Couverden Culvert Removal: Did It Work?
SourDough News | November 19, 2012
Site 1: Culvert before blasting. Photo by Ryan Kreiner.
Site 1: one year post blasting. Photo by Thor Eide.
In 2011, retiree Ryan Kreiner wrote an article on page 14 of SourDough Notes describing the blasting techniques used to remove corrugated metal culverts from a closed logging road at the Couverden log transfer facility near Hoonah. At the time, blasting was the preferred method due to the remote location and extensive vegetation along the existing roadway. The culverts were located in a variety of habitats including three Class I and II fish streams and several Class III and IV streams. The culverts also served as ditch relief for the road. As part of our permit requirements, Matthew Lubejko and I revisited the 14 sites this past August to take stream measurements and photo points, gather botanical data, and sample fish populations.
Taking stream measurements in an area that has been blasted can be a tricky task. When taking bankfull measurements in a natural stream environment, you can tell where the stream would naturally reach a bankfull width. (Bankfull: point from where water begins to overflow onto a floodplain.) However, in the areas where the culverts were removed, this is difficult since the vegetation has not fully regrown. Thus, the measurement we chose to take at each of the sites was the wetted width of the stream, which means the width of the stream at water level. Since we were sampling wetted width, our measurements can vary from year to year based on varying water levels. However, the measurements upstream and downstream of the blasted area can be compared to those in the blasted area on each visit.
To compare the stream in the blasted area to the stream outside of the blasted area, the wetted width measurements were compared. By averaging the measurements taken in the blasted area and comparing them to measurements outside the blasted area, we found a 2.6-inch and 3.2-inch difference between the areas in the non-fish streams in 2012 and 2011, respectively. This means that on average, the stream in the blasted area is 2.6 or 3.2 inches bigger or smaller than the stream outside the blasted area. In the three fish streams we found a difference of 9.1-inch and 8.3-inch difference in 2012 and 2011m respectively. We noticed a larger variability in the fish streams due to the fact that these streams were larger in width and required a larger blast to remove the culverts. But, the question we asked was, do fish use these wider sections of stream?
To sample the three fish streams we used roe-baited Gee minnow traps. A total of 92 Dolly Varden char and 7 coho salmon were captured during our trapping efforts, of which 78 percent of the Dolly Varden and 100 percent of the coho salmon trapped were captured in the blasted areas. The traps that caught the most fish were located near large woody debris that was placed in the stream in the blasted areas to provide habitat.
Photo points were also taken to examine if there was any type of visual change in bank stabilization. By comparing all of the photos, we saw that there has been no change in bank stability. The photo points also allowed us to monitor plant regeneration.
We found that the post-blasting seeding was a success. A combination of annual rye grass and boreal creeping red fescue seeded at all of sites was growing. In addition, native plants were revegetating the blasted area. Botanist Ellen Anderson reviewed our photos to determine which native plants had moved into the area. In our sample site we found goat’s beard, bitter cress, large-leaf avens, yarrow, American brooklime, alder, mosses, devil’s club, willow herb, saxifrage, buttercup, wood rush violets and star flower.
Overall this project has been a great success, the culverts have been removed from a decommissioned road, stream habitat has been restored and enhanced and native vegetation is quickly regenerating the blasted area.
By Thor Eide, Biological Science Technician, Juneau Ranger District and Admiralty National Monument