Hackettstown Reservoir Dam Interim Lowering

The Hackettstown Reservoir Dam is a Class I – High Hazard Dam located on the Mine Brook, a tributary to the Musconetcong River. Princeton Hydro has been working on this dam since 2006, when it was owned by the Hackettstown Municipal Utilities Authority. This 42-foot high dam, that impounded an 8-acre lake is a cast-in-place concrete gravity dam constructed in the early 1930s to supply potable water to the residents of the Town of Hackettstown. It was constructed as an initiative of the Work Projects Administration (WPA). The dam and property within which the impoundment is located, was purchased by Ironbound Mt. Olive Holdings, LLC about 8 years ago, who is the current owner.

Princeton Hydro completed a stability analysis, a dam breach and spillway design storm analysis, and inundation mapping, and have been performing inspections on a bi-annual basis, when requested. As a result of the hydrologic and hydraulic analysis, the dam was reclassified from a Class III, Low Hazard to a Class I, High Hazard Dam. As the dam does not meet the Dam Safety standards for overturning (stability) and it cannot safety pass the spillway design storm, NJDEP Dam Safety order the dam to be upgraded or decommissioned.

In 2022, an application for an interim lowering was prepared and submitted to NJDEP Dam Safety. As part of the application, Princeton Hydro completed calculations to assess if the impoundment was completely emptied and the valves remained fully open would it still create a potential hazard in the event of a storm event. While it was concluded that during the SDS the dam may still overtop, the duration of overtopping was significantly reduced, and the impoundment would empty again in a matter of a few days. Dam Safety agreed with this approach, and Princeton Hydro designed the lowering and monitoring plans, oversaw the installation of backup valves in the event the original valves failed to close, if found necessary, and provided updates to Dam Safety on the project.

The dam currently remains completely dewatered while plans are prepared for its ultimate decommissioning, expected to be completed in 2024.