By Kathy Savolt -
At the March 27 Board of Trustees meeting, a representative from GHD, a self-described global network of multi-disciplinary professionals providing clients with integrated solutions through engineering, environmental, design and construction expertise, presented the draft findings of their analysis of the Mamaroneck Reservoir Dam. The dam, officially classified as a High Hazard dam, was found to be structurally sound but it does not have sufficient spillway capacity.
After New York State issued new regulations for dam safety in 2012 the dam became non-compliant. After the third notice of violation was issued in April 2022, Village Manager Jerry Barberio declared a local emergency that led to the GHD study. See HERE .
These findings were no surprise to some long-time Village residents. In 1981, the US Army Corps of Engineers also studied the dam and declared it unsafe for the same reason. See HERE.
Four Alternatives
Ken Catino, the GHD representative, presented four alternatives for bringing the dam into compliance. See HERE.
Alternative 1 is to apply for a variance from the regulations. Catino explained that some rehabilitation would probably still have to be done but this was the most cost-effective solution with a rough estimated cost of $1 million.
Alternative 2 is to increase the spillway length. This would require the construction of an auxiliary or overflow spillway. This alternative would require easements from adjoining private property owners and was estimated at $3 million.
Alternative 3 is to reconfigure the spillway. This would require the construction of a new dam immediately downstream from the existing dam with a design that would increase the spillway capacity to comply with the current regulations. This alternative was the most costly with a rough estimate of $4 million.
Alternative 4 is to remove the dam and allow the Mamaroneck River to be restored to its original state. This would cost about $3 million.
Catino reported that the next steps were to finalize the report for the Village and submit it to the NYSDEC. This starts a timetable for the owners of the dam to remediate the problem.
Who is Responsible?
The dam is owned by the Westchester Joint Water Works, not the Village of Mamaroneck. According to Mayor Tom Murphy, a 1977 Maintenance Agreement between the Village and the Water Works required the Village to commission this study and consider the alternatives. See HERE.
As pointed out by resident Doreen Roney later in the meeting, the Village work required under the maintenance agreement is limited to a 24” valve, the pipeline and intake structure to said valve, twin conduits and screens, and the access way to the interior of the dam (see pages 2-3 of contract). This is the only work the Village of Mamaroneck is responsible for. Roney asked why the Village wants to take responsibility for repair or replacement of the dam outside the scope of the maintenance contract. This question remains unanswered.
Impact on Flooding?
Several residents questioned the dam’s ability to control flooding. Trustee Lou Young asked if the reservoir were widened and deepened, would that impact the storage capacity of the reservoir? He continued that if a new dam were constructed, could they empty the reservoir prior to a storm to increase its holding capacity? Catino said increasing the dam’s ability to control flooding was not a part of this study. A new dam could provide flood protection, but the hydrology and hydraulics would need to be thoroughly analyzed. Long-time residents recalled the days when the reservoir overflowed onto Mamaroneck Avenue, cutting residents off from both north and south.
The Village has included the dam and reservoir as part of what they call parallel flood control: local actions to be taken in addition to the Army Corps of Engineers project.
The Mamaroneck Observer will continue to report on this story as it unfolds.
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