The sponge city concept, and ideas about letting nature handle stormwater, don’t have to be extravagant or expensive. There are already examples of these design principles in Auckland, but they are far too limited to eliminate the impact of major storms. This can also include floodable infrastructure and parks to take the pressure off more vulnerable parts of the city. With this approach, we create spaces that better manage flooding through systems that mimic the natural water cycle. Within the sponge city concept is a way to mitigate flooding using “water sensitive urban design”. More green space and trees are also incorporated into street and neighbourhood designs. Better catch systems hold rainwater where possible and reuse it. The concept incorporates green roofs, rain gardens and permeable pavements to absorb and filter water. It’s a relatively simple idea, but a big departure from the way we typically build infrastructure. In the early 2000s, Chinese architect Kongjian Yu created the concept of the “sponge city”. There is a better way to design our built environment. It’s nearly impossible to tell how deep or fast surface flooding is, so people get into danger. Setting aside the concoction of stormwater and raw sewage flowing down streets (which we more politely call a “combined sewer overflow”), and the impact on homes, businesses and beaches, flood waters also present a massive risk to people in cars. With a huge rain event, streets quickly turn into rivers. Roads act like channels, funnelling stormwater. With thousands of miles of sealed roads around Auckland, there was simply nowhere for the water to go. The irony is that the roads themselves are a significant contributor to the flooding. It’s why, after a storm, the SafeSwim map is covered in red “high risk” markers.įrom Friday’s rain event, some of the most shocking images were of cars and buses trying to wade through flooded roads and busways. This is gross just to think about, but it gets worse.īecause stormwater is not treated, when it gets contaminated that dirty mixture drains into the water around our beaches. It’s not uncommon to see news that stormwater has mixed with raw sewage. While the system ages and suffers from reduced capacity, it is also more prone to failure. This is what the contested Three Waters project is really all about, and we need to quickly get past the political sideshows it has inspired Modernising all the stormwater infrastructure will take decades and billions of dollars. With age, the system’s capacity to capture stormwater significantly declines. Add an abnormal amount of rainfall, and neighbourhood flooding is nearly guaranteed.Įven if the way we’ve built our cities and the stormwater system could keep up with big storm events – to be clear, they cannot – the network of basins and pipes is aging. While every block typically has a catch basin or two, they can easily clog with leaves and other debris even before a storm hits. The network of pipes can only hold so much water before it is fully inundated and begins to flood. Every new building or road replaces the planet’s natural stormwater system: plants and soil, and channels for runoff. The more we build, the more stormwater we need to drain. From the gutters, the water drains into a stormwater catch basin, through the stormwater network, and into streams and the sea. When it rains, the water rushes off these surfaces and into gutters. While almost no city in the world could fully escape the effects of four months’ worth of rain in 24 hours, there are many things that could have been done to avoid some of the worst impacts.īuildings, streets and car parks are all impermeable surfaces. We’ve built our cities to be vulnerable to – and exacerbate – major weather events such as the one we saw in Auckland on Friday.
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