'Dunes don't care,' but humans need to adjust to retreating shoreline

P.E.I.'s dune system will be fine despite the damage from storms like Fiona — but people need to get out of the way, according to two climate change researchers.

Geologists Robin Davidson-Arnott, retired from the University of Guelph, and Jeff Ollerhead of Mount Allison University have been studying the dune system at Greenwich in P.E.I. National Park for 20 years, and put it in the context of millennia of change.

"Sea level's been rising in this area for more than 5,000 years," said Ollerhead.

"If sea levels and storms by themselves were going to destroy the dunes, there wouldn't be any dunes now, but yet there are. So they will continue to adjust."

The damage to the dunes caused by post-tropical storm Fiona last month was severe — in some areas, almost 10 metres of dune was cut away as if with a knife, leaving Islanders mourning the loss.

At Greenwich, Ollerhead and Davidson-Arnott found less damage than they expected, with about three metres of dune sliced away. But the sand hasn't entirely disappeared, and their experience tells them the dunes will recover.

"It doesn't matter to the dunes, you know. The dunes don't care," said Davidson-Arnott.

"The dunes are just magnificent. They withstood it quite happily and they will grow back."

Natural migration

They won't, however, grow back exactly where they were. The dunes have been retreating inland, and will continue to retreat, they said.

That retreat is not uniform. In calmer years the dunes will advance forward on the beach, and then be knocked back by a major storm like Fiona or a series of winter storms. In their current condition, with little vegetation left on the foredune, more sand is loose and will blow over the top, building up the hind part of the dune. The newly-carved sand cliff will collapse onto the beach, and the dune will be re-established a little further back from where it was.

"If there are more storms it just means that we will see the dunes in that very steep slope much more of the time," said Davidson-Arnott.

The exception is where the dune runs into a barrier.

"Places along the shoreline where we've either built roads or walls other hard impediments that don't allow for migration," said Ollerhead, "that's when they will cease to survive because they have nowhere to migrate."

'Nature usually wins'

The sand doesn't go away. It will move along the shore and build up dunes in other areas, but the dune in that particular area will be gone.

That, the researchers pointed out, is a problem for any human infrastructure that was built behind it.

The dunes provide a natural barrier between the sea and the land. When a dune disappears anything behind it becomes vulnerable.

"People want to see it put back the way it was before the storm, but in fact real success is maybe not putting it back the way it was before the storm. Putting it back in a way where it's ready for the next storm, which, as I say, almost invariably means moving things back a little," said Ollerhead.

"You should probably think about how to work with nature rather than against it, because in the end nature usually wins."

P.E.I. has very weak bedrock, they said, and the sandstone and shale will continue to erode. There is no way of stopping it, and people will have to find a way to deal with that.