As the climate changes, communities across the world will need to adjust to new weather extremes. For some, that will mean building resilience to droughts or heatwaves, or making sure that residents are briefed on what to do in case of hurricanes. For others it will means flood preparedness, investing in flood defences and soakaways.
Built up urban areas are vulnerable to flash flooding because pavements and roads aren’t permeable, so water runs off faster than drainage systems can handle overflows into the streets. We’ve all experienced flooded streets when a the sudden downpour of a summer storm outruns the capacity of gutters and sewers. Heavy rainfall is more likely as the climate warms. We can’t stop it raining, but we can make sure that cities are built to handle water better.
Rotterdam is a city that knows it is more vulnerable than most – it is a coastal city that is below sea level in parts. It has developed a detailed water plan to protect itself from the double challenge of heavier rain and rising sea levels. It is planning to deliberately allow flooding in certain areas of the city, collecting water and discharging it at a slower rate. The plan includes roof gardens and green roofs that will absorb water, and even buildings that float. The particular innovation I wanted to mention today is the water plaza.
During dry weather, the plaza operates like any other public square. It’s a place for people to meet and hang out. There are steps that people can sit on, making space for public performances, sports, or special events. When it rains, water from surrounding streets is directed into the square, which fills up. This pools the water, relieving pressure on surrounding drainage. The square then drains at a much slower rate through a central point. There are filters fitted on the drains feeding into the plaza, so that it won’t fill up with dirty water.
The plazas are also designed in levels and channels, so that rainfall actually adds to the appeal of the square, opening up little ponds, rivers and water features. Only a really big storm would fill the whole thing and take it out of action entirely. The images here show the same plaza dry and full above, and partially full on the right.
Water plazas can be placed in strategic places around the city and take different forms. In some areas they might be public squares, but the idea could be equally applied to playgrounds, skateparks or basketball courts. (Check out this short video to see how those can be combined, too. It’s in Dutch, but you’ll get the idea) The principle is the same – creating holding areas that catch water and soak it away in more controllable ways.
All new developments in Rotterdam will be expected to include stormwater buffers in some way. It’s a great example of resilience planning as well as smart design, and many other cities will need these sorts of strategies in the coming years as we adapt to a changing climate.