Ashokan Reservoir Structures Reconstruction

WSP USA is providing consulting services for improvements to the oldest New York City-owned reservoir in the Catskill Mountains to ensure continued water service.


  • Ulster County, New York, USA


  • New York City Department of Environmental Protection

Ashokan Reservoir at the eastern end of Catskill Park is a critical part of the New York City water supply system, providing approximately 40 percent of the City’s drinking water. Completed early in the twentieth century and placed into service in 1915, the reservoir’s dam and associated structures are over 100 years old.

To ensure an additional 100 years of operation, the New York City Department of Environmental Protection (NYCDEP) is implementing a major improvement project to rehabilitate the reservoir’s various structures, including the Dividing Weir Bridge, Dividing Weir and Ashokan Spillway. The effort is intended to provide adequate hydraulic capacity through the spillways and minimize downstream impacts, while maintaining water quality and vehicular access during construction.

As a major subconsultant, WSP is providing NYCDEP with survey and geospatial activities, planning, hydraulic modeling and analyses for the dam and bridge structures, preliminary through final design, permitting coordination, and bidding and construction support services.

The team will prepare a matrix of proposed design alternatives for various combinations of dam components and transportation elements and evaluate them through hydraulic modeling, considering relative costs, benefits, risks, and mitigation measures. Our hydraulic modeling work includes developing a system-wide two-dimensional model of the reservoir system, and site-specific computational fluid dynamics modeling and physical modeling to evaluate and optimize the hydraulics of the proposed alternatives.