Every time it rains, the area that is rained on gets a shower. If the rain isn’t too heavy, rain is absorbed into lawns and green spaces, sinking down through layers of soil and rock and eventually joining the groundwater. The soil and rock act as a filter, screening out particles and absorbing pollution. But heavy rain, and rain that falls onto paved areas like roads and parking lots, washes over these surfaces, washing away dust, dirt, and more. This rain is directed into gutters and then storm sewers. Instead of being filtered through layers of soil and rock before it joins streams and rivers, it flows directly into our waterways.

What gets washed into storm sewers? Dust and dirt which is blown by the wind or tracked onto pavement by muddy feet or muddy tires, and also dangerous pollutants. These may include oil and radiator fluid from vehicle engines, detergents and cleaning compounds, salt and chemical road treatments, and illegally dumped wastewater from factories. Heavy rains that wash over lawns and green spaces before tumbling into gutters also wash away fertilizers and insecticides which were meant to stay on the lawn. These chemicals upset the ecology of our streams and rivers and are damaging to the animals and plants which live in and near them.

Concrete and asphalt are impermeable. They do not let water sink through them. That means that water washing over them goes directly into storm sewers and into streams. Permeable pavers, like those at the trailhead, do let water sink through them and are therefore better for the environment. They allow stormwater to be absorbed into the soil and filtered. Gravel paths and those covered in mulch are also permeable.