Innovative engineering preserves popular recreation site
October 27, 2006
Each year primarily during the summer months, hundreds of visitors, nature enthusiasts, recreation seekers, and local residents visit Vermont's 850-acre Waterbury Reservoir campsite. They make the journey to enjoy the outdoor activities available along the 19 miles of pristine shoreline. They find the popular area perfect for camping, fishing, hiking, and water sports.
However, during recent years, the sloped banks along the shoreline had become unstable due to erosion. In response, the Corps used traditional and innovative engineering techniques to stabilize the reservoir banks.
The erosion is due to a number of factors, including the drawdown of the reservoir performed every winter when the campground closes, and wave action from recreational boats on previously exposed shoreline.
In 2000 Vermont lowered the reservoir due to safety concerns at the nearby Waterbury Dam, and lowered it again in 2002 when the U.S. Army Corps of Engineers began construction work on the dam. In recent years, the dam has experienced seepage problems and New York District, with help from other Corps districts, has made repairs that are expected to be completed this fall.
The reservoir is normally at summer pool level, 590 feet. To perform these repairs the reservoir was lowered in 2002 to 520 feet. Presently, the water is at 550 feet and will be back to summer pool level when the work is completed.
Lowering the reservoir takes pressure off of the dam, reduces dam seepage, and allows safer construction work, but there is a price. The reservoir's annual lowering, plus the additional lowerings in 2000 and 2002 contributed to shore erosion.
The sloped banks of the reservoir are vegetated. When the reservoir was lowered, it exposed lower portions of the bank that are not vegetated. This exposed bank eroded and uprooted vegetation, especially during rainfall. Losing the vegetation left upper portions of the bank exposed and subject to erosion.
Bank erosion causes big problems in man-made lakes. When the ground is exposed, it's easy for groundwater to percolate out of the soil and contribute to the slope's erosion and adding even more soil to the reservoir.
If this runoff continues, the campground can lose large portions of land, and the flow of sediment into the reservoir muddies the water, reduces its oxygen level, and increases the water temperature, all of which harms water habitats.
This summer, the Corps and the state of Vermont built a shoreline stabilization project for 1,100 feet of reservoir shoreline using both traditional and bioengineering methods.
"Traditional techniques are being used to stabilize the bottom of the slope," said Marty Goff, project engineer from New York District. "This includes using stone, or riprap, on the toe, or the bottom, of the slope. The weight of the stone prevents wave action from moving or removing the stone, and prevents scoring or erosion of the toe of the slope. This part of the slope must remain stable for the upper reaches, which were stabilized using bioengineering techniques, to remain in place and function properly."
Bioengineering techniques are a variety of methods that use dormant plant cuttings from woody plants to alleviate soil erosion. The plants are planted in specific arrangements in the soil depending upon the technique. The cuttings come from plants that root easily, and the root system holds the soil together to prevent sediment loss.
Only native plants are used. The toe, or bottom, of the slope will be planted with willow, dogwood, and alder to provide quick rooting. The remaining slope will be planted with a mix of low-growing to medium-sized shrubs such as bearberry, snowberry, sweet fern, and lowbush blueberry.
Trees include gray birch and gray dogwood. Along the top of the slope the white pine and eastern hemlock are being planted to blend in with the camping area.
"Vermont has been a strong proponent of bioengineering, and they encouraged us to use it in this project," said Goff. "The Corps has used bioengineering in the past, but just using grass. This is the first time we used native plants. This is a departure from the more traditional approach, which typically involves steel sheet pile and back-filling. The result is a more natural and sustainable slope."
Combining both traditional and bioengineering techniques is beneficial because a stable slope is achieved without diminishing the natural appearance. The project will not have the "engineered" look of many slope stabilization projects.
The environment also benefits from combining techniques. Planting vegetation along the shoreline provides nesting and foraging habitats for native birds, and it maintains the look and feel of the region.
Presently, the toe stabilization at the bottom of the slopes is complete. Grass seed is now being placed on the tops of the slopes for immediate slope stabilization. This fall, a mix of live cuttings and containers of woody vegetation, such as shrubs and trees, will be planted on the slopes for longer stabilization.
Planting in the fall is more conductive to plant survival than planting during the summer. The campground will be closed for the winter. When it reopens next spring, the restored portions of the shoreline will be open to the public.
Goff provides the following suggestions for other engineers performing similar shore stabilization projects:
* Coordinate constantly with your various state agencies to make sure everyone agrees with the schedule and project goals.
* Consider the "green" approach when trying to stabilize slopes. This bioengineered slope should be as stable as a typically constructed "hard" design.
"A significant thing we've learned from this project is that it's important to always be open to new and innovative ideas, even if they deviate from the traditional," said Goff.