Fish passage would require shutdowns of Annapolis tidal station, NS Power tells regulators

Nova Scotia Power provided more evidence this week to justify its decision to permanently retire the Annapolis tidal power generating station, claiming federal fish passage requirements would shut down the facility for several months each year.

NSP has applied to the Nova Scotia Utility and Review Board to write off the 37-year-old generating station and charge ratepayers $27 million over the next decade to recover the remaining value of the asset.

The station, which produced enough electricity to power 4,500 homes, stopped operations in 2019 after a generator failure and an order issued that same year from the Department of Fisheries and Oceans.

DFO ruled the turbine blades were killing fish in the Annapolis River and the plant would require authorization under the Fisheries Act to operate in the future.

"The geography and configuration of the Annapolis Tidal Plant area make it challenging to develop and maintain effective fish guidance systems to deter fish from entering the turbine," NSP told the utility and review board this week.

"Therefore, based on NS Power's experience, under a DFO authorization, the potential operational modifications were understood to be a complete shutdown period (i.e. full month) to allow for fish migration of critical species."

4 months of shutdowns

The company modelled the amount of time the plant would be shut down to accommodate fish passage, but the information was filed confidentially.

In response to questions from the regulator, it did provide a table showing fish migration periods that were used as the basis for its estimates.

The chart showed gaspereau and shad migration occurs over four months from April to July. Migration of American eel was listed from August to December, and tomcod in January and February.

NSP released a range of shutdown probability, and found four months each year was most likely.

DFO said it only indicated that authorization was required.

"As part of a Fisheries Act authorization application, it is the responsibility of the proponent to develop and present ways the project could avoid, mitigate or offset impacts to fish and fish habitat," DFO told CBC News.

It also said Nova Scotia Power has not applied for Fisheries Act authorization for the facility.

The power company would not comment.

Retiring station 'extremely significant'

NSP will now submit a separate application for approval to decommission North America's first tidal generating station.

"I think it's extremely significant. This is something that's had a fairly profound impact on the Annapolis River, on fish populations, on the land upstream of the tidal generating station," said Levi Cliche, executive director of the Clean Annapolis River Project, a conservation group in the area.

"We have a lot to think about in terms of how we move forward. We really need to consider how this infrastructure operates and how it's altered for the benefit of the ecology and landowners going forward."

The seven-metre, 148-tonne turbine is located in a causeway across the Annapolis River built in the 1960s to protect farmland upriver from being flooded by the Bay of Fundy tides.

Environmental assessment needed

The causeway reduced tidal movement upstream, leading to low oxygen conditions and nutrient buildup, said Cliche.

The tidal power generating station provided increased flushing, better mixing and some localized ecological improvements.

Cliche said removing the causeway would fully restore tidal flows but increase erosion and risk overtopping dikes that have not been maintained in decades, threatening existing farmland and private properties.

"It's complicated," he said.

For fish in the Annapolis River system, removal of the spinning blades is a good thing.

"The tidal generating station has caused mortality of several different species over a number of years and has impacted population, though the extent of which isn't really fully understood. But it can only be a benefit to species recovery," said Cliche.

Decommissioning the station will require an environmental assessment. In previous filings, NSP has estimated the cost at over $200 million.

The utility is obligated to return the causeway to the province in the state it found it.

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