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

Classification Schemes Wolman and Miller Method Rosgen Method Montgomery and Buffington Method

Leopold and Wolman Classification

Wolman and Miller Classification Channel Patterns ….in plan view (bird’s eye) Straight Meandering Braided Transition between Straight And Meandering is when Sinuosity is 1.5

(pools and riffles) Riffles are spaced ~ 5-7 times the channel width

(pools and riffles)

` (pools and riffles)

Rosgen Method

Stream Succession…..

Strengths and Weaknesses of Rosgen Method…..

Montgomery and Buffington Method

“Process-Based Approach” Montgomery and Buffington Method “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.

High Transport Capacity hillslope channel head colluvial cascade Depositional Reaches step-pool plane-bed pool-riffle dune-ripple Montgomery and Buffington, 1997

‘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 Channel Head Colluvial Channels 1. Earth Flows 2. Gully Erosion 3. Debris Flows Fluvial Channel Network

1.) Earth Flow Terrain

Copyright © Martin Geertsema 2002 Earthflow at confluence of Muskwa and Chisca rivers, northern British Columbia. Copyright © Martin Geertsema 2002

2.) Gully Erosion Gulley erosion in cohesive soils and especially post-fire

3.) Debris Flow Terrain

DEFINE LANDSLIDES.

DEFINE DEBRIS FLOWS.

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 channel- spanning 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

High Transport Capacity hillslope channel head colluvial cascade Depositional Reaches step-pool plane-bed pool-riffle dune-ripple Montgomery and Buffington, 1997

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 Plane Bed

Moderate to Low Gradient, Unconfined Channels relatively featureless gravel / cobble bed streams homogeneous habitat 2 – 4% slope Plane Bed

Plane-Bed Channels

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

Sebaskachu R (Labrador) - tortuous meandering river developed on marine silt and fine sand. Copyright © Norm Catto 2002

toward banks in riffles) Convergent Flow (flow concentrates in pools causing scour) Pool Divergent Flow (flow spreads out toward banks in riffles) Pool

toward banks in riffles) Convergent Flow (flow concentrates in pools causing scour) Pool secondary circulation Divergent Flow (flow spreads out toward banks in riffles) Pool

Convergent Flow Divergent Flow Flow Reversal Concept (flow concentrates in Pools causing scour) Pool 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

Where do organisms seek refuge during high flows?

Where do organisms seek refuge during high flows? Floodplain Habitats

Copyright © Richard Kesel 2002 Meandering river, Alaska. Copyright © Richard Kesel 2002

Alternating Bars and Pools In Sinuous Channels

‘Forced’ Pool Morphology

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)

High Transport Capacity hillslope channel head colluvial cascade Depositional Reaches step-pool plane-bed pool-riffle dune-ripple Montgomery and Buffington, 1997

Valley Confinement Channel Gradient Particle Size High Transport Capacity hillslope channel head colluvial Valley Confinement Channel Gradient Particle Size cascade Depositional Reaches step-pool 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.

Channel Slope Particle Size

Discuss SPI and transition from bedrock to alluvial reaches [insert figure]