Runaway Runoff: The Problem of Urban Runoff
Runaway Runoff
Pavement, buildings and other waterproof surfaces cover a large portion of the land in urban areas like metropolitan Chicago. That means rain water cannot soak into the ground. Instead, it gushes into storm drains that discharge directly to local rivers and streams.
About 55 percent of rainwater that falls on a city runs off (and in intensely urbanized locations such as the Loop, runoff approaches 100 percent); only 15 percent of rainfall sinks in to recharge groundwater supplies. The remaining 30 percent evaporates back into the atmosphere.
For comparison, only 10 percent of rain that falls on natural ground cover (forests, wetlands or other natural areas) runs off, and about 50 percent soaks into the ground.
As rainwater runs over city surfaces, it picks up pollutants encountered along the way -- soil, oil and grease from cars, pesticides and fertilizers, pet waste and much more. Not only do such pollutants harm fish and wildlife, they also degrade drinking water supplies and often require that recreational waterways be closed.
What can you do?
If you plan to replace a walkway, driveway or patio in your yard this spring, consider using water-permeable surfaces such as wood decks, spaced bricks or concrete lattice instead of solid concrete or asphalt. These surfaces allow water to soak through to the ground, thereby reducing runoff from your property and helping to replenish groundwater supplies.