Instream Debris Removal
Photo 1: Woody debris causing complete obstruction to fish migration.
Photo 2: Ensure stream is not obstructed. Woody debris across the stream width may cause future damming.
The removal of instream debris is a commonly used stream improvement technique. Generally it is applicable in areas where large amounts of man made refuse result in the formation of obstructions to fish passage caused by jams of woody debris, organic material and/or fine sediment. Buildup of debris can also cause adverse impacts such as scouring of existing spawning gravels or the erosion of streambanks.
Removal of instream debris should be conducted according to the following guidelines:
- DFO should be contacted prior to initiating any debris removal project. Acceptance of a project by the Department does not release the applicant from any obligation to obtain permission from or to comply with the requirements of any other regulatory agency (e.g., federal, provincial or municipal).
- Remove all man-made debris in order to achieve a natural stream environment.
- Woody debris that provides shelter/cover for fish, or contributes to the diversity of habitat features within a stream (e.g., pool scouring), should be left in place.
- Trees which have fallen across a stream should be trimmed or removed if they result in damming or creation of a stream diversion, which can increase downstream erosion and sedimentation.
- Only remove woody debris that forms a complete obstruction to fish movement.
- Restrict activities to a relatively short stream reach (100 m) at any one time. Commence activities from the downstream end working in an upstream direction.
- In general, debris removal should begin in the center of the stream and progress towards the banks.
- If large amounts of sediment are likely to be released, conduct work during the lowest flow period in the summer and limit instream activities. Other mitigations may be required as specified in government permits or advice (e.g. siltation control measures).
- Project timing is important and is usually specified by regulatory agencies. Instream work should not be conducted during the spawning or egg incubation period.
- The use of heavy equipment near a stream should not be utilized unless necessary. If it is required, banks should be stabilized and appropriate government guidelines followed. The operation of machinery may necessitate revegetation and restabilization upon project completion.
- In some instances it may be possible to simply reposition some debris to maintain habitat diversity and encourage scouring flows.
- When restoring small, smothered streams, remove only enough material to expose some bottom substrate. This should only occur in rare circumstances under the supervision of a biologist. In order to be effective, the technique should be combined with a velocity increasing technique (e.g. wing deflectors) to keep some areas of the bottom substrate scoured clean. It may be desirable to remove silt from the streambed using appropriate mitigation techniques in order to prevent siltation further downstream.
- Trees, bushes, shrubs, weeds or tall grasses should not be removed along a bank unless the vegetation is choking the small stream (e.g., urban streams). In such instances thinning or selective removal may be appropriate. Mats of floating algae or vegetation should not be removed from any section of a stream.
- All debris removed from the stream should be disposed of to ensure that it does not re-enter the watercourse.
Monitoring and maintenance
The stream should be monitored periodically to remove debris and any other obstructions that may develop. Check streambanks to ensure their stability is maintained and revegetation has been successful. Continue smaller scale debris removal efforts if required.
What You Need To Do
If you are going to do a project in or around water, there are three steps that you should consider following to avoid impacts to fish and fish habitat.
Buchanan, R.A., D.A. Scruton and T.C. Anderson. 1989. A Technical Manual for Small Stream Improvement and Enhancement in Newfoundland and Labrador.
Scruton, D.A., T.C. Anderson, C.E. Bourgeois and J.P. O’Brien. 1992. Small Stream Surveys for Public Sponsored Habitat Improvement and Enhancement Projects.
For more information contact the nearest
Department of Fisheries and Oceans office.