The Findley Lake Dam is an earthen embankment located at the northern end of Findley Lake in the Town of Mina, New York. It is owned and operated by the Findley Lake Watershed Foundation (FLWF). The dam is approximately 160 feet in length and 10 feet high with a volume of about 3,600 acre-feet at the normal pool. The dam was built in the early 1800’s and has undergone several modifications since construction. In the late 1990’s the NYSDOT installed a new precast concrete inlet box, a new slide gate at the inlet, lined the existing concrete box culvert with a new corrugated metal pipe, and placed flowable fill backfill in the annular space between the existing box culvert and new pipe.

In 2012, FLWF representatives noticed a leak at the seal between the corrugated metal pipe and the new inlet box structure. Sink holes developed in the pavement above the inlet structure in the months after the leak was first observed.

McMahon & Mann was engaged to explore the conditions at the dam and the causes of the leak and sinkholes. Following the completion of test pits at the inlet structure and a dam safety inspection, we concluded that water from Findley Lake was flowing below the dam’s upstream wall and into the inlet structure though a void in the seal between the corrugated metal pipe and the inlet box structure.

We designed remediation measures to stabilize the upstream wall and reduce the seepage through the embankment. The design included a sheet pile wall driven a few feet upstream of the concrete wall. The space between the walls will be backfilled with controlled low strength material to support the existing wall and create a seal to limit infiltration through the dam.

We observed construction activities including sheet pile wall installation, CLSM placement and placement of the upstream riprap. Construction was completed in 2017.