more than 1.8) • Existing Riffle Location • Existing Riffle Spacing

  13. Scour Depth • Assume Scour Depth will equal Max. Bankfull Flow Depth • Assumes bed material allows full Sine Wave Flow to develop over time

  14. Radius of Curvature • Ave radius = 2.3 times bankfull width (Leopold) • Range generally from 1.6 to 4.5 times bankfull width (natural streams) • 2.3 is the optimum for hydraulic efficiency • 1.8 is the suggested minimum under guidelines

  15. Locating Riffles • 5 to 7 Bankfull widths (28 ft) • Expect Spacing--140 to 196 ft. • Located at Cross-over Points

  16. Read The Channel • Knickzones and Headcuts • May be hundreds of feet long • Little or no bedload in crossover pts. • Will not be bedload material (sand wave) • Increasing bank height downstream? • Stable Points? (Bedrock, Culvert, etc)

  17. Gather Survey Data • Bed Profile • Water Surface Profile • Typical X-Section @ Riffles (detailed) • Low Bank Profile • Stream Cross-over Points (Stations) or surveyed planform

  18. Plot profile • Channel Grade (riffle to riffle) • Riffle Spacing • Compare low bank vs. channel grade • Pool Depths • Stable Points

  19. Riffles

  20. Existing Riffles? • Stations: 0+00, 4+25, 5+90, 8+25, 10+20 • 11+50, 13+20, 13+75, 14+75 15+50,16+40, 20+20 • 12 riffles in 2020 ft. --Ave. Spacing 168 ft. • Max. Spacing --425 ft. • Min. Spacing-- 55 ft.

  21. Low Bank Grade Line Profile

  22. Bank Heights

  23. Plot Cross-Section(s) • Bankfull depths • Riffle Crest Elev.

  24. Determine New Gradeline • Slope (will be greater than existing slope) • Stable Upstream(flood out headcut/knickzone) • Stable Downstream(Culvert/Stable Grade, etc) • Blend into existing channel bed (generally 1.0 ft. height or less @ last riffle)

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