Gowanda Bypass and Dam Safety Project

Abstract Only - The Gowanda Reservoir and dam in southwestern New York State is comprised of a 250-foot-long, 22-foot-high embankment dam used for the village water supply. The dam is located in a very narrow valley of Point Peter Brook just before it outlets into Cattaraugus Creek which is a tributary to Lake Erie.
The area in which the dam resides is prone to very quick time of concentrations resulting in heavy flash flooding on a regular basis. The last event in 2011 resulted in the dam being overtopped, the control house being inundated and the loss of a roadway leading to the dam. It was estimated that the event was approximately a 1% chance event.
During early design, it was determined that due to the dam geometry, resizing of the existing spillway would be cost prohibitive and would disrupt the water supply for the village.
Currently the reservoir is not being fed by Point Peter Brook or its associated basin under normal flow conditions. Under normal conditions, the reservoir is completely fed by a spring tied to the local aquifer. During the 1960’s, Point Peter Brook was re-routed under the reservoir using 5 foot conduit CMP that would channel normal flow around the reservoir. However, the pipe is not able to handle a large storm event such as the event in 2011.
To mediate this, a project is underway to replace the existing pipe with a larger combination precast and cast in place culvert along the same alignment that will convey the 100-year storm around the reservoir without affecting the capacity of the reservoir or overtopping the dam. The difficulties of this design include routing a large culvert through a narrow valley that is shared by the reservoir, “punching” the new culvert through the existing core wall of the dam and not increasing the chances of seepage or piping through the core wall. Measures taken to provide a safe dam include special structural details of the culvert and its penetration through the core wall, waterstops at culvert joints and at the intersection of the core wall, special bedding of the precast and cast in place culvert, and filters used within the embankment.
Work included Dam Safety coordination with local governments, State Dam Safety and FEMA whose grant funded the project. The resulting design will allow for a cost effective way for the system to safely pass a NYSDEC Class A design storm of 100-years without major reconstruction of the dam or waterworks.