Stream Classification

What factors affect stream morphology? Width Depth Slope Velocity Discharge Flow resistance Sediment size Sediment load Leopold et al (1964)

Why classify?

Communication Tool Describe Existing Conditions & Trends Describe Restoration Goals Stream Classification Research Tool

Classification Schemes Wolman, Leopold and Miller/Schumm Method Montgomery and Buffington Method Rosgen Method

Leopold and Wolman/Schumm Classification

Wolman and Miller/Schumm Classification Channel Patterns (alluvial) ….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

Montgomery and Buffington Method

“Process-Based Approach” Montgomery and Buffington Method

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.

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

‘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?

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 Channels 1. Earth Flows 2. Gully Erosion 3. Debris Flows Fluvial Channel Network C C C C

1.) Earth Flow Terrain

Copyright © Martin Geertsema 2002

2.) Gully Erosion

3.) Debris Flow Terrain

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

Cascades High Gradient, Confined Channels

Cascades High Gradient, Confined Channels Poorly organized cobble 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) and pools. Gradient: 4 - 6%

Cascades Step-Pool High Gradient, Confined Channels Are they very responsive to change?

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

Plane Bed Pool Riffle Moderate to Low Gradient, Unconfined Channels

Plane BedPool 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 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 Channels

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

Braided Streams

Dune Ripple Extremely Low Gradient, Unconfined Channels

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-riffle dune-ripple High Transport Capacity Depositional Reaches

Channel Gradient Particle Size Montgomery and Buffington, 1997 Valley Confinement hillslope channel head colluvial cascade step-pool plane-bed pool-riffle dune-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%)

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.

Rosgen Method

Link to Wildland Hydrology

Link to website:

Rosgen Classification of Natural Rivers Based on physical characteristics (empirical) Requires field measurements Requires bankfull dimensions

Solving for the eight variables… Width Depth Slope Velocity Discharge Flow resistance Sediment size Sediment load Leopold et al (1964)

Four Primary Components of the Rosgen Method Dimension (cross-section) Pattern (plan form) Profile (bed form) Bed material (substrate)

Level One: Rosgen Classification

Level Two: Rosgen Classification

Level One: Rosgen Classification

Strengths and Weaknesses of Rosgen Method…..

Stream Succession…..