Pour it on: How Dutch cities are soaking up rain and reducing flooding
This is the fourth nstallment of a Times-Picayune and Advocate series exploring how the Netherlands’ climate change adaptation strategies could be a model for the Louisiana coast.
The series was produced in collaboration with WWNO New Orleans Public Radio and Climate Central, and is part of the Pulitzer Center’s Connected Coastlines reporting initiative. For more information, go to pulitzercenter.org/connected-coastlines
By Tristan Baurick, The Times-Picayune | New Orleans Advocate and Climate Central
ROTTERDAM, The Netherlands— Eveline Bronsdijk knew she'd done her job when the people of Rotterdam began debating whether pigs should be allowed on rooftops.
In 2012, Bronsdijk, the city’s sustainability adviser, was trying to promote green roofs, thin layers of plants that make buildings cooler, the air cleaner and — most importantly for Rotterdam — gutters and storm drains drier.
At first, she touted how much rain the roofs can absorb, and how they could play a role in reducing the city’s increasingly chronic flooding problems. “But people don’t care about those technical aspects,” she said. “They thought it’s nonsense. Why invest in something above your head that you can’t see? Duh! End of story.”
Then she showed them the flowers and vegetables they could grow, and the tiny rooftop farms they could create with beehives and chicken coops. That’s when the city’s voluntary green roofs program took root. “People said ‘OK, we have chickens, but now can we have pigs?' Some people hated that idea. When local groups started to fight over pigs, it was proof of success. They had embraced the fact that the roof was not empty space.”
Now Rotterdam has more than 100 acres of rooftop greenery. That’s enough to coat nearly every roof in New Orleans’ Central Business District with rain-absorbing vegetation. Rotterdam’s green roof initiative is one of a growing number of projects in Dutch cities that aim to capture and store rainwater while also making urban life more livable.
“We are now in an orchard, and before we were in a field,” Bronsdijk said while walking through a park on top of an old train station. The long roof boasts at least 50 apple and pear trees, several community vegetable garden plots and a large lawn used for festivals.
For lunch, she stops at a restaurant on the top of a seven-floor office building. The artichoke in the soup, the edible flowers in the salad and the honey in the tea all come from the rooftop farm outside, one of the largest in Europe.
“You have to show what’s possible,” she said. “And you have to have a fun approach and then people will really embrace it.”
Like New Orleans, Rotterdam is coping with heavier rains and bigger storms brought about by changing climate. Over the past century, precipitation has increased by more than 20% in both the Netherlands and the American South, and the rain is tending to come down in heavy bursts that overwhelm old drainage systems. In New Orleans, it's becoming clear that the city’s century-old pumps can no longer keep up with today’s downpours, causing increasingly routine flooding in areas that had little trouble draining a few years ago.
New Orleans architect David Waggonner has for years been calling on the city to find more ways to hold or slow the rain temporarily until the pipes and pumps can catch up.
“The idea that you’re going to pump this city out — I don’t think people hold that anymore,” he said.
Waggonner helped write the Greater New Orleans Urban Water Plan, an ambitious, Dutch-inspired series of strategies for creating public green space, opening up more canals and other upgrades aimed at retaining or slowing water to give drainage infrastructure time to catch up.
Nearly a decade later, the plan, which lacks a funding source, has inspired a smattering of small improvements — a few rain gardens and strips of porous pavement. In Dutch cities, similar efforts that began around the same time have been systematic and wide-reaching.
Becoming 'a bathtub’
Rotterdam has always been a heavyweight in the battle against water. A greater share of Rotterdam than New Orleans sits below sea level — some 80%, and some of it by 19 feet. On all sides, water is trying to get in. The Rhine, Schedlt and Meuse rivers merge in its city limits and flow to the North Sea, less than 20 miles away. River flooding and storm surges have been adversaries since Rotterdam was founded nearly 800 years ago, and yet it’s grown into the Netherlands’ second-largest city and Europe’s biggest port.
Rotterdam’s levees, floodwalls and the immense Maeslant Barrier, one of the largest moving structures in the world, are effective in keeping out water from rivers and the sea, but not from clouds.
“We have made ourselves into a bathtub, and now it’s filling up,” Bronsdijk said. “We have a lack of space underground to increase our (drainage) system, so have looked up at our roofs.”
Rotterdam’s green roofs initiative started with subsidies that required a certain amount of rainwater retention, usually about 4 gallons for every 10 square feet of green roof, for a reduction in taxes and other fees. The city offers guidance in green roof design and educational events. The largest event, Rotterdam’s annual Rooftop Days festival, draws thousands of people to more than 60 green and multifunctional roofs.
The green roofs have become numerous enough that they are promoting themselves, allowing the city to up the ante for subsidies. Starting this year, a qualifying green roof must be designed to retain twice as much water — about 8 gallons for every 10 square feet — as when the program began in 2008.
“When you have roofs like these, you can invite people and show them it catches rain and say, ‘See the yellow flowers you can grow,’ ” Bronsdijk said. “And they say ‘Yes, well, I like pink. Can I have pink flowers on my roof?’ ”
Likewise the jump from chickens to pigs, which the city did eventually decide to allow on rooftops. In a concession to animal rights groups, the pigs have to be kept away from the roof edges so they’re not spooked by the heights.
Rotterdam’s 100 acres of green roofs have boosted the city’s water storage capacity by at least 1.6 million gallons. That’s the equivalent of about 40,000 bathtubs.
The city plans to more than double its green roof coverage over the next decade. With the higher water storage demands that began this year, the city could retain upward of 5 million gallons of rainwater in its rooftops by 2030. That represents a small fraction of the rain that might fall on the city during a storm, but the goal is to ease pressure on the drainage system, not catch all the city's precipitation.
Besides storing rain, green roofs are credited with a host of other benefits. They provide habitat for plants, birds and insects that might otherwise have limited natural space in urban areas. They improve air quality thanks to plants’ ability to filter pollutants. While traditional roofs and other hard surfaces, like streets and parking lots, raise temperatures, green roofs have the opposite effect, cooling ambient temperatures by 5 degrees and cutting summer air conditioning costs by 7%.
Increasing the number of green roofs can reduce the ‘heat island’ effect that makes gray, hard urban areas several degrees hotter than the greener, softer spaces outside cities.
“Green roofs have a real cooling effect, which could really be useful for a warmer place like New Orleans,” Bronsdijk said.
Louisiana may be better-suited for green roofs than the Netherlands. That’s because green roofs perform best when rain is followed by warm, sunny periods, which increases the rate of evaporation, according to a Hague University of Applied Sciences study. This ideal pattern of rain and sun matches New Orleans weather better than the cloudy and cold climate of Rotterdam.
And yet, New Orleans has only a few green roofs. One of the most prominent ones covers the Sewerage & Water Board headquarters on St. Joseph Street in the CBD. It was proclaimed the city’s “first public green roof” when it was installed for $324,000 in 2016. But it’s off-limits to the public right now: The S&WB declined a recent request to see it. An official said it is undergoing replanting and won’t be available for viewing until spring.
‘It’s the way to go’
Rotterdam isn’t leaving the job of catching and holding all the city’s excess rainwater entirely to its roofs. Another widespread rain-retention strategy has been to build dual-purpose public water plazas. The recessed, below-grade sections of the plazas temporarily collect and store runoff during heavy rains. On dry days, the plazas are basketball courts, school playgrounds and skate parks.
It’s most prominent is Benthemplein water plaza, sandwiched between two schools and a church. It can store nearly 480,000 gallons of water channeled from a parking garage and several roofs — nearly one-third the total that Rotterdam’s green roofs can store.
The city has built 10 water plazas in recent years, and five more are planned by 2023. It’s now standard practice to consider installing them whenever the city rips open the ground to improve drainage.
“We replace pipes every 60 years,” said Johan Verlinde, Rotterdam’s climate adaptation manager. “When we tear it all up, we think, ‘How will this area handle future storms?’ And then we ask citizens in that area, ‘What do you want here?’ Sometimes it’s a soccer field; sometimes a schoolyard.”
In the end, neighbors get new pipes and a new amenity that also happens to reduce flooding.
These concepts, which the Dutch collectively call ‘living with water,’ don’t come cheap. Building everything in the New Orleans water plan would cost upward of $6 billion — 36 times what the Sewerage & Water Board, which manages New Orleans’ drainage system, spent on capital projects last year. Such an undertaking wouldn’t be as hard in the Netherlands, where citizens pay high taxes and have strong faith in local government.
New Orleans water managers enjoy neither of those advantages, said Ghassan Korban, the S&WB’s executive director. He recently toured Rotterdam’s green roofs and water plazas. He liked what he saw, and he says he loves the New Orleans water plan, but the only way to come close to paying for it is with a new stormwater fee.
“It’s the way to go,” Korban said. “I think it’s the only steady and long-term way to fund a robust and reliable drainage system in the city. But we’re at a point where we need to gain (the public’s) confidence.”
Korban took over the beleaguered S&WB during a rough time. Several top-level staff were fired after misleading the public about the number of broken and inoperative pumps during rain flooding in 2017. The pumps are still having problems. A turbine powering pumps exploded in December. Catch basins and drains are reliably clogged. When a car was pulled from an underground drainage canal in August, it made national news. Most New Orleanians shrugged.
Korban knows his agency’s reputation isn’t stellar. The S&WB needs more money, but it doesn’t have the public support to ask for it, Korban said.
“We need to grow it,” he said.
A large share of New Orleans’ drainage woes stem from a reaction-based approach to basic maintenance and inspections. Pipes aren’t checked unless they clog. They aren’t fixed until they fail.
Bronsdijk’s face clouded with confusion when told of this approach.
“That is an interesting way to do things,” she said. “But why do you do this? If you cannot care for what you have, it is hard to do anything more. You are always fixing old problems.”
WWNO New Orleans Public Radio reporter Tegan Wendland contributed to this story.