TECHNICAL RELEASE 12-R-4
Roads: wildlife February 2012
Fig. 1: The Problem: "perched" vulvert obstructs fish passage. endangered Atlantic Salmon, fisheries biologists have expressed concern about obstacles to fish passage created by water crossings on logging roads. Bridges, open-bottomed arches, or embedded culverts are preferred methods to maintain or restore natural stream bottoms, facilitating easy passage for spawning fish and smaller juveniles working their way up in headwater streams. A vast system of logging roads has been established over the last fifty years. There are numerous existing culverts installed as water crossings in small headwater streams. One issue biologists are concerned about is perched culverts, in which the outflow end of the culvert extends above the normal water level of the natural stream, creating a waterfall that may present a barrier for fish trying to move upstream. This perched condition problem may be due to inadequate initial installation or because of large rocks or ledge that prevented seating the culverts deeper. A simple method, described here, may enable improved fish passage at a low cost and could extend the life of existing culverts while mitigating the fish passage obstacle they present.GENERAL FEATURES: On a major land holding in the Northeast, the forester planned to open up an old road system for management access. The brush was chipped back, displaced culverts reset and cleaned, and spot-gravelling was done where needed. At the site of a small stream crossing, through a six-foot steel culvert, a perched condition existed—with about a one foot drop from the outflow end. At the same time, the intake end of the culvert was partially plugged by debris washed down during spring floods. The culvert was otherwise in good condition and did not need to be replaced. The road construction contractor used a cutting torch to cut both sides of the bottom of the culvert, curving the cuts in at the end, and then used his excavator’s bucket to push the slot down to the level of the existing stream. This procedure created a “ramp,” creating conditions similar to the natural flow over slanted rocks or a ledge. The configuration should make fish passage much easier, especially for smaller fish. While it may not be the ideal solution, it appears to be a significant interim improvement for a low cost. (Note: This technique may be suitable to improve fish passage in some, but not all existing culvert applications. Consult with fisheries biologists in your area for advice.)
Fig. 2: Possible Solution: modification to culvert improves access for fish.SPECIFICATIONS AND COST: The depth of the cuts in the culvert will vary according to the height of the “perch,” and the length of the overhang, but a good objective would be to cut deep enough so that the resulting ramp slopes less than 45 degrees and reaches the lower water level. Curving the cuts in at the inside end should help to keep the curved shape of the round culvert when it is bent downward, while maintaining some depth of the flow, especially during low summer water levels. The entire job cost the landowner about $200, including work that would have been done anyway. This cost estimate assumes that the equipment had already been brought in for work on the larger road project. It would undoubtedly cost more if the equipment had had to be moved in just for this job.
For more information on fish passage, see Best Management Practices for Forestry: Protecting Maine’s Water Quality (Maine Forest Service, 2010) or your state’s BMPs.
Ted Shina Senior Operations Forester Huber Resources Corporation Old Town, Maine This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Reviewed by: Joel Swanton Northeast Region Manager