Stream Habitats and Spatial Scale

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Stream Habitats and Spatial Scale
Drainage Network gt10 km 10,000 yrs
Segment 1 km 100 1000 yrs
Reach 100 1000 m 10 100 yrs
Channel Unit 10 100 m 1 10 yrs
Microhabitat 1 10 m 1 day 1 year
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Stream Habitats and Spatial Scale
Stream Segment Stream section bounded upstream
and downstream by the confluence of a perennial
tributary. Stream Reach Section of stream
within a stream segment that is 30-40x the mean
stream width. Should contain 3-4
pool-riffle-pool sequences and / or 3-4 meander
bends. (Focal scale of the Rosgen
approach) Hydraulic Channel Unit Relatively
homogeneous area within a stream reach that
differs significantly in depth, flow, and/or bed
composition from adjacent areas. To be
considered an HCU, the area must be at least as
long as 1 mean stream width. Microhabitat
Relatively homogeneous area within a hydraulic
channel unit that differs significantly from
surrounding areas. Considered to be the scale at
which most aquatic organisms make habitat
selection decisions.
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Major Watersheds of West Virginia
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Lower Cheat SubBasin
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Little Sandy River and Muddy Creek Watersheds
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Segment of Cheat Between Albright and Muddy Creek
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Reach of Cheat River near mouth of Muddy Creek
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Hydraulic Channel Unit (high gradient riffle /
rapid) of Reach of the Lower Cheat River at Base
of Narrows
High Velocity Microhabitat
Low Velocity Microhabitat
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Hydraulic Channel Units
Riffle
Run
Glide
Pool
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HCU Classification Hawkins et al. (1993)
Slow Water
Fast Water
Scour Pools
Dammed Pools
Turbulent
Non-Turbulent
Eddy Trench Convergence Lateral Plunge
Falls Cascade Rapids Riffle Chute
Sheet Run
Debris Beaver Landslide Backwater Abandoned
Channel
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CHANNEL UNIT CLASSIFICATION Petty et al. (2002)
Low Gradient / Slow
High Gradient / Fast
Narrow
Wide
Narrow
Wide
Non-Complex
Complex
Non-Complex
Complex
Non-Complex
Complex
Non-Complex
Complex
Pocket Water
Glide
Run
Low Gradient Riffle
Bluff Pool
High Gradient Riffle
Bluff Pool / Run Complex
Pool
Riffle / Run Complex
Complex high microhabitat scale variability in
depth, current velocity, and substrate composition
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GLIDE Homogeneous, intermediate depth, slow
velocity, no surface agitation, usually follows a
pool and leads into a riffle
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RIFFLE Shallow, high gradient, heterogeneous
velocity and substrate, surface agitation,
usually follows a glide and leads into a run
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RUN Deep, high velocity, little to no surface
agitation, heterogeneous substrate, usually
follows a riffle and leads into a pool
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POOL Deep, low velocity, surface agitation, small
diameter substrate, usually follows a run and
leads into a glide. Functionally the most
important HCU. Formed by a variety of processes
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Pool Types and Pool Forming Elements (PFEs)

• POOL TYPES
• Dammed PD
• Lateral Scour PL
• Mid-Channel Scour (Trench) PT
• Plunge PP
• Backwater PB

• PFES
• Rootwad RW
• Boulder / Bedrock BD
• Large Woody Debris WD
• Unknown Fluvial FL

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Plunge Pool / Bedrock
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Plunge Pool / Large Woody Debris
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Lateral Scour Pool / Bedrock Wood
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Trench Pool / Boulder
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ROLE OF HABITAT COMPLEXITY
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Less Complex
More Complex
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WHY IS HABITAT COMPLEXITY SO IMPORTANT?

• Ecological function varies among channel unit
  types.
• Habitat complexity increases retentiveness and
  the ability of a stream to convert detritus to
  biomass and cycle nutrients locally.

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Microhabitat Characteristics of HCUs

• Things that get measured
• Average Current Velocity
• Bottom Current Velocity
• Depth
• Substrate Compositition
• Distance to Cover and Cover Type

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Microhabitat Characteristics of HCUs
Depth Boulder Silt
Bluff Pool
Riffle / Run Complex
Glide
Dist. to Cover Cobble Gravel
Int. Gradient Riffle
Low Gradient Riffle
Sand Silt
Current Velocity
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Microhabitat Characteristics of Channel Units
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Habitat Suitability Curves (Brook Trout)
12cm
20cm
5cm
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Trout Habitat Suitability
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THE PRIMACY OF STREAMSIDE VEGETATION
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Functional Roles of Vegetation

• Mediate Storm Flow
• Sediment Control
• Bank Stability
• Shading
• Nutrient Inputs
• Organic Matter Inputs (DOM and CPOM)
• Large Woody Debris Inputs
• Pool Formation and Habitat Complexity
• Sediment, Organic Matter and Nutrient Retention
• Aquatic Insect Habitat

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Plunge Pool / Large Woody Debris