The most typical modern way cities handle rainwater is to direct it to some kind of underground pipe system, and direct it out and away from the city. In some cities, there is only one sewer system, which carries both rainwater and sewage – and if there is heavy precipitation, then those systems often overflow, mixing untreated sewage and rainwater, and dumping it . . . wherever the end of the pipes is. In Portland, some of those ends are at the Willamette River. There was a massive project done here, called the Big Pipe, that aimed to reduce the frequency of those overflows (and has been extremely successful) by reducing the amount of rainwater that ended up in the pipes. Along a number of streets here, there are planting areas alongside the roads, with their bottoms below the level of the street, with cuts through their curbs to let rainwater flow in – the rain collects there and slowly seeps into the ground (there are also overflow pipes for storms when there is so much rain the planter cannot hold it all). If I recall correctly, new development in the city is required to “treat” all rainwater on site, either with a green roof or some sort of rain garden. Basically, to treat built-up areas as if they were wholly wild, allowing precipitation to be absorbed by the ground it falls on.
More and more cities are starting to do similar things, or look into ways to collect rainwater for future use; Cities are Finally Treating Water as a Resource, not a Nuisance has other examples (though not mentioned in that article is the way Los Angeles is looking to restore parts of its river, and to collect rainwater to use within the city; if I weren’t in a rush I’d go dig that up, it’s all really fascinating). Other benefits (beyond preventing sewage from ending up in rivers) are that flooding can be lessened.
“Natural” or “green” infrastructure tends to be more resilient to water stress than human-engineered infrastructure because it’s flexible; it bends, rather than breaks. The goal is to create a system that “functions as a living organism,” says Tony Wong, an early advocate of green infrastructure and founder and CEO of the Cooperative Research Centre for Water Sensitive Cities, which has hubs in three Australian cities, including Melbourne. Green infrastructure “mimics the functions of forests and wetlands and open spaces to serve and cleanse our cities,” he says.
It’s a reversal from the 20th century model that collected rain in detention tanks and lined rivers with concrete to move water away from built infrastructure as quickly as possible. That approach cut off rivers from their floodplains, raising water levels. And because concrete systems don’t flex, when they were inundated disaster struck.
It may not be possible in anything like the near term to restore all streams buried inside pipes – or flat-out buried – and let them manage the rain again, but we can at least redesign and rebuild our cities to act more like those living systems.