Reducing Urban Flooding

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By William Moss

Urban green space contributes to a healthy ecosystem.
Urban green space contributes to a healthy ecosystem.

Many parts of the country have been hit with devastating floods recently, and in urban areas the problem can be especially severe. Urbanization itself — clearing trees, draining wetlands, and paving the ground — makes flooding worse. Most natural landscapes absorb rainwater and allow it to soak through the root zone into the water table and aquifers. But the vast expanse of asphalt, concrete, and compacted soils in urban areas forms an impermeable barrier, similar to naturally impermeable areas like the rocky canyons of the American Southwest, where storms often cause flooding. When water is repelled from the surface instead of being absorbed, even manmade drainage systems meant to handle water flow in urban areas can be overwhelmed, and flooding can occur.

Urban runoff not only floods homes and buildings, it also carries toxins directly to rivers, streams, and lakes. Air pollution particles, sewage, solvents, detergents, fuel spills, deicing salts, plastics, and other trash are washed into the natural environment. The combined effects of flooding and the dissemination of toxins make storm water runoff a critical issue.

Make Room for Another Garden

Gardeners in urban areas help to reduce runoff and improve drainage with every garden we plant. Water readily percolates through cultivated soil, and plants and soil naturally filter toxins. Of course, in-ground gardens have the capacity to absorb and hold a lot of water, but even container and rooftop gardens can help.

Use Permeable Materials

We can also take things a step further by using permeable surfaces wherever possible in our landscapes. Driveways, sidewalks, patios, parking lots, and pathways can be made from porous materials that are firm, but that still permit water to drain through. Plastic grid systems, block pavers, porous concrete, and porous asphalt are some of the materials used to increase permeability. They all have different specifications and uses, so be sure to contact a city inspector or reputable contractor before beginning any projects. The U.S. Green Building Council gives Leadership in Energy and Environmental Design (LEED) credits for permeable surfaces. Insist that any new construction include some LEED certifications.

A driveway can grow flowers, too. (Photo by Cathy Cromell)
A driveway can grow flowers, too. (Photo by Cathy Cromell)

Promoting More Green Space

At the community level, gardeners can also encourage municipalities to adopt LEED standards and to create parks, common areas, and other green spaces. In tough financial times, these beautification projects are often the first to be ridiculed. However, their potential to mitigate runoff has a tangible, economic benefit to all citizens.

On the national level, gardeners can get involved with environmental restoration efforts. Wooded bottomlands, river corridors, marshes, peat lands, and swamps act as nature's sponges. They absorb rainfall and slowly release it over time, providing a tremendous benefit for downstream towns and cities.

Whether planting a garden, building with porous materials, or restoring a natural habitat, gardeners can help mitigate the negative effects of our urban environments. The garden you plant to filter the air, lower the heat island effect, provide habitat for animals, and provide food for your family can also keep storm water out of your basement. And your permeable walkway and driveway can help reduce local flooding. Urban areas will never be natural, but if we take steps to make them function more like natural areas, it can make a difference.

For more info, visit the U.S. Green Building Council.

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