Stream Processes

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Stream Processes
Andy Ward The Ohio State University
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Stream Behavior Is Predictable

• Streams seek a state of dynamic equilibrium
• Equilibrium is a function of the flow and
  sediment
• Equilibrium is naturally associated with a main
  channel and a flood-prone area
• Effective (bankfull) discharge forms the main
  channel
• Streams meander in a predictable manner

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Stream Stability

• Natural stream channel stability is achieved by
  allowing the river to develop a stable dimension,
  pattern and profile such that channel features
  are maintained and the stream system neither
  aggrades nor degrades (Leopold)
• Correctly engineered rigid channels can be part
  of a stable stream system.

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River Dimensions
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Velocity Distribution In A Channel
Depth-averaged velocity is above the bed at about
0.4 times the depth
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Deep Overbank Flow
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Features Of A River
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Salt Creek (Hocking County Ohio)
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Flow in Streams

• Effective Discharge
• Shear Stresses
• Sediment Transport
• Bed Load Movement
• Land Use and Land Use Change
• Open Channel Hydraulics
• Resistance Equations
• Compound Channel
• Pattern Profile

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Effective Discharge

• The effective, dominant, and bankfull discharge
  are often considered as synonymous.
• The bankfull discharge is considered to be the
  channel-forming or effective discharge (Leopold,
  1994).
• The bed load fraction of the total sediment load
  is most influential in channel forming processes
  and effective discharge (Emmett and Wolman,
  2001).
• The effective discharge typically occurs less
  than a hand full of times annually

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Bankfull Depth Versus Discharge
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Effective Discharge
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Bed Material is Predictable
Bed Material
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Shear Stresses on the Bed and Bank
Mean bed material size is a function of the shear
stresses produced by the effective (critical)
discharge
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Andys 1 x 1 1 Rule

• A 1 ft flow depth and a 1 bed slope can move 1
  inch diameter bed material
• A 4 ft flow depth and a 0.5 bed slope can move
  2 inch diameter bed material
• (d50 approximately 2inch)

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Shear Stress on Banks

• On straight banks they are 0.7 - 0.8 the mean
  bed shear stress
• On bends they are 2-4 times the mean bed shear
  when the ratio of the radius of curvature to
  width is less than 5

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Bed Material Particle Sizes
Based on a Wolman Pebble Count
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Sediment Transport
Types

• Wash Load
• Suspended Load
• Bed Load

Methods

• Shear Stress
• Power
• Parametric

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Meanders
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Meander Length vs Channel Width
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One meander length is equal to 10-14 Bankfull
Widths
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Meander Geometry
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Meandering adjusts the slope for the best
stability.
Meandering
Starts Here
Ends Here
Slope rise / run
Straighter, Steeper, Faster
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Flood Hydraulics within a Meander
Sellin and Willetts, Floodplain Processes,
Walling, 1996
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Streamway Concept
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Drainage Area 30 sq. mi. Streamway
120 DA 0.43 518 ft
518
1997
1980
1966
1951
1989
Salt Creek Vinton County, Ohio
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Channel Features Profile (Slope)
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Pools and Riffles
Riffle - Pools Features (Spaced at 5-7 Bankfull
Widths)
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Stream Changes Are Predictable
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Channel Evolution
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Bank Erosion Hilliard, Ohio
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Loss of Stream Equilibrium

• Lost Floodplain Access
• Channel Resizing
• Loss of Buffering from Small Streams and
  Floodplains

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Thank You!