Broad Definition (EPA):
“The spatial structure of the environment which allows species to live, reproduce, feed and move”
In Relation to Streams (USGS):
“The physical and chemical characteristics of a stream that determine suitability for habitation and reproduction of stream organisms”

“The template of water depth, water velocity, substrate, cover and temperature that supports the stream ecosystem” – USGS

Hydrologic
Conditions
Land Use
Geology
Topography
Vegetation
Stream Morphology
Physical Habitat
Chemical Habitat
Aquatic Community
Interspecies
Interactions

• Channel morphology / type
• Flow regime
• Sediment texture / mobility
• Bank structural features / stability
• Riparian condition and connectivity
• Physiochemical – temperature, DO, metals, nutrients, turbidity, etc.

Mill Creek

Salmon and trout habitat requirements include:
• adequate but not excessive stream flows
• cool well-oxygenated unpolluted water
• streambed gravels that are relatively free of finesediments
• adequate food supply
• instream structural diversity (interposed pools, riffles, hiding and resting cover)
Washington State Dept of Fish Wildlife

Physical stream characteristics affect stream organisms by defining:
• Habitat volume
• Habitat quality
• Disturbance magnitude
• Disturbance frequency

Habitat varies over spatial & temporal scales
Stream Corridor
Restoration, 199x

Large
Scale
Fine
Scale
Heirarchical Classification System
Scalar Unit Definition
Role in Habitat
Characterization
Watershed
Basin
Segment
Area defined by topography that contributes water and sediment to the stream network
Physiographically defined unit, based on relief, morphology and landscape position
Reach Type Length of channel with uniform constraints resulting in a specific assemblage of geomorphic units
Geomorphic
Unit
Fluvial channel forms representing distinct form-process associations
Habitat Type Patches of relatively uniform flow and substrate characteristics
Determines boundary conditions within which river operates
Determines boundary conditions within which river operates
Describes channel planform and geometry
Determines channel character and behavior
Describes ecologically relevant hydraulic and substrate conditions

Watershed
10 3 m
Segment
10 2 m
Reach Type
10 1 m
Geomorphic
Unit
10 0 m
Microhabitat
Type
10 -1 m
How is each scale important to the species of interest?

Salmon
Macroinverts
Temporal Variability incorporates
‘predictable’ and ‘unpredictable’ cycles

Physical habitat a function of processes operating at multiple spatial and temporal scales
How do we objectively assess it?

• Bisson et al, 1982
• McCain et al, 1990 (USFS)
• Hawkins et al, 1993 (USFS)
• Thomson et al, 2001 (UK, AUS)
Fish -
Centric

McCain et al, 1990

McCain et al, 1990
Bisson et al, 1982

Hawkins et al, 1993

Hawkins et al, 1993

McCain et al, 1990

Hydraulic Habitat
Flow types can be distinguished by velocity and depth using
Froude Number
F = v gd

Panfil & Jacobson, 2000

Thomson et al, 2001

Stream Habitat types are created and maintained by erosion and deposition of sediments.
Hjulstrom’s Diagram

• Shear Stress/Velocity Reversal
Hypothesis
• Helical Flow
• Contraction/Expansion of Flow

t = rghs v ~ f(Rs)
Knighton, 1998

Knighton, 1998

Wohl, 1998

McBain & Trush, 2004
Increased roughness reduces shear, promoting deposition of finer material

Diversity is a function of fluctuations in erosion and deposition processes over varying scales
Disturbance

Natural stream systems are subject to the full spectrum of spatial & temporal disturbances
• Natural flow regime
• Varying sediment inputs
Episodic Sediment Transport
• Structural diversity - LWD

• 5 characteristics :
 Frequency
 Magnitude
 Duration
 Timing
 Rate of Change
• Key factor = extremes included

Disturbance acts to ‘reset’ processes
Mount, 1995

• Increases local scour and deposition
• Provides structural habitat
• Transient nature (moves, breaks, clumps, decays)
All add to habitat diversity and complexity

Plane Bed
Wood-poor
Pool-riffle
Buffington & Montgomery 1999

Wood-rich
Pool-riffle
Buffington & Montgomery 1999

Stream habitat diversity maintained over time

• Salmon – spawning and run timing
• Foothill Yellow-legged Frog – oviposition timing
• Cottonwood regeneration – accidental forest

Spawning habitat with incubation of eggs
Movement to
Spawn
Refugia from harsh environmental conditions (e.g., extreme temperatures or flows) with unfavorable growth conditions
Movement to Spawn
Movement to Feed
Movement to Refuge
Movement to Feed
Mosaic of feeding habitat(s) with favorable growth conditions
Habitat
1
Habitat
3
Habitat
2
Diversity in Trout Habitat Redrawn by Bledsoe from
Schlosser (1995)

Alterations to flow regime & sediment supply alter habitat diversity & biodiversity
Stream
Corridor
Restoration,
1998

• Flow extraction
– diversions
– groundwater withdrawal
• Flow augmentation
– ag runoff
– hydropower
• Sedimentation
– development
– logging
– mining
• Sediment Loss
– dams
– mining

Degradation
• Channel Bed Coarsening
• Loss of Fines/Gravels
• Vegetation Encroachment
• Low bed mobility
Aggradation
• Channel Bed Fining
• Excess Fines/Gravels
• Lack of vegetation
• High bed mobility

• Block Sediment
• “Flatline”
Hydrograph
• Disrupt
Connectivity
• Channel Degradation bed coarsening, loss of fines/gravels
–
• Loss of extreme flows
(loss of disturbance) – low bed mobility, vegetation encroachment, low habitat diversity
• Block habitat access, alter water chemistry, shift from lentic to lotic system