Looking to forests for urban water solutions

Looking to forests for urban water solutions

Shanghai rain
Where does all that urban rain go? A shot of Shanghai.

This story first appeared on Asking Nature, the Biomimicry Institute and Biomimicry Global Network blog.

Have you ever walked through an evergreen forest in the rain? There is a hush all around. The forest floor is spongy and soft beneath your feet, and the layers and textures all around you create a coziness, a feeling of being protected. As you take a deep breath of fresh, clean air, you know it’s raining big drops up above, but all you feel is a cool mist floating down through the canopy.

You can find expansive sections of this forest all around Puget Sound, Washington. For many people, it is a mental and spiritual health reservoir, a place that helps us reconnect and remember that we are nature. But it is also an ecosystem services powerhouse. It stores carbon, cleans the air and water, regulates temperatures and provides shelter and food for critters big and small.

Before urban development, this forest dominated Seattle’s landscape. Dotted with bogs and meadows, with wetlands proliferating along the rich edges between forest and water, the vast majority of the region was forest. And the system operated in dynamic balance.

The current gap between forest and urban water flows

Now, the forest mist is an unchecked rain that washes across polluted streets and sidewalks. The urban hardscape of Seattle and surrounding areas interrupts the balanced ecological flow of our predevelopment forests and wetlands. We know imbalance creates stress on a system, but how do we regain ecological equilibrium in areas that are now urban? What can we learn from nature that will help our cities thrive?

How can we design our buildings and infrastructure to function like the natural ecosystems that preceded them? The Urban Greenprint is a project that asks these questions, applying biomimicry at a city scale. The project looks at issues not only of water flows, but also of carbon flows and biodiversity.

Evaporation as a new approach to stormwater mitigation

The initial focus of the project is Seattle. Perhaps not surprisingly, the most eye-opening research to-date is related to rainfall. In the water-rich region of Puget Sound, the forest holds a critical role of helping regulate water flows. When we study these flows, we learn a very important fact:  when it rains on our region’s forests, 50 percent of that rainfall is evapotranspirated  used by the plants and then returned to the atmosphere.

For Seattle, as for many cities across the globe, polluted runoff is an enormous problem, and is considered by many to be our most critical environmental issue. The rainwater that washes across polluted roads and sidewalks flushes toxins into water bodies. What our research tells us is that if we can design our cities to evaporate half of the rainfall, as our local forests do, we will go a long way towards solving our polluted runoff problem.

Regulators and the building industry are putting forth tremendous effort to slow and filter water, but evaporation is rarely, if ever, emphasized. This is a primary component of our regional water cycle, and it needs to be addressed.

The current focus of the Urban Greenprint is to generate building design techniques and use of materials that take cues from our local natural ecosystems, including methods of construction that encourage evaporation.

Remember the mist you feel on your face when you walk through a coniferous forest in the rain? The layered and textured canopies of red cedars and other conifers break up big raindrops into fine droplets that readily evaporate. Tree trunks, lichen and moss hold onto moisture, as does the detritus on the forest floor and the rich organics in the soil itself. Textures, layers and permeability all contribute to a system that holds water like a sponge until it infiltrates or evaporates.

The Urban Greenprint is working with a diverse group of experts to determine how buildings and infrastructure can mimic these functions, researching materials and digging into questions such as:

  • What if rainwater, after being used inside a building, gravity-fed out to a spongy façade where it was held until it evaporated?
  • What if building skins had hydrophilic and hydrophobic surfaces, like moss, to hold onto water and slowly trickle it off the building, increasing the opportunity for evaporation?
  • What if curbs were built of material mimicking mushrooms to remediate stormwater and store it until it could evaporate?
  • What if downspouts coming off our buildings were designed to pool water in staggered trays along their height, allowing for evaporation, like the leaves of a tree?

The Urban Greenprint is exploring these and other ideas through community engagement and workshops with design and material experts in Seattle and the Bay Area, and they have put out a public call for any other innovative solutions. Contact them to share your ideas.

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