Historically, compensatory mitigation for impacts to all aquatic systems was in the form of wetland mitigation. However, wetland mitigation does not provide appropriate replacement of aquatic functions lost due to impacts to fluvial systems. Because of this, many states now require that compensatory mitigation for impacts to stream resources in the form of restoration and/or enhancement of degraded stream channels utilizing natural channel design and bio-engineering techniques. Channel preservation of unique or otherwise ecologically important stream segments may also play an important role in mitigating stream impacts. Mitigation decisions are made during the permit review process. Mitigation requirements are often determined through site evaluations that document aquatic resource losses. (Source)

How streams are identified and assessed are not consistent practices across the United States. This web page provides links to resources that provide specific methods or approaches to identification and assessment.  For more information on practices in a specific state, please check out the State Summaries page on this site. 

Subjective, visual-based assessment protocols are rapid and relatively easy to use. They may provide an acceptable means of watershed-scale stream assessment or coarse level prioritization. However, they are rarely detailed enough to be used for project design, and their accuracy and precision has been subject to debate. In contrast, objective, quantitative assessments, often referred to as transect-based or measurement-based assessments, are time consuming and labor intensive. Detailed quantitative assessment is a prerequisite to project design and should be based on comparison to stable reference conditions. However, the precision of even some commonly utilized quantitative stream assessment metrics has been shown to be less than certain (Source)

EPA suggests that all stream protocols should have the following five characteristics:

  1. Classification: Stream assessment should be preceded by classification to narrow the natural variability of physical stream variables.
  2. Objectivity: The assessment procedure should remove as much observer bias as possible by providing well-defined procedures for objective measures of explicitly defined stream variables
  3. Quantitative Methods: The assessment procedure should utilize quantitative measures of stream variables to the maximum extent practicable.
  4. Fluvial Geomorphological Emphasis: Stream assessments undertaken to prioritize watersheds or stream reaches for management or aid the design of stream enhancement or restoration projects should be based on fluvial geomorphic principles.
  5. Data Management: Data from stream assessments should be catalogued by designated entities in each region of the country. This is especially true of reference data.

(Source)