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 (birds 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 (