To Keep Storms from Overwhelming City’s Sewerage System, Pilot Project Asks Dubliners to Install “Rain Gardens”

Reports over the summer that people couldn’t swim Dublin Bay because it was dangerous were such a shame, says Sadhbh Burt-Fitzgerald.

Burt-Fitzgerald is the co-director and acting manager of Bí-Urban Studios, a social enterprise in Stoneybatter that finds sustainable solutions to urban issues..

But that’s what happens when heavy rainfall meets the city’s overloaded water system, says Burt-Fitzgerald.

Sewage runs in the sea, she says. “And basically if you are swimming in shit, something bad is going to happen.”

Standing beside Burt-Fitzgerald in Bí-Urban Studios, at 3pm on Thursday, is her colleague Kaethe Burt-O’Dea, wearing thick-rimmed glasses and nodding along.

And in the shop window behind the two of them is what, they believe, could be a solution to this problem of dirty and dangerous water.

It’s a wooden box, three feet long and one foot wide, with the long, slim green leaves of a spider plant sticking out

The idea is that the boxes capture rainwater and the plants hold the water when the box is attached below a drain pipe, or the pipe feeds into the box, Burt-O’Dea says. That way, it doesn’t run into the already stressed water system.

Bí Urban Studios held workshops for this project. They are looking to install 200 of these boxes, or “rain gardens” as they are sometimes called, across Stoneybatter.

“It would be great to focus this in Stoneybatter at first so we could measure exactly what effect this project would have on a water system,” says Burt-O’Dea.

Says Burt-Fitzgerald: “Each individual person can just build one, create a solution to this problem and also create a really nice environment for themselves at home.”

Spreading Them Around

On Thursday, Burt-Fitzgerald had just gotten back to the shop, after putting in rain gardens around the neighbourhood, accompanied by her wheaten terrier Django.

The rain garden pilot initiative has been funded by the Local Authority Waters Programme (LAWPRO), which works with local governments and communities on issues affecting the water quality of lakes, rivers and coasts.

Burt-O’Dea lays a large white poster on the table at the front of the shop. It shows a diagram of how to build a rain garden.

Photo of rainbox courtesy of Sadhbdh Burt-Fitzgerald

You can build these boxes for next to nothing, Burt-O’Dea says. “It can be done with found materials.”

The box can be built from wood, metal or plastic, she says. “As long it can retain water.”

An L-shaped pipe is put inside the box. The bottom line of the pipe has holes in it. Rain water that trickles to the bottom of the box can flow into the pipe holes and back out of the box, meaning the box can let out excess water.

The box is layered, with plants on top of soil on top of rocks. It is put under the drain pipe, to catch the rain water as it flows down.

“The rocks hold the moisture that trickles down and then the soil can gradually intake this water for the plants,” Burt-O’Dea says.

Why Bother?

The water system in Dublin is problematic, said Thomas Carolan, the community water officer at LAWPRO, in an email.

The city centre has a combined system, he says, “meaning that wastewater and storm water go into the one pipe system to be treated together”.

“When there is heavy rainfall, which frequently happens in Dublin, the combined system is overloaded, leading to overflows into the Liffey,” he said.

Says Burt-O’Dea: “E. Coli can be introduced into these waters when this happens.” And sewage mixed with water can create methane, she says.

Methane is 25 times more potent at trapping heat in the atmosphere than Co2.

The main aim of the Stoneybatter project, says Carolan, “is to divert and attenuate as much rainwater as possible from the storm drains/combined system in an area of Dublin City”.

Liffey overflow exit. Photo by Donal Corrigan.

According to Carolan’s figures, the average annual runoff from a Stoneybatter roof is 30m3 of water. The average planter that the project is installing holds 0.405m3 of water.

If a roof has several downpipes, it would need a planter for each one, says Carolan.

Carolan says there’s no prescribed amount of rain gardens that the city needs. “The more the merrier.”

Back in the shop, Burt-Fitzgerald and Burt-O’Dea stand by their model rain garden.

“Hopefully long-term with this, we can keep diverting rainwater from going into our combined water systems,” says Burt-O’Fitzgerald.

“There is an amazing area of nature-based solutions that we should just be investing in and rolling out. They are so easy to do on a ground-level,” she says.

Past Learnings

The city has trialled rain box planters before.

Between early-2014 and mid-2015, Dublin City Council tested 11 rain box planters asa way to reduce the amount of rainwater entering sewers from existing, as opposed to new, buildings.

It cost about €225 to install each planter, said an evaluation of the trial run by Dublin City Council Beta Projects. The boxes appeared to attenuate rainwater as expected, said the final report.

“The plants have generally survived and thrived, and the solution appears to have been popular with the residents who directly took part in the trial, and also their wider neighbours,” it said.

One recommendation after the trial was to use flow monitors to accurately measure the degree of rainwater attenuation. “And also to better enable the city council to place a monetary value on the potential solution,” it said.

It’s unclear whether that was done, and why that trial wasn’t subsequently rolled out to other neighbourhoods.

One idea for a future trial was to see if food plants or herb gardens might work in the rain boxes, the post-trial report card also said.

Carolan says the plants in the boxes should be those that don’t need regular watering. “As it is dependent on the rainfall.” Try yarrow, lily of the valley, or creeping Jenny, he says.

Back at the shop in Stoneybatter, Burt-O’Dea says pollinator plants would be best.

“Go down to the canal and see what is growing by the water, these plants are perfect to plant in the rain garden,” she says.

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Author:

Donal Corrigan: Donal Corrigan is a city reporter for Dublin Inquirer. He covers transport, and the southside. To get in contact with him, you can email him on [email protected]

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