stream classification. why classify? 1.) a means of understanding and describing the variation...
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Stream Classification
Why classify?
Why classify?
1.) a means of understanding and describing the variation within and among streams
2.) a way to select comparable sampling sites
3.) a way to interpret a broader context for how we can extrapolate information gathered at specific sites
4.) an approach for assessing past and possible future states
Process-Based Approach
Process-Based Approach
Streams classified the same not only look similar, they are formed by similar processes.
Basic premise is that streams with similar form (and formative processes) will function similarly.
‘Colluvial’ vs. ‘Alluvial’
Colluvial: unorganized and poorly sorted deposits at the base of a hillslope, formed by gravity.
Alluvial: formed by the action of flowing water, indicated by rounded rocks, distinct channel banks, and organized bed forms.
‘Colluvial’ vs. ‘Alluvial’
Colluvial: unorganized and poorly sorted deposits at the base of a hillslope, formed by gravity.
Alluvial: formed by the action of flowing water, indicated by rounded rocks, distinct channel banks, and organized bed forms.
Colluvial Channel
Why are colluvial channels important for alluvial river
ecosystems?
Why are colluvial channels important for alluvial river
ecosystems?• Comprise >80% of the channel network
• Major pathway for the routing of water, sediment, organic matter, and thermal energy to downstream areas
• Unique and/or predator-free habitats for numerous amphibians and invertebrates
Process Domains
Channel Head
Colluvial Channels1. Earth Flows2. Gully Erosion3. Debris Flows
Fluvial Channel Network
C CC
C
1.) Earth Flow Terrain
Copyright © Martin Geertsema 2002
2.) Gully Erosion
3.) Debris Flow Terrain
• [insert video clip]
Cascades
High Gradient, Confined Channels
Cascades
High Gradient, Confined Channels
Poorly organizedcobble and boulder bed
Tumbling flow over large,protruding grains
gradient ≥ 7%
Step-Pool
High Gradient, Confined Channels
Step-Pool
High Gradient, Confined Channels
Interlocking cobbles and boulders organize into discrete channel-spanning stone lines that form alternating drops (steps) andpools.
Gradient: 4 - 6%
Cascades
Step-Pool
High Gradient, Confined Channels
Are they very responsive to change?
Cascades
Step-Pool
High Gradient, Confined Channels
Are they very responsive to change?How / where do organisms seek refuge during flood events?
Plane Bed Pool Riffle
Moderate to Low Gradient, Unconfined Channels
Plane Bed Pool Riffle
Moderate to Low Gradient, Unconfined Channels
Are they sensitive to changes in sediment & wood supply and/or discharge?How / where do organisms seek refuge during floods?
Plane Bed Pool Riffle
Moderate to Low Gradient, Unconfined Channels
Are they sensitive to changes in sediment & wood supply and/or discharge?How / where do organisms seek refuge during floods?
Pool Riffle
Moderate to Low Gradient, Unconfined Channels
Pool Riffle
Moderate to Low Gradient, Unconfined Channels
Bedforms: alternating bar / pool
Plan form: sinuous
Gradient: < 2%
Copyright © Norm Catto 2002
Convergent Flow(flow concentrates inpools causing scour)
Divergent Flow(flow spreads out
toward banks in riffles)
Pool
Pool
Convergent Flow(flow concentrates inpools causing scour)
Divergent Flow(flow spreads out
toward banks in riffles)
secondarycirculation
Pool
Pool
Convergent Flow(flow concentrates inPools causing scour)
Divergent Flow(flow spreads out
toward banks)
Flow Reversal Concept-During low flows velocity
is higher in riffles-During high flows velocity
is highest in pools.
Pool
Pool
Where do organisms seek refuge
during high flows?
Where do organisms seek refuge
during high flows?
Floodplain Habitats
Copyright © Richard Kesel 2002
Plane Bed
Moderate to Low Gradient, Unconfined Channels
Plane Bed
Moderate to Low Gradient, Unconfined Channels
relatively featurelessgravel / cobble bed streams
homogeneous habitat
2 – 4% slope
Alternating Bars and Pools
In Sinuous Channels
Plane-Bed Channels
‘Forced’ Pool Morphology
Wood can also ‘force’ apool-riffle morphology in otherwise plane-bed or bedrock reaches.
Braided Streams
Dune Ripple
Extremely Low Gradient, Unconfined Channels
Bedrock Channels
Why are there bedrock channels?
Why are there bedrock channels?
Sediment transport exceeds sediment supply
Grain size of sediment is small relative to the transport capacity (channel slope * drainage area)
Montgomery and Buffington, 1997
hillslope
channel head
colluvial
cascade
step-pool
plane-bed
pool-riffledune-ripple
High Transport Capacity
Depositional Reaches
Ch
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Gra
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Particle S
ize
Montgomery and Buffington, 1997
Valley C
onfin
emen
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hillslope
channel head
colluvial
cascade
step-pool
plane-bed
pool-riffledune-ripple
High Transport Capacity
Depositional Reaches
Channel Type-- Colluvial channels (>10%)-- Cascade (7-10%)-- Step-Pool (3-7%)-- Plane-Bed (1.5-3%)-- Pool-Riffle (<1.5%)
Ecological Implications of Different Channel Types
Channel Types & Bed Mobility
Cascade and Step Pool channels typically have an abundance of large, interlocking boulders that limit bed mobility. Benthic organisms can seek shelter in interstitial spaces.
Plane Bed and Pool Riffle channels typically have mobile beds during large floods. Benthic organisms can seek shelter in less mobile areas of the channel.
Dune Ripple channels are fully mobile during most storms. Benthic organisms may be limited to wood.
Spatial Extent of Fish
Abundance of Spawning Sites
Copyright © William Locke 2002
Ch
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Slo
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artic
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Size
