#SchnabelSpotlights: Cooper Lake Dam

Cooper Lake Dam, the primary water supply source for Kingston, New York, underwent a comprehensive rehabilitation led by Schnabel in collaboration with our subconsultant CDM Smith and other Ulster County stakeholders. The project aimed to restore and enhance operability, ensure low-level outlet control, and to bring the dam and reservoir into compliance with updated state Department of Environmental Conservation regulations, all while ensuring high-quality water for the residents of Kingston. The comprehensive rehabilitation design considered spillway capacity, embankment slope stability, and long-term water supply planning elements, contributing to compliance with New York State regulations and future water storage needs.

As part of the design development, we worked with the owner to develop a comprehensive project risk management plan, which included developing a baseline project risk register prior to detailed design work. The objective was to identify, evaluate, assess, prioritize, and plan responses for potential project risks. These included project life-cycle risks spanning from initial permitting and alternatives evaluation, through design development and construction, and, ultimately, to future operations and maintenance.

In support of this approach Schnabel completed a safe yield analysis to assure any work done at the dam considered long term water supply needs. A long-term water volumetric mass safe yield model was developed and calibrated using 80 years of historical Cooper Lake level data allowing users to reliably predict water levels in Cooper Lake. The model was a valuable tool to determine the pool elevation during the construction of the outlet works tower, which required a large coffer dam system. A lowered pool during construction resulted in significant cost and schedule savings. The project team leveraged the safe yield model to assess the potential risks to the water supply system for prolonged construction with a lowered pool elevation. Statistics were developed for the 80-year period of record which analyzed potential pool elevations in relation to historic levels and system constraints highlighting the frequency and severity of droughts. This allowed the City of Kingston to implement a risk-informed decision on a suitable pool elevation during construction that balanced risk to water supply operations with construction cost savings.

The improvements to Cooper Lake Dam, completed under budget, include a new water supply intake tower, outlet works, metering chamber and controls, a spillway and energy dissipation structure and the raising and flattening of the slope of the main dam, and leveling the 1,500-foot west dike.

Notably, the Cooper Lake Dam project is the first in New York state to receive funding for Dam/Reservoir Rehabilitation under the Environmental Protection Agency’s Class Exception, allowing the use of Drinking Water Safe Revolving Funds (DWSRF). The improvements to Cooper Lake Dam will ensure high-quality water supply to Kingston residents for decades to come.

The improvements to Cooper Lake Dam, completed under budget, include a new water supply intake tower, outlet works, metering chamber and controls, a spillway and energy dissipation structure and the raising and flattening of the slope of the main dam, and leveling the 1,500-foot west dike.