The Street as a Sponge

Two people walking in a street made of pavers, the road is very permeable to absorb rainwater
Reading Time: 6 minutes

Last week, I was cycling through our neighbourhood and I noticed that several gardens a few streets over have been redesigned with a lot less grass. Much has been written about the suburban North American front lawn. One could argue it absorbs a lot of water but there is not much life in them.

Twenty years ago, I saw a lot more people watering their gardens in the summer, but I rarely see people do that anymore. It is a bit silly anyway: first we go through the trouble of filtering our water so we can drink it, then we transport it through the city (pumps consume a lot of electricity) to our homes and then we water our lawn and wash our cars with it. Try to explain that to someone in, say, India (yes, I have been there).

I think this is suppose to act as a swale. The small drain holes in the red circles are not connected to a drain (at 346 Sunnyside Ave – Old Ottawa South) Google screenshot

Retaining water close to home

But with changing weather patterns it’s good to think about how to retain water as much as we can as close to home as we can, so it doesn’t all come down at once and overflows our sewer systems. The city has built more stormwater ponds, the latest one in the northeast corner of Baseline and Woodroffe: it should open soon and comes with many new trees and a new multi use pathway.

We have been gradually chipping away at our lawn ourselves, and I am hoping to turn more grass into dirt and native plants this spring. Just this week, I was reading about streets acting as sponges: “hold more water as local as possible”.

Small front yards with green space occupied by plants

Here is an article that I translated with help from Google into English about streets collecting and holding its own rainwater, the concept of wadis and planting strips of green in shopping streets, such as Ottawa’s Sparks Street or the Byward Market. You can’t just copy one on one though as the Netherlands has very soft soil, where as places in Ottawa consist of pure rock as we can observe when yet another tower is being built in downtown Ottawa.

Street as Sponge

by Gijsbert Termaat

The concept is simple: every street in the Netherlands must be able to collect its own rainwater. By strategically integrating greenery, such as trees and shrubs every ten meters, streets can be transformed from paved heat islands into green oases that absorb rainwater and provide cooling on hot days.

“I think it is a great solution to a major problem. Actually a very simple one, because planting shrubs and trees or laying grass mats is a small intervention and prevents a lot of misery. They have done that very well here and even though it is pouring rain, we have no flooding.”

Win-win situation

Bas Hoogerhuis is happy that his home on the Zuidelijke Wandelweg in Amsterdam is surrounded by greenery. “Yes, not only does it look very nice, it also prevents a lot of misery. No flooding and it is a lot cooler in summer. So a win-win situation. When it was just completed here, there was also a lot interest in this sustainable solution from abroad and there was even a Korean film crew walking around.”

Around the corner, retired Thei is planting spring plants in his garden. “Despite the abundance of green, I would like to see more color when I look out the window,” he says. “But I am satisfied with the method they applied here. They have also done this well with a so-called wadi (swale) further away, a green square in a depressed area that can fill up with excess rainwater.”

People walking on a street made of pavers. the pavement is permeable for water.
A permeable pavement retains water better: your next driveway? – LAP Landscape & Urban Design

“Luckily I keep my feet dry here with every downpour and I also enjoy a beautiful view on the beds, trees and shrubs. In short, for me this is also an example that should be followed. And what’s more, during the summers, which are getting hotter, it is also a little cooler because of all that greenery,” says Thei.

Urban planner and landscape designer Nanda Sluijsmans says that ‘using the street as a sponge’ is an environmentally friendly method that solves many problems in residential areas and shopping centers.

“Especially at a time when climate change is having an increasing impact on our living environment, this is really the way in which we have to design our streets and squares and adapt them where possible. And that can really be done anywhere.”


Sluijsmans: “Green makes living a lot more livable and it is also an environmentally friendly solution to a problem that is increasingly occurring. Nowadays we really have to deal with downpours that flood entire streets and houses. You cannot continue to watch that to happen and action is necessary.”

The urban planner proposes, among other things, to place a tree every ten meters in every street. “That is possible in 98 percent of the streets in the Netherlands. Grass tiles instead of regular tiles or asphalt can also make a difference against flooding and heat stress. Or by simply creating greenery in a ditch (wadi) and planting it with shrubs and trees. This is how you create a bathtub to collect rainwater that no longer flows into our homes and shops. Instead of wadis, we can also create rain gardens that can function the same way.”

A row of houses with a shallow body of water like a ditch, in front of them
A wadi in a neighbourhood. The water will slowly drain into the soil and is absorbed by vegetation

By planting public space with shrubs and trees, the water storage capacity increases considerably. Sluijsmans: “Roots create small openings in the ground, just like we see in a sponge. The great thing is that roots also attract all kinds of diggers, such as ants, beetles and earthworms. These provide extra corridors, and extra open spaces in the ground. This makes the soil an even better sponge.

Rain Gardens

A street with a green ribbon of trees and plants running through it
A revamped shopping street in Alkmaar. Design by Bureau B+B

The city of Alkmaar in North Holland Province already has made a first big step and created a green strip with shrubs and trees in the city centre. “Good for collecting rainwater, the greenery provides coolness on hot days and the center is now even attractive when the shops are closed.

In Tilburg they recently also greened shopping streets on a slightly smaller scale. Leiden recently introduced rain gardens in residential streets. Many cities are now making significant strides in greening and in such a way that a lot of water is collected.” Sluijsmans continues: “In fact it boils down to policymakers and city planners having to apply a green standard in addition to a parking standard. Every street needs an area of ​​greenery to function properly, to ensure that we, residents and entrepreneurs in the city, keep dry floors. Every street a sponge!”

Before and after: one of Alkmaar’s downtown streets got an overhaul with more greenspace

The Association of Dutch Municipalities (VNG) notes that all municipalities have ‘greening’ on the agenda. “But there are also matters that get in the way of this green ambition. Space in the Netherlands is scarce and creating more greenery competes with other claims on that space, for example for installing heating networks, building homes and creating infrastructure. Furthermore, municipal budgets for purchasing greenery are unfortunately often limited. And of course there must also be money to manage the greenery afterwards. We see that municipalities have structural deficits in management budgets, and these are increasing due to the increase in laying out extra greenery”, according to the spokesperson.

Check out a 2 minute video with many examples of wadis here.

Photos: Nanda Sluijtmans” check Nanda’s website here

Screenshot: Google

Text: De Telegraaf

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