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Understanding Stream Channel Stability: Dynamics, Causes, and Assessment Methods

This article explores the nature of stable stream channels, focusing on how a stream transports sediment while maintaining consistent dimensions, patterns, and profiles over time without significant aggradation or degradation. We analyze factors that dictate stability, including valley morphology, hydrology, and sediment supply, alongside causes of channel instability, such as altered hydrology and land use changes. Additionally, we highlight assessment methods for channel stability using Pfankuch's evaluation metrics and Rosgen's river classification.

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Understanding Stream Channel Stability: Dynamics, Causes, and Assessment Methods

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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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