Stream Classification Why classify Why classify 1 a
- Slides: 71
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 C C Channel Head C C Colluvial Channels 1. Earth Flows 2. Gully Erosion 3. Debris Flows Fluvial Channel Network
1. ) Earth Flow Terrain
Copyright © Martin Geertsema 2002
2. ) Gully Erosion
3. ) Debris Flow Terrain
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High Gradient, Confined Channels Cascades
High Gradient, Confined Channels Poorly organized cobble and boulder bed Tumbling flow over large, protruding grains gradient ≥ 7% Cascades
High Gradient, Confined Channels Step-Pool
High Gradient, Confined Channels Interlocking cobbles and boulders organize into discrete channelspanning stone lines that form alternating drops (steps) and pools. Gradient: 4 - 6% Step-Pool
High Gradient, Confined Channels Cascades Are they very responsive to change? Step-Pool
High Gradient, Confined Channels Cascades Are they very responsive to change? How / where do organisms seek refuge during flood events? Step-Pool
Moderate to Low Gradient, Unconfined Channels Plane Bed Pool Riffle
Moderate to Low Gradient, Unconfined Channels Plane Bed Pool Riffle Are they sensitive to changes in sediment & wood supply and/or discharge? How / where do organisms seek refuge during floods?
Moderate to Low Gradient, Unconfined Channels Plane Bed Pool Riffle Are they sensitive to changes in sediment & wood supply and/or discharge? How / where do organisms seek refuge during floods?
Moderate to Low Gradient, Unconfined Channels Pool Riffle
Moderate to Low Gradient, Unconfined Channels Bedforms: alternating bar / pool Plan form: sinuous Gradient: < 2% Pool Riffle
Copyright © Norm Catto 2002
Convergent Flow (flow concentrates in pools causing scour) Divergent Flow (flow spreads out toward banks in riffles) Pool
Convergent Flow (flow concentrates in pools causing scour) Divergent Flow (flow spreads out toward banks in riffles) Pool secondary circulation Pool
Convergent Flow (flow concentrates in Pools causing scour) Divergent Flow (flow spreads out toward banks) Pool Flow Reversal Concept -During low flows velocity is higher in riffles -During high flows velocity is highest in pools.
Where do organisms seek refuge during high flows?
Where do organisms seek refuge during high flows? Floodplain Habitats
Copyright © Richard Kesel 2002
Moderate to Low Gradient, Unconfined Channels Plane Bed
Moderate to Low Gradient, Unconfined Channels relatively featureless gravel / cobble bed streams homogeneous habitat 2 – 4% slope Plane Bed
Alternating Bars and Pools In Sinuous Channels
Plane-Bed Channels
‘Forced’ Pool Morphology
Wood can also ‘force’ a pool-riffle morphology in otherwise plane-bed or bedrock reaches.
Braided Streams
Extremely Low Gradient, Unconfined Channels Dune Ripple
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)
hillslope High Transport Capacity channel head colluvial cascade Depositional Reaches step-pool plane-bed pool-riffle dune-ripple Montgomery and Buffington, 1997
High Transport Capacity colluvial cascade Depositional Reaches step-pool Particle Size channel head Valley Confinement Channel Gradient hillslope plane-bed pool-riffle dune-ripple Montgomery and Buffington, 1997
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
Channel Slope Particle Size
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