What’s the Difference? Pervious vs. Impervious Surfaces

A pervious surface allows water to percolate through to the area underneath rather than becoming runoff. Impervious surfaces are solid surfaces that prevent aeration, infiltration, and water penetration, resulting in a number of harmful side effects.

Why are Pervious Surfaces Important?

• Recharge groundwater resources. Water can reach and contribute to the water table for future use.
• Filter out pollutants in the water.
• Reduce contamination in surface waters like rivers, lakes, and the ocean. Water that runs into storm drains picks up pollutants that end up in our surface waters. Pervious surfaces limit the amount of runoff.
• Reduce the heat island effect. Places with large quantities of impermeable surfaces (urban cityscapes) are considerably hotter due to their heat-absorbing qualities. Therefore, they take more energy to cool down. Most pervious surfaces do not contribute to this problem.
• Reduce the chance of flooding. When it rains, a large amount of runoff caused by impervious surfaces can lead to flooding and erosion. Pervious surfaces absorb much of the water instead.

Examples of Pervious Surfaces

• Mulch, Lawns, Soil, Sand, Silt, Clay, etc. Naturally porous material that allows air and water to move through it.
• Pervious Concrete. Concrete with a high porosity that allows water to pass right through.
• Permeable Pavers. This type of surface has either concrete or stone pieces with open spaces in between to allow water to pass through.
• Porous Asphalt. Standard asphalt that allows water to drain through it.
• Pavers in a grid or lattice pattern. Placing pavers in a pattern with spaces in between for groundcover to grow.
• In some cases, recycled material can be used to optimize sustainability.
• For more information on pervious surfaces, please click here.

Examples of Impervious Surfaces

• Common Construction Materials: Asphalt, concrete, brick, and stone
• Roofing & Man-Made Buildings.
• Compacted Soils. Soil compacted through urban development, or routine human use can become impervious over time.