imperviousness

Imperviousness is the state or quality of being impervious, meaning resistant to penetration by liquids, gases, or other substances. In common usage, an impervious surface prevents water from soaking through. The term is used across disciplines, including materials science, civil engineering, and environmental planning, to describe how strongly a material or surface blocks infiltration or permeation.

In materials science and construction, imperviousness characterizes a material's barrier properties. Impervious materials—such as sealed concrete, coatings on metals, or impermeable membranes—oppose fluid passage. Real materials are rarely perfectly impervious; performance depends on factors like pressure, temperature, chemical exposure, joints, and wear. Designers often seek high imperviousness to moisture, chemical resistance, or gas barriers, while recognizing potential leakage paths at interfaces.

In hydrology and urban planning, imperviousness measures the extent to which a landscape surface prevents infiltration of rainfall. Impervious surfaces include roofs, roads, sidewalks, and compacted soil. Elevated imperviousness increases surface runoff, reduces groundwater recharge, and can contribute to flooding and water pollution. Urban designers deploy green infrastructure—permeable pavements, bioswales, rain gardens, green roofs—to lower effective imperviousness and promote infiltration and evapotranspiration.

Measurement and planning use imperviousness as a metric. It is expressed as a percentage of land area covered by impervious surfaces (for example, an urban parcel with 60% imperviousness). Data are derived from aerial imagery and GIS analysis. Imperviousness interacts with rainfall patterns, land use, and soil properties to shape stormwater management strategies and ecological outcomes.