Report: Windsor Dam Safety Below Standard
On Nov. 14, 2011, Will Hayes, of Daniels Construction, carries lumber to the base of Ascutney Mill Dam in Windsor, Vt., as part of a project to stabilize the 177-year-old structure. (Valley News - Jennifer Hauck) Purchase photo reprints »
Windsor — A consulting engineer hired to analyze the Ascutney Mill Dam that forms Kennedy Pond said that the dam’s overall stability and spillway capacity are both below safety standards and higher spillway flows raise the risk on the buttress shell.
The analysis was presented at the Selectboard Tuesday night as part of a report on the condition of the dam and options for repairs.
“We are looking at the ability of the dam to pass floods based on the design criteria of a 44 square mile drainage (watershed) basin,” said Phil Moreschi of Manchester, Conn.-based Fuss & O’Neill, explaining the goal of their analysis and recommendations.
Moreschi and Mike Taylor of Geo Design in Middlebury, Conn., and Windsor and said they expect to finalize their recommendations to present to the Selectboard in November.
Toward the end of Tuesday night’s presentation, Town Manager Tom Marsh said the town should have cost estimates for the repair options about the beginning of the year and can then decide on a bond amount for voters to consider at Town Meeting in March.
In the spring, a cofferdam was constructed and a large amount of silt was removed to allow the installation of a new sluice gate on the roughly 180-year-old dam.
Water can now flow from the bottom, reducing the pressure on the spillway.
Geo Design and Fuss & O’Neill were hired in June to conduct a hydrologic and structural analysis of the dam.
Some the options in the report included reconstructing the spillways and related masonry, repairing the concrete face and rebuilding the buttress shell, the stone portion at the base of the dam.
Engineers presented slides during the presentation that showed the condition of the dam, including the severe cracks in the concrete on the upstream side.
Also in the report were some preliminary alternatives to reducing the flow at the 300-foot spillway, or the top of the dam.
Lengthening the spillway 80 feet to the west and building a concrete spillway channel, lowering the level of Kennedy Pond or raising the height of the spillway were presented for consideration.
Taylor and Moreschi referred to “factors of safety” of the dam and designing the repairs to make it resistant to high flows as would be experienced in a 100-year flood.
The report gives the dam a fair or poor rating for different conditions including high spillway discharge.
“The buttress shell has a low safety factor,” Taylor said.
While removing the dam was mentioned, it was not among the alternatives presented and would likely not be considered because Kennedy Pond is a popular recreation area for the town.
Patrick O’Grady can be reached at firstname.lastname@example.org.