The greatest threat to the Fortress of Louisbourg was once invasion by the English, but nowadays the former military site in Cape Breton must defend itself against the forces of nature.

Climate change and sea-level rise could cause flooding, which has prompted Parks Canada to develop a flood protection plan for the national historic site.

The $9.2-million project will be done in three phases over two years, beginning at the end of October, according to Angelo Di Quinzio, a consultant hired by Parks Canada as project manager.

The fortress was founded by the French in 1713, but fell to the English twice and was demolished in the 1760s. When it was restored in the early 1960s, the fortress was rebuilt to meet the original specifications.

But since 1962, Di Quinzio said, the sea level has risen 20 centimetres, and is expected to increase another 60 to 90 centimetres by 2100.

"It puts the whole national historic site in a precarious position," he said.

Quay

An artist's rendition of the future heightening and extension of the Quay Wall to prevent flooding at the fortress. (Parks Canada)

In response, the federal agency will fortify the Quay Wall around the front of the fortress, and the endangered Barrier Beach, which faces the ocean.

Piles of rock protruding from the shoreline, known as groynes, will be constructed as a breakwater to protect the beach from being washed away. Fifteen-centimetre-wide "beach rounded rock" will be brought in and spread along the waterfront as a further erosion-prevention measure, said Di Quinzio. The beach work will take place from Nov. 1 until March 31.

Following the completion of that job, the east end of the Quay Wall will be raised by one metre and the wall extended to minimize the risk of flooding. The middle section of the quay will be done by December 2018 and the west end will be completed by July 2019, Di Quinzio said.

Barrier Beach

An artist's rendition of the work to be done at Barrier Beach. (Parks Canada)

Di Quinzio said there's no time to waste in getting the job done.  

"We had a flood last year," he said. "Barrier Beach showed signs of a threat to breach. If that happens, the pond behind the site would flood and consequently so would the site. We're also seeing waves crash over the Quay Wall and through the gate openings."

Discussions with the Department of Fisheries and Oceans about the best way to minimize the environmental impact on fish and fish habitat are ongoing, he said.

Di Quinzio emphasized that some of the buildings on the site are vulnerable right now since they are only a metre above the high-water mark.

"If we had a rise of [60 centimetres], that's quite significant," he said. "When you add on top of that the storm surges that we've been seeing very recently, including Hurricane Juan, we're seeing tide levels surge one metre, 1.5 metres — so this is very important work."

With files from Information Morning