The tip of Bull Island has been slowly disappearing

The northern tip of Bull Island is eroding, scientists and locals say.

“We’re losing a lot of [it],” said Mary Tubridy, an established Dublin-based ecologist, “and the chances are, we'll be losing more of it.”

“The sand dunes have kind of been eaten away. And there’s this kind of big bite being taken out of them. There’s a kind of cliff of sand,” she said.

Sean Byrne, a member of Bull Island Action Group, a group of volunteers who clean up the island, said he’s noticed it too. 

“Erosion has speeded up in the last few years,” Byrne said. “Mainly after those big storms when you get a very high tide. It comes right up to the dunes and washes part of them away.”

The low lying island in Dublin Bay – off Clontarf, Kilbarrack and Sutton – is home to two golf courses, dunes, and wide sandy beaches. 

It’s a special protection area for the conservation of wild bird species, and one of the 714 biosphere reserves – “learning places for sustainable development” – in UNESCO’s World Network of Biosphere Reserves. It also hosts two nature reserves.

Fundamentally, Bull Island is made of sand, said Iris Möller, who leads Trinity College’s Coastal Research Group, and is a Professor of Geography. So it is always shifting and changing, regardless, she says.

The erosion on the northern end of the island started around 2013, said Möller on a video call recently, sharing a graph made by a former graduate student showing that part of the island losing sediment.

This has the potential to impact the protected habitats and creatures who live on the island, says Green Party Councillor Donna Cooney, who is on the Bull Island Oversight Forum.

There should be better monitoring of how the island is eroding and shifting and changing, say Tubridy, Cooney and Möller.

"Once we understand how it's changing, we have our early warning system,” says Möller.

200 years old

Bull Island itself formed because of harbour engineering works in the early 19th century. 

When the North Bull Wall was built about 200 years ago, to keep sand away from Dublin Port, it changed tidal currents and caused sand to accumulate behind the wall, Möller said. 

Over time, dunes formed, she said. “North Bull Island started as a sand shoal, and then it grew upwards because it had enough accumulation of sand to allow sand dune grass to become established,” she said. 

Grass grew, which trapped more sand, and helped build up the dunes, Möller said. “But dunes only persist if enough sand continues arriving,”

It’s normal for sand to move, she said. But she said, right now, scientists aren’t entirely sure where the sand feeding Bull Island is coming from, and that’s something they need to figure out.

Sea-level rise is also affecting the system. “It looks like in Dublin it’s at least six millimetres a year at the moment,” Möller said.

Dublin Bay rose at a rate of 6.48mm/year from 1997 to 2016, according to Gerard McCarthy, an oceanographer at the Irish Climate Research and Analysis Unit (ICARUS) at Maynooth University.

[We will link this story in here: https://www.dublininquirer.com/sea-level-in-dublin-bay-is-definitely-rising-fast-confirms-irish-research/]

Higher sea levels mean sand is more often underwater, which prevents wind from picking it up and moving it into the dunes, Möller said. 

“So you are then having a battle between that and then the sand on the beach that needs to be high enough to be carried by the wind is the issue,” she said.

Stronger storms can also strip sand away faster than it can rebuild. 

“The island really struggles to heal itself,” she said, especially when storms occur in quick succession.

Byrne, of the Bull Island Action Group, says he’s noticed this too, while down on the island.

“Mainly after those big storms when you get a very high tide, it comes right up to the dunes and washes part of them away,” Byrne said. 

What’s the impact?

There’s a few problems with the island eroding, says Cooney, the Green Party councillor.  

It could interrupt habitats: for seals, rare species of birds, a rare orchid, and other living things on the island, she said.

“That’s where the seals rest with their pups,” she said, and nearby dunes also host ground-nesting birds, some of which are endangered.

Says Tubridy: “It's a very good food source, sheltered and safe, and there's lots of protection of the birds as well in that area.”

Bull Island also acts as a natural barrier that reduces wave energy entering from Dublin Bay, Möller said.

“If you lose the tip on North Bull Island, and it were to separate… then you have a much wider gap between Howth and North Bull Island,” said Möller.

That would allow stronger waves to crash against the shore. “More energetic waves [would come] through that gap,” she said.

That could increase pressure or erode coastal defences such as the Clontarf Sea Wall, and raise flood risks during major storms, she said.

What to do?

The main thing needed, Cooney, Möller, and Tubridy each brought up independently, is money for consistent monitoring and reliable data of the erosion of the island.

The Office of Public Works (OPW) has done coastal LiDAR monitoring, and Trinity has done drone surveys, Möller said. 

But there’s no dedicated budget line for tracking how the island’s dunes and sand volumes are changing over time, she said. “The fact is, we do it sporadically.”

“We have, you know, very little funding available, and we have to apply for it. Then we get a student who might do a project one year,” she said. 

It’s not clear what would actually effectively stop the erosion, Tubridy said. 

“I suppose it's just inevitable,” she said, and paused. “It’s interesting … evidence of climate change.”

“And I suppose at the least, we should be monitoring that,” she said. “You know, there should be some effort to try to record what we're going to lose.”

Cooney agreed that more funding is needed. “We need a budget line that allows us to properly understand how the coast is changing,” she said.

Better data, Cooney said, would help scientists and planners know whether conservation measures are working.

“If we put in man-made measures to protect the island, we need to be really, really careful that we don't actually do the opposite to what we want,” she said.

Funded by the Local Democracy Reporting Scheme.