Stream Classification Why classify Why classify 1 a

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