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Habitat Assesment

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Habitat is the physical environment where an organism lives. Individual aquatic species have evolved to thrive in different niches of the stream but ultimately, a suitable habitat must be stable and provide food, shelter and protection from prey. The habitat assessment process involves 2 or more trained individuals rating ten stream parameters. The habitat parameters evaluated are related to overall aquatic life use and habitat absence or impairment may serve as a limitation for the aquatic biota.

Habitat Parameter Definitions

Bank Stability

Measures the existence of, or the potential for, detachment of soil from the upper and lower stream banks and its movement into the stream.

Bank Vegetative Protection

Measures the amount of the stream bank covered by vegetation which helps resist erosion and shade the stream.


Channel Alteration

Measurement of large-scale alteration of instream habitat that affects stream sinuosity and causes scouring. Examples of channel alteration are: artificial embankments, riprap, and other forms of artificial bank stabilization or structures, channelization of the stream, or presence of dams or bridges.


Channel Flow Status

The degree to which the channel is filled with water during base or average annual flow periods, judged by the vegetation line on the lower bank. A decrease in water will wet smaller portions of the streambed, thus decreasing available habitat for aquatic organisms.



The degree to which cobble, boulders, and other rock substrate are surrounded by fine sediment.


Epifaunal substrate/available cover

Physical features such as woody debris, root mats, leaf packs, and riffles that are available as shelter, feeding, spawning & nursery areas for aquatic organisms.


Frequency of Riffles

Estimates the frequency or occurrence of riffles which are a high-quality habitat supporting diverse populations of aquatic organisms.



A segment of the stream with little velocity. Commonly with water deeper than surrounding areas.



A shallow part of the stream where water flows swiftly over substrate (cobble/gravel rock or woody debris) to produce turbulence. A riffle area is characterized by three components: (1) a change in elevation, (2) oxygenation of the water, and (3) the riffle area is audible.


Riparian Vegetation Zone Width

Measures the width of natural vegetation from the edge of the upper streambank out through the floodplain. The Riparian Vegetation Zone serves as a buffer to pollutants entering a stream from runoff, controls erosion, and provides stream habitat and nutrient input into the stream.



A relatively shallow part of a stream with moderate velocity and little or no surface turbulence. A run usually connects a riffle and pool area.


Sediment deposition

Sediment influx from within the watershed and bank erosion may accumulate and cause an increase in the formation of islands and point bars, resulting in the filling of pools. High levels of sediment deposition create an unstable and continually changing environment that becomes unsuitable for many organisms.


Velocity/depth regime

High quality riffle/run prevelant streams are comprised of four combinations of velocity and depth: slow-deep, slow-shallow, fast-deep, and fast shallow.


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