Evaluate historical behavior of a stream

By; R P(Bob) Willington, Ph.D., R.P.F., P,Geo.

An excerpt from an article entitled "Stream Controll for Forest Roads" which appeared in "Drainage Structures for Logging Roads" April, 1979, Sponsored by; the Association of British Columbia Professional Foresters and the center for continuing Education, The University of British Columbia.

Examining the past spatial variation of the creek frequently reveals some clues as to the future variation that might be expected over the design life of the road and/or crossing structure. This examination should include the entire stream reach, the upstream reach and the downstream reach rather than just the area within which construction is planned.

The behavior of the stream at any point is dependent on the character of the stream at that point plus the upstream and downstream environments.

The examination process should minimally include the following: Examine old air photos for differences in spatial behavior. Experience has shown that some portions of a stream reach are more stable than others suggesting potentially preferable crossing locations. Further, historical air photos may suggest river control points (eg bedrock, lateral tributary effect) not easily discernible on recent air photos or by ground checks.

Experience has shown that a helicopter recce for the project area yields valuable input of data to the design. For larger streams, photos taken during the recce can be used to develop an overlay of the stream to compare present location with historical locations.

Ground checking augments that which has been deduced from the air photos. On large streams, ground checks are of minimal value in predicting stream changes due to visible scale limitations. On small streams, ground checks are critical owing to the lack of detail visibility on air photos or aerial recce.

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