Streams Rank Process

Calculate an individual stream score
Calculate a watershed or subwatershed stream rank

Calculate an individual stream score

The stream evaluation as a component of the watershed ranking is based on the following series of yes/no questions The answers must be based on "data", the results of a structured series of measurements, as opposed to occasional observations and opinion. If little or no data is available for a waterbody, and/or the data is no longer representative, then no ranking should be awarded and a recommendation for monitoring should be made. Stream system habitat rating forms filled out during stream classification is an example of structured data.

Download a Stream Evaluation Worksheet

Does this stream have the potential to positively respond and/or be protected if NPS controls are implemented?

This question is intended to limit the ranking to streams degraded or threatened by nonpoint sources. If there is no threat or degradation from NPS pollutants, the ranking process need not be continued.

If NO, the stream receives a low rating - stop the survey.

If YES, continue survey by answering the questions below.

A High Stream Rating

A positive response to any one of the following questions results in a high rating for the stream (documentation using data, as described above, is necessary for this rating).

Endangered Resources

1. Does the stream provide a unique environment for an endangered or threatened species (Bureau of Endangered Resources).

Fishery

2. Is the population and diversity (predominance of pollution tolerant species) less than optimal due to water quality and or habitat degradation?

The intent here is identifying fishery populations substantially lower than the stream should be able to support. For example, Elk Creek Watershed supported only a few trout per mile, a small fraction of the population potential. The professional judgment of the fisheries manager should be used to determine when the population is at a level substantially less than optimal.

3. Does the stream exhibit recurring fish kills?

Water Chemistry

4. Do any of the following occur on a widespread and habitual basis?

• dissolved oxygen standard violations (especially event-related);
• ammonia standard violations (use standards);
• nitrate levels greater than 10 mg/l (federal and state standards for public drinking water);
• toxicity problems due to pesticides or other toxicants from NPS sources;
• mean suspended solid levels greater than 420 mg/l (federal guidance).

Macroinvertebrates

5. Is the Hisenhoff Biotic Index or Family Biotic Index rated poor or very poor?

Physical Habitat

6. Is there a high rate of streambed sedimentation (eg., is there evidence a gravel bottom once existed?);

7. Are negative physical changes (accelerated as compared to natural) to stream morphology occurring; eg., filling in of deep holes, stream becoming wider and shallower, chance in course?

Vegetation

8. Is there a predominance of undesirable vegetation (algae or macrophytes)?

Threatened streams

Threatened streams are rated high. Determining threatened status requires an interpretation of available data to discern downward trends and/or the beginning of use impairments in any of the criteria listed above.

For example, a stream otherwise rating "medium" due to rare dissolved oxygen violations, is rated "threatened" if previous monitoring indicated no dissolved oxygen violations. If a Class I trout stream is affected by increased sediment loading, it is threatened.

Medium Rating

• Fish populations of intermediate abundance or diversity;
• Occasional water quality standard violations or consistent borderline readings;
• Hilsenhoff Biotic Index of fair to fairly poor;
• Lesser but still greater than optimal levels of stream sedimentation;
• Lesser but still greater than optimal abundance of undesirable vegetation.

An additional factor influencing stream ranking are the outstanding and exceptional resource water designations.

If a medium-ranked stream is a threatened ORW or ERW, it moves to a high ranking

If a low-ranked stream is a threatened ORW or ERW, it moves to a medium ranking

Calculate a watershed or subwatershed stream rank

To receive a watershed stream rating, at least 50 percent of the total perennial stream miles must be rated based on data. For unnamed streams, include only those longer than five miles. If you are rating a subwatershed area, use the same logic that is used for a full-sized watershed, only apply the process to this smaller area. If adequate data exists to award a rating, use a weighted mean based on total stream miles in the designated area to calculate the watershed or subwatershed rating.

Each perennial named or unnamed stream in the watershed receives a rating. A high rating is worth 10 points; a medium, 5 points; a low or no rating due to inadequate or no data is 0 points. Remember, do not include unnamed streams shorter than 5 miles.

The final number from the worksheet is a stream-mileage weighted mean based on the number of stream miles in each category times the points awarded, divided by the total stream miles evaluated in the watershed:

Stream Example To help you keep track of your scores, you can set up a table with the following categories: Stream, Miles, Data (Y/N), Use Problem(Source/Impact), Rank Points, Total Points.

Thus, the total score of 275 divided by the total stream miles of 71 would leave a stream subwatershed score of: 3.87