Reclaiming Reservoirs – Native Species Revegetation of Shorelines

Author: J.L. Jackson, K. Hennebury, D. Baker

This paper summarizes the methodology and results of the first three years of research conducted on the Arrow Reservoir followed by an outline of the program's current status, and recommendations for future monitoring and research. Also included are brief descriptions of other drawdown zone revegetation initiatives recently implemented or proposed by B.C.Hydro based on the Arrow Reservoir model. A final discussion provides insight into the trial and error of reservoir shoreline revegetation efforts and emphasizes some highlights of the research to date.

The Upper Arrow Dust Control Progam provides B.C.Hydro and others with scientific data necessary to the successful planning of shoreline revegetation on hydroelectric reservoirs. We based initial research on limited revegetation studies done in other locations. The actual wetland plant trials required an element of trial and error to determine the effectiveness of propagation techniques and various species over a range of elevation, local climate and substrate conditions. Future revegetation efforts in drawdown zones will benefit from the findings of the Upper Arrow and other B.C. Hydro revegetation programs.One such important finding is that fall rye grain is a hardy, fast growing, and relatively inexpensive nurse crop that does not invade local, native plant communities (inundation in the fall prevents the crop from reaching maturity). Annual fall rye crops provide benefits of soil stabilization, increased organic matter, and stubble useful for nursing native species to establishment in lower elevations within the drawdown zone. The Upper Arrow program had mixed success with fall rye seeding methods. Drill seeding proves most effective for the fall rye as it places the seeds below the hard, dry surface into moist soils where roots can take hold. Aerial and broadcast seeding were least effective because the seeds dried out and couldn’t germinate on the flat, windswept substrate; these methods may better suit inaccessible areas with a more rough, moist substrate (A.E. Brotherston, pers. comm).Secondly, successful revegetation programs require a solid understanding of annual reservoir operations and their effect on shoreline stability. Wave scour, duration and frequency of inundation/drought cycles, and depth of inundation are all operational factors that limit wetland plant survival in the drawdown zone. In the Arrow Reservoir, greenhouse sedge plugs survived a single flood event of up to 7 m of inundation; similar plugs could not tolerate the wave scour of two flood events on Upper Campbell/Buttle Lake Reservoir.

The Upper Arrow Dust Control Progam provides B.C.Hydro and others with scientific data necessary to the successful planning of shoreline revegetation on hydroelectric reservoirs. We based initial research on limited revegetation studies done in other locations. The actual wetland plant trials required an element of trial and error to determine the effectiveness of propagation techniques and various species over a range of elevation, local climate and substrate conditions. Future revegetation efforts in drawdown zones will benefit from the findings of the Upper Arrow and other B.C. Hydro revegetation programs.One such important finding is that fall rye grain is a hardy, fast growing, and relatively inexpensive nurse crop that does not invade local, native plant communities (inundation in the fall prevents the crop from reaching maturity). Annual fall rye crops provide benefits of soil stabilization, increased organic matter, and stubble useful for nursing native species to establishment in lower elevations within the drawdown zone. The Upper Arrow program had mixed success with fall rye seeding methods. Drill seeding proves most effective for the fall rye as it places the seeds below the hard, dry surface into moist soils where roots can take hold. Aerial and broadcast seeding were least effective because the seeds dried out and couldn’t germinate on the flat, windswept substrate; these methods may better suit inaccessible areas with a more rough, moist substrate (A.E. Brotherston, pers. comm).Secondly, successful revegetation programs require a solid understanding of annual reservoir operations and their effect on shoreline stability. Wave scour, duration and frequency of inundation/drought cycles, and depth of inundation are all operational factors that limit wetland plant survival in the drawdown zone. In the Arrow Reservoir, greenhouse sedge plugs survived a single flood event of up to 7 m of inundation; similar plugs could not tolerate the wave scour of two flood events on Upper Campbell/Buttle Lake Reservoir.