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Nova Scotia Power to construct new Tusket hydro dam in Yarmouth County and demolish the old one


YARMOUTH COUNTY, N.S. – A major project ­– both in cost and scope – will be carried out by Nova Scotia Power over the next two years in Yarmouth County involving the construction of a new hydro dam followed up by the demolition of the existing one.

Nova Scotia Power is embarking on a Tusket Main Dam Refurbishment Project with the work slated to start in July, providing all permits and requirements have been met. Approvals are required from the Utility and Review Board and the departments of environment and fisheries, as some examples.

The new dam structure will be built in front of the existing one. Nova Scotia Power says it won’t be changing the Lake Vaughan water elevations during or after the project.

“We’ll come in and build for about six months in the river bed. We’ll leave at the end of November, go away for six months so that we have time for the gaspereau fishing season to occur and once that ends we’ll come back again and build for another six months,” project manager Browren Allard explained during a packed open house at the Lake Vaughan fire hall on April 11. “So we’re looking at a construction time of about 12 months, but it’ll take place over the course of two years.”

She said the estimated cost of the project is between $10 and $15 million.

The existing bridge near the Tusket dam may need to be replaced.

Aside from replacing the dam, there is a possibility the adjacent bridge will be replaced too.

“We’ve been working with the department of transportation because it is their structure. If we do end up having to replace the bridge, the bridge will go in new, exactly where it is right now, so the alignment will stay the same,” Allard said. She said a pre-fabricated bridge could be used first as a temporary structure and then as a permanent replacement structure. She noted during the process there could be a week without any bridge access.

George Emin, chief of the Lake Vaughan Fire Department, asked about weight restrictions since the bridge is used heavily by the fire department. Allard said there wouldn’t be any change from what already exists.

A new dam structure is needed to meet Canadian guidelines that were updated in 2007. Allard said since 2008 Nova Scotia Power has been addressing dam structures throughout the province to bring them in line with the guidelines. There are 178 structures across the province, she said, explaining they started with the high-risk structures first.

This Yarmouth County project, Allard said, has been one of the more complicated projects to prepare for, design and execute.

The project is a big undertaking.

ABOUT THE WORK

The gates of the existing dam are nearing the end of their expected life, with major concrete deterioration occurring. There is also significant water leakage, causing ice build-up in the winter. The existing dam has four gates that use pivot points to open and close. The new dam will have eight lift gates that lower and rise. If all of the gates are open, the new dam will be able to pass 28,800 cubic feet of water per second through it, compared to 20,000 with the existing dam.

No changes are planned to the Nova Scotia Powerhouse as part of this project, it will generate power as normal.

Allard said a goal of the new structure is to pass water during a significant flood situation and to ensure very specific flood management. The last major flood in the area was in November 2010.

FISH LADDER CONCERNS

Aside from questions about the work itself, those who attended the open house were concerned over potential impacts to the dam’s fish ladder.

“The fish ladder will stay in place, it works fantastic, we don’t want to mess with it,” Allard said. “The plan is right now that it will be fully utilized during the first year of construction. During the second year of construction we will have to de-water it for a period of time to be able to keep that whole area dry for concrete construction as well as we do have to raise the sidewalls of it to match the new ground elevation.”

Still, people were seeking reassurances. George Emin asked if there is a backup plan if the fish ladder fails completely after the new dam is built.

Nova Scotia Power said it is working with the department of fisheries regarding the fish ladder and that it will be monitored and evaluated during and after construction. Nova Scotia Power said it isn’t anticipating any impact, but it is taking the concerns raised to heart.

Emin said if there is a problem with the fish ladder it will need to be addressed ASAP.

“You need an emergency plan immediately,” he said. “Not the following year.”

 

FYI:

The Tusket Hydro System has been in operation since 1929 and consists of one hydroelectric generating station with a capacity of 2.7 megawatts and four storage reservoirs at Lake Vaughan, Raynards Lake, Mink Lake and Great Barren Lake. The station generates about 12,000 megawatt-hours of electricity per year, which is enough to supply 1,200 average homes. The hydro system has a drainage area of 1,458 square kilometres, the largest drainage area of Nova Scotia Power¹s hydroelectric systems.

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