Impervious Surface

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Impervious Surface

What is Impervious Surface?

A surface that does not allow water to penetrate or pass through, such as concrete, asphalt, roofing, and other materials that prevent natural water infiltration into the ground, significantly impacting stormwater runoff and requiring careful management in site development and environmental planning.

Description

An impervious surface is a surface that does not allow water to penetrate or pass through, such as concrete, asphalt, roofing, and other materials that prevent natural water infiltration into the ground, significantly impacting stormwater runoff and requiring careful management in site development and environmental planning. These surfaces fundamentally alter the natural hydrologic cycle by preventing rainwater from soaking into the soil, instead directing it as surface runoff that can cause flooding, erosion, and water quality problems. Understanding and managing impervious surfaces is crucial for sustainable development and environmental protection.

The primary characteristics include complete or near-complete prevention of water infiltration, creation of surface runoff during precipitation events, alteration of natural drainage patterns, contribution to urban heat island effects, and impact on local and regional water cycles.

Common types include building rooftops and structures, paved roads and highways, parking lots and driveways, sidewalks and walkways, patios and decks, swimming pools and hardscaping, and compacted soils that have lost permeability.

FAQs

  • What is an impervious surface?

    An impervious surface is a surface that does not allow water to penetrate or pass through, such as concrete, asphalt, roofing, and other materials that prevent natural water infiltration into the ground.

  • What are examples of impervious surfaces?

    Examples include building rooftops, paved roads, parking lots, sidewalks, driveways, patios, swimming pools, and any surface that prevents water from soaking into the soil.

  • Why are impervious surfaces a concern?

    Impervious surfaces increase stormwater runoff, reduce groundwater recharge, contribute to flooding, cause water quality problems, and disrupt natural water cycles and ecosystems.

  • How do impervious surfaces affect stormwater?

    They prevent water from soaking into the ground, creating increased surface runoff that flows faster and in greater volumes, overwhelming drainage systems and causing flooding.

  • What are permeable alternatives?

    Alternatives include permeable concrete and asphalt, porous pavers, gravel surfaces, grass pavers, rain gardens, and natural landscaping that allows water infiltration.

  • Are there regulations for impervious surfaces?

    Yes, many jurisdictions have stormwater management ordinances that limit impervious surface coverage and require mitigation measures for new development.

  • How can impervious surface impacts be reduced?

    Impacts can be reduced through green infrastructure, permeable paving, rain gardens, green roofs, minimizing paved areas, and implementing effective stormwater management systems.

Fun Fact

Fun Fact: A single acre of impervious surface can generate over 27,000 gallons of runoff from just one inch of rainfall! Before urbanization, natural landscapes typically absorbed 90% of rainfall, but areas with 75-100% impervious surfaces can generate 55% runoff. The term “impervious” comes from Latin meaning “not allowing passage through.” Interestingly, even a 10% increase in impervious surfaces in a watershed can significantly impact stream health and aquatic ecosystems!

CSI Code

33 40 00

NAHB Code

1790