Stream Restoration to Improve Slope Stability along Park Road at Gibsonville, Letchworth State Park, New York

摘要

A road to the historic Gibsonville settlement was originally aligned along the side of a steep valley slope in what would later become Letchworth State Park. Ongoing stream erosion at the toe and soil slope instability along the valley side prompted the park to place a culvert along the stream channel, cover the culvert with up to 20 feet of fill, and realign the road. After almost 40 years, stream hydraulics began causing erosion again, and the culvert showed signs of structural deterioration. Therefore the park determined that the culvert configuration needed to be remediated. A slope stability analysis indicated that excavation for replacing the culvert would require a shoring system to minimize the potential for slope movement. The dense glacial soil present at the site dictated that the shoring system would require drilled soldier piles, which was deemed cost prohibitive. Furthermore, the U.S. Army Corps of Engineers preferred that an ecologically-friendly solution be implemented. The innovative design included abandoning the culvert in-place and restoring the stream to surface flow. Elements of the design included regrading the stream valley to help slope stability, restoring a stream channel that resembled the geomorphic characteristics of nearby reference stream reaches, and building a drop structure that conveys the stream flow non-erosively to the return channel. Construction of the project was completed in 2014.