Gilboa Dam – Reacting to a Major Hurricane Event during a Major Reconstruction Project

Between Saturday and Sunday, August 27-28, 2011, as Hurricane Irene passed over the eastern-half of New York State, the 314-square-mile watershed for New York City’s Schoharie Reservoir located in the Catskill Mountain Region received an average of 9.2 inches of rainfall. Portions of the watershed received as much as 16.5 inches of rainfall. Storm runoff caused the nearly 2-square-mile-area reservoir to rise by about 20 feet in a six-hour period breaking the previous January 1996 record stage by over one foot. Peak discharge from the reservoir’s impounding structure, Gilboa Dam, has been estimated to be approximately 110,000 cfs; which is more than the typical peak-season flow rate at Niagara Falls.
This flood event, unprecedented for the Gilboa Dam, occurred after four months into a three year major reconstruction project. This paper will discuss the owner’s dam safety program and its emphasis on risk management, provisions in the construction contract for securing the work site for forecast flood events, the timeline of events during the flood, and the initial steps taken to assess the condition of the dam and resume reconstruction work. The lessons learned from this event should prove valuable for other future dam reconstruction projects.