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A Stabile Stream Channel

A Stabile Stream Channel. The ability of a stream, to transport the sediment and flows produced by its watershed in such a manner that the stream maintains a consistent dimension, pattern, and profile over time without either aggrading or degrading (Rosgen, 1996).

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A Stabile Stream Channel

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  1. A Stabile Stream Channel • The ability of a stream, to transport the sediment and flows produced by its watershed in such a manner that the stream maintains a consistent dimension, pattern, and profile over time without either aggrading or degrading (Rosgen, 1996).

  2. Stable channel = consistent D,P and P over time

  3. (Sediment LOAD) x (Sediment SIZE) (Stream DISCHARGE) x (Stream SLOPE)

  4. What dictates D, P and P? • Valley morphology • width • Soils • Geology • Relief • Hydrology • History of sediment deposition

  5. Streams strive to achieve stability Change in Parameter Channel Instability Channel Adjustment

  6. Channel Evolution

  7. What Happens When….. • Channelize a stream segment? • Reduce sinuosity • Increase gradient • Downcutting within and upstream of area (degradation) • Deposition downstream (aggradation) • Changed dimension, pattern and profile

  8. Causes of Channel Instability • Altered hydrology • Changes in sediment supply • Channel alterations • Removal or conversion of streamside vegetation • Land use changes • Land cover changes

  9. A method to assess channel stability • Pfankuch (1975) Channel Stability Eval. • Upper bank (4 attributes) • Lower bank (5 attributes) • Stream Bed (6 attributes) • Adjust for stream type using Rosgen (1996)

  10. Upper Banks(Bankfull elev. to floodprone elev.) • Landform slope • Mass wasting or failure • Debris Jam potential • Vegetative bank protection

  11. Lower Bank(low flow water level to bankfull elev.) • Channel capacity (W:D) • Bank rock content • Obstructions, flow deflectors, sediment traps • Cutting • Deposition

  12. Stream Bed(below low flow water level) • Rock anularity • Brightness • Consolidation • Bottom size distribution • Scouring and deposition • Cling aquatic vegetation

  13. Sand Hill River SHR311 • F5 • Score 109 • Good

  14. Sand Hill River • F6 • Score 143 • Poor

  15. Sand Hill River • F5 • Score 109 • Good • F6 • Score 143 • Poor

  16. SHR311 • F5 • Score 109 • Good • LR1 • C4 • Score 103 • Fair

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