Representatives of a citizens watchdog group called Friday for more details about the reasons behind New York City’s decision that the planned rehabilitation of the Gilboa Dam would take at least a year longer than expected.
“It was pretty evident to us that there was pretty compromised bedrock,” Dam Concerned Citizens spokeswoman Gail Shaffer told the county Board of Supervisors.
A city spokesman contended later that rock supporting the dam is safe and in good condition.
Shaffer, a Blenheim resident and a former state secretary of state, noted that a revised schedule announced Jan. 11 by the New York City Department of Environmental Protection raised the estimated project cost from about $315 million to $583 million.
“That shows that something significant needs revision,” Shaffer said.
No city officials attended Friday’s meeting, but asked about the Shaffer’s concern, NYCDEP spokesman Michael Saucier said “the issue is not the condition of the bedrock — it’s the depth of bedrock.”
Rock in the area under consideration for a tunnel under the dam apparently is too deep, according to city officials.
“We are confident that the condition of the bedrock directly underneath and supporting the dam is completely safe and completely competent rock,” Saucier said.
“We are performing boring work to locate a suitable location for the intake and tunnel for the low level outlet … and thus far, upstream of the dam, in the reservoir, we haven’t been able to locate rock at a proper depth,” he said.
Those investigations and borings are expected to continue in the spring.
In revising the reconstruction schedule, DEP Deputy Commissioner Paul Rush told county officials last week that the changes were largely “due to continued site challenges related to developing the final design for the low-level [water] release works at the dam.”
“They’ve been having difficulty finding a site for that low-level release,” county board Chairman Earl Van Wormer III told Shaffer Friday.
In October, Rush predicted the overall project might take longer than expected because of problems finding a suitable location to build a 14-foot-diameter outlet that would for the first time let water downstream into the Schoharie Creek from the Schoharie Reservoir.
The massive rebuilding of the 80-year-old, 182-foot high dam is now planned as a five-phased project beginning at the end of this year and ending in 2014.
Shaffer and Dam Concerned Citizens Secretary Sherrie Bartholomew called for closer involvement by county engineering experts to participant in the project planning.
Van Wormer said the county’s consulting engineer Mike Quinn has been talking with Rush regularly.
City officials have expressed confidence that a $24 million interim reinforcement project completed in December 2006 significantly strengthened the dam after city engineers raised concerns that it might fail if water levels exceeded the record January 1996 flood that devastated Schoharie Valley communities below it.
As a result of the stabilization, city officials confirmed Friday that the dam would hold in a “probable maximum flood” that brought water 17.8 feet over the dam.
Before the stabilization work anchored the dam to bedrock with a series of steel cables, that mathematical safety level was only 8 feet above the dam.
Bartholomew also urged Friday that a “protocol for operation of the [proposed] gates [atop the dam] as flood control,” should be agreed upon first.
As currently planned, an $8 million system of crest gates will be installed in 2009 in a notch that was cut 51⁄2 feet down from the top of the dam to release water before the six-mile-long reservoir began overflowing.
Incorporating flood-control elements into the dam is a departure from the history of the 19-billion-gallon reservoir, which was built to supply water to the city.
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Categories: Schenectady County