Restoration at the head of Liffey should reduce flood risk downstream for Dublin city

Marcus Collier always warns his students before heading for the start of the Liffey River: bring wellies.  

The blanket bogland in the northeast of the Wicklow Mountains can be deceptive. Puddles look crossable even in wellies but can sink much deeper, says Collier, associate professor and head of botany at Trinity College Dublin.

Grassy mounds are more firm, he says. 

Purple heather and green moss stretching across the autumn mountains were relatively dry underfoot on Friday. Squishy, spongy, but safe to walk on. 

Collier took a bouncy step on the bog. The ground quivered, at least a metre away. “If this was a really wet bog, if I jumped here, somewhere, about 10 meters would wobble,” he said.

Re-wetting the land here is a project underway in the Wicklow Mountains, at the start of the Liffey, the main water source for Dublin.

Collier was nearing the start of the river, which flows on from here west towards Newbridge, before turning towards Lucan and looping down into the city and then emptying out into Dublin Bay.  

Up here in the mountains, the river starts as trickles through squishy bog. 

Further down, much of the flow of the river is controlled by a dam and reservoir operated by the ESB at Pollaphuca. But the more natural water storage of the peatlands has started to attract attention and funding in recent years.

"The simple thing is, protect this, and you protect the city," Collier said.

Bogs and flooding

Improving the health of the natural landscape of the start of the Liffey should improve the water quality and help manage flood risk downstream in Dublin, says Collier.

The Wicklow Mountains already bear the battering of storms before they reach Dublin, Collier said. 

Building up the landscape’s capacity to absorb water can mitigate flooding further downstream, he said.

“Anything that can be done to improve the uplands,” Wilson said. “[Where] peatland then absorbs the water and releases it slowly … downstream of that the flood risk [will be] mitigated.”

The interventions are relatively small too, he said. “It's just good old fashioned – get in there, put little mini dams in, block up the drains, and let the bog do its own thing,” Collier said.

How effective bogs can be in mitigating flooding depends on the bog, and its history.

The government’s National Peatland Strategy 2015–2025 commits to looking at the viability of “cutaway peatlands” – those where the most or all of the peat has been harvested – for flood attenuation measures. 

A progress report on the peatland strategy in 2017 said that a study looking at using Bord na Móna bogs for flood storage – which focused on the River Shannon – “calculated that the potential available storage will have an insignificant change in peak water levels for the 2 year, 10 year and 100 year flood events”. 

“The reason for this is that the storage available is insignificant in relation to the volume of flow in the River Shannon,” it said. “Accordingly, this flood risk management measure was found to be technically unviable as it had an insignificant impact on peak water levels in all flood events.”

But the bogs around the River Shannon, and this one in the Wicklow Mountains is different, says Collier.

Around the Shannon there are “cutaway” bogs, lowland bogs where the peat has been industrially harvested to one degree or another, and lakes tend to form. 

But the Liffey Head Bog is a highland bog, which has not been harvested on an industrial scale, and can absorb a good deal of rain.

Restoration

The restoration of the Liffey Head Bog is a National Parks and Wildlife (NPWS) project in partnership with Intel. 

Their collaboration started in 2021. At the time, a statement announced that they aimed to restore 60 hectares of peatland – 1.5 percent of the 4,000 hectares of degraded blanket bog in Ireland.

Now there’s small wooden and metal barriers through the small valleys in the bog, blocking the water from drainage so the bog will hold more water.

“Intel is committed to restoring water in quantities greater than the water it consumes,” says a government press release about the project.

The organisers of the Transport Research Arena 2024 conference – the European Commission, the Department of Transport, and Transport Infrastructure Ireland – launched a €600,000 peatlands rewetting project to restore 100ha of peatland in the Wicklow Mountains.

The results of restoration of this kind of habitat are slow and the impact of these projects will take time to be perceptible too, said Collier. 

The landscape restoration is cheap, natural, and effective, says Collier. It doesn’t require big machinery, which can trample the landscape.

And the results offer a “triple win”, Collier says. “Carbon capture, flood prevention, and then biodiversity conservation,” he says. 

According to the European Investment Bank, restoring the Irish peatlands “has the potential to reduce national carbon emissions by an order of 5-10 %”.

David Wilson, a research scientist at University College Dublin who studies peat restoration, said this project at the Liffey Head Bog tracks with other projects to rebuild Ireland’s natural landscape.

“It's a very inexpensive and elegant solution to fixing a multitude of problems, not least, you know, water quality, carbon, climate, wildlife, and it is becoming more mainstream in the last number of years,” said Wilson.

Collier said sure, maybe tech companies getting involved in peatland restoration could be greenwashing. 

“I suppose that could be the case,” he said. But “if it gets peatlands restored it’s a big win for nature and carbon”.

“Win-win”

On the bog in the Wicklow Mountains Friday, Collier pointed at the slow trickle of water through colorful moss and small shrubs and dark earth.

“We're standing at the side of the Liffey here, right here, it's going nice and slow,” he said. “And the peatlands that it flows through and comes from keep this water slow.”

He said that’s the goal basically: bog loves water. Give it the right dynamic to take it in.

Otherwise, says UCD’s Wilson: “When there is a downpour, the water immediately leaves that site and gets into the streams, leading to potential flooding.”

“And in combination with that, when the water leaves the peatland under such extreme and fast circumstances, it brings with it a lot of peat,” said Wilson.

Not only does that make the water browner, it will need more chemicals to clean it, he says.

“There's a lot of particulates in the peat, and that has an effect on the wildlife within the rivers downstream. It also causes issues for water that comes out the tap for consumers,” he said. 

So restoring the bog’s ability to hold water and rebuilding peat is a “win-win for everyone”, he says. 

“If you can restore, recuperate, rehabilitate a lot of these damaged sites further upstream to prevent flash flooding and prevent loss of peat into the water and rivers,” said Wilson.

Push and pull

It’s one thing to do restoration on publicly owned land but it’s another when it’s private land in Wicklow, Collier said as he jumped over a small channel of water flowing through small brown and green brush Friday.

“There's been a certain amount of resistance to it in recent years, particularly by farmers who object to the idea that they should be forced to re-wet plains that maybe generations have spent draining,” he said. 

Wet land isn’t good for farming – which in the Wicklow Mountains is basically sheep farming – the farmers want firmer land.

But for neighbouring land, peat also holds the water and decreases flood risk, according to 2016 research by Water Resources Research, and 2017 research by Friends of the Earth.

Over the last decades, Wilson said, peat restoration has become much more popular, better funded, better organised, and more well-defined.

More companies have been financing it since the introduction of the Peatland Standard for Ireland, which creates a certificate to verify environmental benefits from restoration, he said. 

These standards, Wilson said, are “guidelines that will allow anybody considering funding and financing restoration, confidence that the work will be done to a standard that's universally or applied”. 

“This was a huge step forward, because prior to that, everybody was doing their own thing, and there was no real confidence for investors coming in, you know, to put their money in and know that they were going to get a set outcome,” said Wilson.

Wilson said he thinks “we’re on the cusp of something that could be a greater uptake”. 

“Now there's no shortage of damaged peat in the country to restore,” he said, “There’s great scope there for restoration across the country and not least around the Dublin Wicklow area.” 

Funded by the Local Democracy Reporting Scheme.