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Rock Riffle Design Course

Rock Riffle Design Course. Goals of Streambank Restoration. Work With Nature Reduce Sediment Protect Cropland Protect infra-structure Improve Water Quality Improve Aquatic Habitat Make it Affordable. Lanes Balance. 200+ years of Human Activity on the Landscape. Cleared the Timber

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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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