Physical Stream Habitat

What is “Habitat”?

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”

What is “Physical Habitat”?

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

Stream Morphology

Aquatic Community

Physical Habitat

Chemical HabitatInterspecies Interactions

Land Use Vegetation

HydrologicConditions

GeologyTopography

Measurable Characteristics of Physical Habitat

• 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 fine-sediments

• 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 CorridorRestoration, 199x

Scalar Unit DefinitionRole in Habitat

Characterization

Watershed Basin

Area defined by topography that contributes water and sediment to the stream network

Determines boundary conditions within which river operates

Segment Physiographically defined unit, based on relief, morphology and landscape position

Determines boundary conditions within which river operates

Reach Type Length of channel with uniform constraints resulting in a specific assemblage of geomorphic units

Describes channel planform and geometry

Geomorphic Unit

Fluvial channel forms representing distinct form-process associations

Determines channel character and behavior

Habitat Type Patches of relatively uniform flow and substrate characteristics

Describes ecologically relevant hydraulic and substrate conditions

LargeScale

FineScale

Heirarchical Classification System

103 m 102 m 101 m 100 m 10-1 m

Watershed Segment Reach Type GeomorphicUnit

MicrohabitatType

How is each scale important to the species of interest?

Temporal Variability incorporates ‘predictable’ and ‘unpredictable’ cycles

Macroinverts

Salmon

Physical habitat a function of processes operating at multiple spatial and temporal scales

How do we objectively assess it?

Define Stream Habitat Types (Classification)

• 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

Mechanics of Habitat Formation

• Shear Stress/Velocity Reversal Hypothesis

• Helical Flow

• Contraction/Expansion of Flow

t = rghs v ~ f(Rs)

Knighton, 1998

Helical flow in meander bends

Knighton, 1998

Flow contraction and expansion

Wohl, 1998

Increased roughness reduces shear, promoting deposition of finer material

McBain & Trush, 2004

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

What promotes Habitat Diversity?

Disturbance

• Natural flow regime

• Varying sediment inputs

• Structural diversity - LWD

Natural stream systems are subject to the full spectrum of spatial & temporal disturbances

Episodic Sediment Transport

Natural Flow Regime

• 5 characteristics: Frequency

Magnitude

Duration

Timing

Rate of Change

• Key factor = extremes included

Disturbance acts to ‘reset’ processes

Mount, 1995

Large Woody Debris

• Increases local scour and deposition

• Provides structural habitat

• Transient nature (moves, breaks, clumps, decays)

All add to habitat diversity and complexity

Buffington & Montgomery 1999

Plane Bed

Wood-poorPool-riffle

Buffington & Montgomery 1999

Wood-richPool-riffle

Stream habitat diversity maintained over time

Species adapt

• Salmon – spawning and run timing

• Foothill Yellow-legged Frog – oviposition timing

• Cottonwood regeneration – accidental forest

Movement to Feed

Movement to Refuge

Movement to Spawn

Movement to Spawn Movement to Feed

Refugia from harsh environmental

conditions (e.g., extreme temperatures

or flows) with unfavorable growth

conditions

Spawning habitat with incubation

of eggs

Mosaic of feeding habitat(s)

with favorable growth conditions

Habitat 2

Habitat 1

Habitat

3

Redrawn by Bledsoe from Schlosser (1995)Diversity in Trout Habitat

Alterations to flow regime & sediment supply alter habitat diversity & biodiversity

Stream Corridor Restoration, 1998

Alterations to Stream Systems

• Flow extraction – diversions – groundwater

withdrawal

• Flow augmentation– ag runoff– hydropower

• Sedimentation – development – logging– mining

• Sediment Loss– dams– mining

• Channel Bed Coarsening• Loss of Fines/Gravels• Vegetation Encroachment• Low bed mobility

Degradation

• Channel Bed Fining• Excess Fines/Gravels• Lack of vegetation• High bed mobility

Aggradation

Effect of Dams

• 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

What can we do to improve spawning habitat conditions

downstream of dams?