In Drimnagh, Some Residents Want to Try “Tree Pits” to Help Reduce Flooding on Mourne Road

For residents of  Mourne Road, heavy rain is more than a minor inconvenience.

The street often floods, says Ken Duffy who lives on the long thoroughfare, which meanders east to west across Drimnagh. “It blocks the way of ambulances.”

Now, residents want to trial their own solution, to plant more trees and tree pits to soak up the rainwater and ease the stress on the city’s saturated sewage system.

It’s not dissimilar to a project underway in Stoneybatter, where residents are putting planters under drain pipes to sop up water.

The Drimnagh idea is inspired by similar projects in the United Kingdom and United States, though, says Gobnait Ní Néill, who runs the Drimnagh Community Environmental Group.

“The idea is that there are lots of ways that people can participate and feel that they have agency when it comes to tackling gigantic problems,” says Ní Néill.

Padraig Doyle, a senior engineer at Dublin City Council’s Drainage Planning, Policy and Development Control Office, says it has worked with the council’s parks services to install some tree pits in the city.

They’re hoping to add more, Doyle says. “These require careful design in order to ensure that trees don’t get too much or too little water.”

A Dig Out for the Sewage System

Tree pits are only one of the many ways to capture urban runoff known as “sustainable drainage systems” (SuDS), says Doyle.

SuDS are a way to manage rainfall to minimise the bad effects of runoff, he says. “Whilst maximising the benefits of amenity and biodiversity for people and the environment.”

Such methods have been used for 20 years, he says, but the city’s next development plan – currently in draft form and out for public consultation –  adds impetus to that.

It mentions more widespread use of tree pits, green roofs, rain gardens and green walls to ease the aftermath of storms.

In the last 30 years, the number of days with rainfall greater than 0.2 mm has gradually increased, as has the number of days with rainfall greater than 10 mm, says the Dublin City Council Climate Action Plan 2019–2024.

“The frequency of extreme rainfall is expected to keep on increasing over the years, especially in the autumn and winter seasons,” it says.

Says Doyle: “It is acknowledged that there are capacity issues in the city’s sewerage system for current and future flows and this is exacerbated by climate change.”

How Useful?

Tree pits or tree beds are holes in the sidewalk in which trees can stand, says Eoin Lettice, a lecturer in plant science at University College Cork’s School of Biological, Earth and Environmental Sciences.

“They have the potential to control stormwater runoffs,” he says, depending on their size.

Some studies suggest tree pits can be cheap sustainable tools to tackle urban runoffs, he says, but they have to be big enough compared to the surrounding hard-landscaped environment.

“Pits can be a potential reserve for biodiversity, as long as herbicides are not used surrounding the trees themselves,” he said.

Ní Néill, of the Drimnagh Community Environmental Group, says she is aware that tree beds won’t be a magical solution for Drimnagh’s eco-problems.

But they’d be a small step toward building a greener neighbourhood, she says. “It certainly won’t make things worse.”

Footpaths in Dublin city can be narrow so Dubliners can’t install New York-style tree pits with big fancy railings, Ní Néill says.

“Because it will just be a trip hazard and people with mobility issues can’t get past it,” she says.

“We’re hoping to develop something very simple and encourage people to water and clear out tree beds themselves,” she said.

Why not Drimnagh?

Doyle, the council worker, says there have been pilot projects like installing rain gardens to capture urban runoffs.

But they offer only a tiny contribution to the council’s overall green infrastructure plans.

“While these have been successful, they are a very small part of our overall SuDS implementation,” Doyle said.

Ní Néill and Duffy say they would like to see more green developments like those in Stoneybatter brought into Drimnagh.

Duffy says locals have been in regular contact with the council to try to fix issues with flooding, with no luck so far. “I suspect it’s because we haven’t made enough of a nuisance of ourselves.”

Like Ní Néill, Duffy says that planting more trees with tree pits would be helpful even though he is aware it wouldn’t be a silver bullet. “I don’t know how much water they can actually absorb.”

On the western end of Mourne Road, where Duffy lives, he says, there’s not much vegetation. Greening the area is always a good idea, he says.

What matters most, Ní Néill says, is that a campaign to plant more trees and add more tree pits will unite Drimnagh locals in believing that they have the power to demand change.

“It’s harnessing all the goodwill that’s there, from people wanting to do good for their community,” she said.