How Cities are Rebooting Themselves for intensive rains and Floods with Sponge Cities
Yanweizhou Park in Jinhua City
(2 billion people)
Reading Water Always Wins led me to read articles by Adele Peters and Poornima Apte.
Since the 1700s, we’ve filled or drained as much as 87% of the world’s wetlands, which would otherwise be flexibly absorbing and releasing water. The land area lost to cities has doubled worldwide since 1992. In dense cities, only around 20% of rain infiltrates the soil. Instead, drains and pipes carry it away—lunacy, Yu thinks, in places with water shortages.
On New Year's Eve, during the intense storm, a small Japanese restaurant, Izakayarintaro, in the Mission District employees, had to crawl out of a window as the kitchen filled with water after 5.5 inches of rain wreaked havoc.
Atmospheric rivers, which carry 15 times as much water as the Mississippi River, aren’t new on the West Coast, but the number of atmospheric rivers may double by 2100. The “trillions of gallons” of water being dumped on the state are not being captured for later use. The flooding is compounded by sea level rise and skinking land in some areas.
Better urban design for water could help. Sponge cities, a name dubbed by architect Kongian Yu,” who helped redesign, can absorb rainwater instead of letting it flow through miles of pavement to the ocean carrying waste. From Iowa to Vermont and San Francisco to Chicago, urban infrastructure is getting a reboot.
In Seattle, reservoirs are being created in city parks. A new channel will lead extra water to the city lakes. Neighborhood rain gardens help soak up water to avoid overloading the sewer system. Sunken gardens double as rainwater storage. “The Dutch city of Rotterdam, a sunken basketball court can store nearly half a million gallons of water in a storm,”
As Cities develop, miles of impervious pavement are laid over forests or wetlands, displacing the natural flood management systems like creeks, underground streams, or bogs. In an entirely uninhabited landscape, rainfall enters into the natural water cycle in four different ways: it either soaks all the way to the ground and becomes groundwater; runs down valleys into bodies of water and finds its way to the sea; it is taken up by plants; or just evaporates. In urban or suburban areas, water has nowhere to go so every heavy rain can turn into a flood.
It is estimated that 83% of the U.S. population lives in urban areas, up from 64% in 1950 (css.umich.edu)
“Rain Gardens, Bioswales, and Porous Pavements” are artificial solutions. Richard Willis, Director of Pavement Engineering and Innovation at National Asphalt Pavement Acco, says: There is little room between the particulates, thus no room for rainwater…. The construction industry gap measure for pavement is described by the term “air void,” which is set at 4% for the traditional pavement mix, says.
One way to make cities spongier is to use permeable pavements, porous asphalt made with many larger stones, and added cellulose fibers to hold the porous asphalt together. Porous pavements are typically laid on top of stabilizing material and a gravel layer, which functions as a reservoir to hold and eventually disperse the water into the soil underneath. Because water trickles through the top layers of porous pavements faster than through the traditional pavement, studies have found that winter de-icing budges have the potential to be lower.
Native plants help soak up rainwater. House spouts can empty into rain gardens instead of a sewer. A bioswale is a rain garden on a larger, more engineered scale. James Stitt, Sustainability manager with the Pittsburgh Water and Sewer Authority, states water retention is facilitated by several factors dealing with either soil medium and containers called R-tanks - a container akin to plastic milk crates that can be stacked like Legos underground, capable of bearing large water loads, releasing it slowing into the surrounding soil.
More Success Stories: In Palo Alto, a creek is embedded in a concrete channel; the firm is working on a design to return it to a natural state, creating a more extensive area for water to soak into the ground and new access to nature for people nearby.
A rain garden is a depression in the soil s
In New City, after rain from Hurricane Ida and Tropical Strom Henri flooded some basement apartments, the area in the front of one apartment building stayed dry. A “living street,” built with permeable pavement that can suck up water, helped prevent flooding, along with rain gardens around the building.
Street pavement could be transformed with the same principles: A parking lot could become a park, rain gardens could border bike lanes, and the street could be lined with trees to capture large volumes of water via their roots.”
SF has been building green infrastructure projects. 14 blocks of Sunset Blvd are lined with rain gardens. Holloway Ave has eight blocks of permeable pavement and bio-retention planters (curbside planters designed to capture water.)
City park districts are “daylighting” underground channels in above-ground creeks, bringing it back to the surface where it could capture rain that would otherwise flow to the sewer system and out to the ocean.
Pittsburgh, Chicago is an example of a Steel City that struggles with stormwater management. This aging infrastructure served to store and sanitary flow when barely an inch of rain fell, discharging raw waste into local waterways. Pittsburgh opted for a sponge city plan mimicking the natural hydrology of an area, including rain gardens and bioswales in the design. Natural non-engineered infrastructure was created in Seattle and San Francisco, which removes invasive species such as English Ivy and Himalayan blackberries, restoring native evergreens that do a better job of stormwater retention. The trees act as a natural filtration sponge, reducing waste and rainwater during rainy seasons. Rain gardens and bioswales have the added benefit of being aesthetically pleasing. Roof Cisterns for water recapture are another method. A 1,200-square-foot roof would yield approximately 750 gallons of water from a 1-inch rain.
Sarah Colenbrander, Senior Researcher at the Longdon-based International Institute for the Environment and Development, says urban wetlands and woodland are being restored. Still, the biggest stumbling block, according to Postel, is scalability. Can one-off examples work on a sizeable country-wide scale? That can only happen with a significant boost from policy implementation, which needs to be from the top-down legislation.
The world needs to rethink its cultural expectation of what a prosperous city looks like. Where people live much more densely and have communal green space…you have less of an ecological footprint. A holistic approach ensures that zoning boards, the parks departments, and the transportation board participate in the same planning discussion. Despite difficulties, sponge cities are becoming more prevalent. Chicago has instituted green roofs and bioswales, as has Philadelphia. The twentieth century was the age of dams, diversions, and depletion. Postel writes that the 21st Century can be the age of replenishment when we apply our ingenuity to living in balance with nature.
Article file links JSTOR, By Poornima Apte December 5, 2017. How to Build a City that Doesn’t Flood? Turn it Into Sponge City,
Erica Gies, December 21, 2021, Water Always Wins: Thriving in an Agen of Drought and Deluge, https://www.technologyreview.com/2021/12/21/1041318/flooding-landscape-architecture-yu-kongjian/file:///C:/Users/Maureen/OneDrive%20-%20mcmrealty.org/Prisideo%20Grad%20School/SSSJ/Discussion%20Forum/How%20to%20Build%20a%20City%20That%20Doesn%E2%80%99t%20Flood_%20Turn%20it%20Into%20a%20Sponge%20City%20-%20JSTOR%20Daily.pdf
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