Components of a Natural Stream

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Components of a Natural Stream
Floodplain
Riparian Zone
Stream Channel
Surface Water Stream Bed Hyporheic Zone
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Riparian Zone Plant communities contiguous to and
affected by surface and subsurface hydrological
features of perennial and intermittent
waterbodies. Usually limited to the band of
vegetation that has a direct influence on the
structure and function of the active channel.
Floodplain gt Riparian Zone
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Floodplain lt Riparian Zone
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Stream Channel
Surface Water
Bed Surface
HYPORHEIC ZONE region of alluvial sediment
within the stream channel that lies immediately
below the bed surface and above bedrock. Can
vary in depth from 1 to several feet.
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Components of a Natural Stream
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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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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
Simple
Complex
Simple
Complex
Simple
Complex
Simple
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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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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• RIFFLES
• Accumulate FPOM
• FPOM eaten by most insects and some fishes
• Detritus converted to biomass (insects and small
  fish)
• Biomass exported to pool (trout food)

• POOLS
• Accumulate CPOM
• CPOM Decomposes ( shredding insects, bacteria and
  fungi)
• Transported downstream as FPOM

• RIFFLES
• Important areas of primary productivity
  (periphyton).
• Important areas of nutrient uptake and cycling.
• Site of most aquatic insect production.
• Foraging and spawning habitat for benthic fishes.
• FPOM and Periphyton are converted to biomass
  (bugs) and exported into pools.

• POOLS
• Provide cover for fishes during high and low flow
  events.
• Provide cover from predators.
• Provide thermal refugia during hot and cold
  periods.
• Spawning habitat for trout, chubs, and suckers.
• Foraging habitat for trout and other drift
  feeding fishes.

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Functional Roles of Riparian 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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