AQUATIC HABITAT CLASSIFICATION

Site Visit
Habitat Rating System
Substrate
Cover
Macroinvertebrates
Fish Assemblage
Classification
Next Step

(Figure 1 shows the steps in determining the aquatic habitat classification.)

(The referenced rule is Title 15A, Subchapter 2k, Section .0500 of the N.C. Administrative Code, see excerpt.)

The procedure for determining the minimum flow required to maintain aquatic habitat begins with an evaluation of the habitat in the affected reach downstream of the dam. The intent of this approach is to base the degree of resource protection provided by a minimum flow on the quality of that resource. The cost and time associated with conducting a field study to recommend a minimum flow will only be required where the quality of aquatic habitat is good or there is some other special resource value.

Site Visit

The aquatic habitat classification will be determined by the North Carolina Wildlife Resources Commission (WRC). Upon receipt of an application to construct, repair, or alter a dam, or upon notification that the minimum flow from an existing dam is under review, a District Fisheries Biologist or Habitat Conservation Biologist of the WRC will conduct a site visit to determine the aquatic habitat classification for the affected stream reach. The site visit will consist of a survey of the stream channel for the entire affected reach if the reach is relatively short such as a bypassed reach at a hydroelectric plant. If the affected reach is long, such as downstream of a water supply dam, then a representative reach will be surveyed. The location of the representative reach will be determined by the biologist, but will typically be in the vicinity of the first bridge crossing downstream from the dam. At this location, three bankfull width measurements will be taken. Bankfull width (BFW) is the distance across the channel between the points on each bank where woody vegetation begins. The average of the three measurements will be the BFW for the stream. The length of the representative reach to be surveyed will be equal to fifteen times the BFW.

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Habitat Rating System

Aquatic habitat will be divided into three classes, designated as "poor," "moderate," and "good." All streams will be classified as moderate aquatic habitat unless specific criteria are met to change the classification to good or poor. Determination of "good" or "poor" aquatic habitat classifications will be based on four criteria: substrate, cover, macroinvertebrates, and fish assemblage.

If the rating for an individual habitat criterion (substrate, etc.) is neither "good" nor "poor," it is considered "moderate." This can be thought of as a three point scoring system: "poor" being negative one, "good" being plus one, and "moderate" being zero. If the total score for substrate, cover, and macroinvertebrates is negative two or lower, then the fish assemblage is used to determine if the rating is "poor" or "moderate." If the score is plus two or higher, then the fish assemblage is used to determine if the rating is "good" or "moderate." Scores between negative one and plus one receive an overall rating of "moderate."

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Substrate

Substrate ratings will be determined by the percentage of silt, sand, gravel, cobble, boulder, and bedrock occurring in the representative reach. This determination will be made by a visual survey of at least four transects across the channel in the representative reach. These transects will be located at distances equal to 25, 50, 75, and 100 percent of the length of the reach. The percentage of each substrate type will be recorded for each transect and averaged for the reach. Substrate ratings will be:

Good - 50 percent or more is clean substrate with gravel or cobble.
Poor - 80 percent or more is silt, sand, or smooth bedrock.

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Cover

Cover ratings will be based on the quantity and diversity of cover objects present in the channel that could be utilized by fish. Cover includes small and large boulders, bedrock, undercut banks, woody debris, overhanging vegetation, and aquatic vegetation. Cover ratings will be:

Good - Widespread and diverse cover.
Poor - Rare or no cover.

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Macroinvertebrates

Macroinvertebrate ratings will be based on the Division of Water Quality's (DWQ) benthic macroinvertebrate database. If the stream or reach being rated is not in the database, then a macroinvertebrate survey following the Standard Operating Procedures for the Biological Assessment Group will be conducted. Macroinvertebrate ratings will be:

Good - A rating of good or excellent from the DWQ database or from a site-specific survey.
Poor - A rating of fair or poor from the DWQ database or from a site-specific survey.

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Fish Assemblage

If two out of three of the first three criteria (substrate, cover, and macroinvertebrates) are rated as "poor" or "good," then a fish assemblage rating will be determined. Fish assemblage ratings will be based on the North Carolina Index of Biotic Integrity (IBI) ratings contained in the DWQ database. If no rating exists for the stream or reach, then a fish assemblage survey to develop an N.C. IBI rating will be conducted. Fish assemblage ratings will be:

Good - A rating of good, good-excellent, or excellent from the N.C. IBI.
Poor - A rating of poor or less from the N.C. IBI.

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Classification

The aquatic habitat classification of the stream will be based on the ratings for substrate, cover, macroinvertebrates, and fish. A "good" classification requires good ratings for two out of three of the first three criteria plus a good fish assemblage rating. A "poor" classification results from a poor rating for two out of three for the first three criteria plus a poor fish assemblage rating.

Next Step

See Figure 3