Canty’s Lake and Silas Condict County Park are popular destinations for fishing, picnicking, and hiking. Canty’s Lake Dam, located in the park, is a Class II – Significant Hazard dam that required major rehabilitation.
The dam’s most critical deficiency was the significantly undersized existing spillway. The small spillway and lack of freeboard was not capable of passing storm events as small as the 1-year storm event without overtopping the dam. In addition, there was no working low-level outlet or other means to lower the lake as required by the Bureau of Dam Safety (Bureau). The Bureau ordered the Morris County Park Commission (MCPC) to rehabilitate the dam to pass the required Spillway Design Storm (SDS), which is the 0.5 Probable Maximum Precipitation (0.5 PMP).
GZA worked closely with the MCPC and the Bureau to conduct hydrologic and hydraulic modeling and stability analyses and developed a practical design that also created public access around the entire lake. The rehabilitation design included a combined primary/auxiliary box culvert spillway structure and a raised crest to provide one foot of freeboard during the 0.5 PMP. A new 10-inch diameter PVC siphon system was designed to satisfy the requirement for a low-level outlet.
GZA’s pragmatic solution achieved compliance with the New Jersey Dam Safety Standards and significantly enhanced the recreational opportunities at the park.