The world’s cities and population centers are overwhelmingly located near water. This makes good sense since water is essential for living, and throughout history, people have built their settlements where water is accessible and in abundant supply. However, in recent decades the vital good that water offers has become complicated by the climate crisis as sea levels rise and flooding in river systems become more severe.
Perversely, increased precipitation and drought go hand in hand. More and more often cities are experiencing flooding and then endure periods with water shortages. This is due to how we’ve built cities over the last century – using impermeable, flat surfaces like concrete, which are designed to let water flow away, and be drained out to sea – which also leads to toxic storm runoffs as well as contributing to storm related flooding.
The good news: Many cities are finding that the solution isn’t in getting rid of the water. Rather, it’s to soak it up.
The idea is a simple and elegant solution: store the excess water to use later.
A variety of methods help create a new-age city called a Sponge City, also known as a Porous City, or using the blue-green infrastructure. Urban developers and researchers around the world are moving away from concrete walls, culverts, and sewage systems toward building green roofs and parks, restoring wetlands, swales, and rivers, and digging storage ponds.
Sponge Cities aren’t meant to get rid of the water, they’re meant to slow it, avoid the runoff, and store it. It has become a national ambition of some countries like China, which experience increasingly severe floods with loss of human life and property damage. Some cities are already way ahead in implementing sponge techniques. Here are a few:
Despite what it might be better known for, Wuhan is also known as “the city of 100 lakes” and has a lot of experience with flooding due to its proximity to the Yangtze River. It has become one of China’s pilot sponge cities. 390 infrastructure projects have been built in Wuhan for this purpose, including a massive project of adding green space along the Yangtze. The city has added Vegetation and permeable surfaces for more than four miles, in addition to 45,000 trees, 125 square miles of shrubbery, 150 square miles of grass, 15 soccer fields, and seven swimming pools. The parks also now sequester 725 tons of carbon dioxide a year.
Engineers in Malmo began efforts to separate stormwater runoff from wastewater in the 1990s to prevent the sewer system from overflowing. In doing so, they also helped themselves avoid disastrous flooding by creating a series of concrete canals with the capacity to hold enough water for an epic one-in-25-year flood. The canals lead to ponds which are layered with artificial “stones” to slow flow and create small vortices, allowing for oxygen to help plants grow. The water passes along to other ponds, through marshy areas, allowing the water to be safely distributed.
The City of Brotherly Love’s “Green City, Clean Waters” plan set a goal for the city to reduce its 13 billion gallons of runoff water, as part of the Clean Water Act. It’s already on its way to achieving its goals, having utilized green architecture throughout the city, such as rain gardens, green roofs, and the restoration of wetlands. The Philadelphia Water Department emphasizes that the key is integrating pieces and parts of the city to work together, using different places for different functions as needed.