Gannett Fleming wins conservation engineering awards

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HARRISBURG, PA. — Gannett Fleming, an international planning, design, and construction management firm, was honored in the Association of Conservation Engineers’ (ACE) 17th annual Carl Anderson Conservation Project Engineering Awards. The Valley Forge Park Water Main and Stream Restoration Project in Chester County, Pa., received the Award of Excellence, and the Conowingo Dam Fishing Enhancements Project in Darlington, Md., received the Award of Merit.

Awarded annually, the Carl Anderson Conservation Project Engineering Awards recognize ACE members for outstanding projects in conservation engineering. The purpose of the competition is to recognize members whose work, as judged by their peers and associates, best exhibits the goals and objectives of ACE. Both projects were submitted in the conservation/environmental category.

Valley Forge Park Water Main and Stream Restoration Project
Valley Forge National Historical Park in Chester County, Pa., annually hosts more than 1.4 million visitors. A 36-inch high-pressure water transmission runs through this vast 3,500-acre park, providing water to more than 150,000 people in Chester County. A section of this main, where it crosses Thropp’s Creek, had been subjected to years of erosion, resulting in a significant portion requiring immediate restoration.

To remediate the main and restore the stream, Gannett Fleming incorporated a series of six step pools constructed of imbricated stone to create a series of overflowing pools. The stream bed upstream of the first pool, which covers the water main, was also raised and flattened to reduce the slope of the stream and result in a slower, less erosive stream flow. Each pool is approximately 25 feet in length, and the total reconstructed stream bed encompasses approximately 400 feet in overall length. The stones are keyed into the banks on either side to stabilize and prevent scouring around the edges.

Coir logs, fascines, and live stakes were installed on both stream banks. The areas above the coir logs and fascines were covered with erosion control matting and planted with native trees and shrubs for further stabilization. The engineering design maintained the character of the park and stabilized the eroded creek channel to prevent a recurrence of the problem and comply with National Environmental Policy Act requirements.

Conowingo Dam Fishing Enhancements Project
The Conowingo Dam, located on the Susquehanna River in Darlington, Md., offers exceptional recreational opportunities to the public, including fishing, bird watching, hiking, boating, and camping. For security measures, public access to the dam has been restricted in recent years. This project was undertaken to mitigate the lost recreational opportunities and to provide enhanced access for people with disabilities to enjoy the natural resources at the dam. The project included constructing a new scenic walking trail along the east bank of the river and a new fishing wharf on the west bank.

Through numerous public meetings and interactions with local fishing groups and citizens, a very creative and state-of-the-art shoreline fishing wharf was designed. The new wharf consists of terracing the riverbank with a series of ramps and steps that provide new and safer fishing opportunities where access was once hazardous. The post and lagging wall design enabled construction in the wet to address the daily fluctuation of unpredictable river levels created by hydropower operations. Handicap-accessible textured concrete ramps were designed to provide a functional and aesthetically pleasing structure. Embedded submersible lights provide nighttime access and use of the wharf. Seating, resting, and educational opportunities were also incorporated into the design. The large terraced steps leading to the river provide fishermen greater use of the site for a wider range of river flow conditions.

The fishing wharf and walking trail were completed within the constraints of an accelerated design, permitting, and construction schedule. Construction within the river was complicated by the daily operation of the Conowingo Dam hydroelectric power plant, which resulted in highly variable and unpredictable flow conditions. The site also had a limited staging area, and in-stream work restrictions were imposed to avoid impacts to fish migration, including a zero-tolerance policy for releases into the Susquehanna River.