Approx. $1.8 million
As early as 2006, approximately 600 linear feet of streambank along the West Branch of the Delaware River, in the Village of Walton, NY, was observed to be actively failing, posing a significant risk to public infrastructure and private property.
Property owners near the intersection of South Street and Stockton Avenue have observed the loss of between 10 and 20 feet of private property along the West Branch due to constant erosion across the past 25 years, a process that has been dramatically accelerated during high-flow events like the floods of 1996, 2006, and 2011. The introduction of these additional sediments was threatening water quality within a key drinking-water reservoir for New York City, while the ongoing erosion threatened not only private property, but also access to important community facilities like the Delaware County Fairgrounds, the Village’s wastewater treatment plant, an industrial park and National Guard facility. Lastly, municipal utilities – like sanitary sewer, water distribution piping, storm-drain infrastructure – were located within the affected streets, and overhead electrical and communication infrastructure was in place at the top of the failing slope on South Street.
Delaware Engineering, working with Shumaker Engineering, the Delaware County Soil & Water Conservation District (DCSWCD) and the New York City Dept. of Environmental Protection (NYCDEP), performed field observation, subsurface investigation and hydrologic analysis in order to address the hydraulic and geotechnical causes of bank failure. Delaware developed several engineering alternatives designed to stabilize the compromised streambank, to protect municipal and private property and infrastructure, and to ensure drinking-water quality.
Engineering and field analysis concluded that the streambank was being undermined, in large part due to the high plasticity of the streambank’s soil, glacial till gravel that gradiates to silt and clay. As a result, the streambank toe was eroding during high discharges, causing streambank failure. Ultimately, DCSWCD, NYCDEP and the rest of the project team concluded that subsurface anchoring of metal sheet piling along the existing streambank would be the most advantageous methodology to address streambank erosion cost-effectively, while avoiding placing additional fill within the channel.
Design was completed in 2018, and construction completed in 2019 at a cost of approximately $1.8 million. Delaware assisted DCSWCD in securing grant funds from the Army Corps of Engineers, NYS Department of Environmental Conservation and NYCDEP totalling almost $1.5 million. The project compliments the soil reclamation project taking place directly across the river on Water Street, and together these projects promise to slow floodwaters and to bolster the Village’s flood mitigation capacity.