what is impervious area

2 min read 25-12-2024

Impervious areas are surfaces that don't allow water to penetrate the ground. Instead, water runs off these surfaces, impacting local hydrology and potentially causing flooding and pollution. Understanding what constitutes an impervious area is crucial for effective stormwater management.

Defining Impervious Surfaces

An impervious surface is any hard surface that prevents water from infiltrating into the soil. This includes a wide range of man-made features commonly found in urban and suburban landscapes. Think of it as anything that water can't soak into.

Examples of Impervious Areas:

Roads and Parking Lots: Asphalt and concrete are prime examples. These cover vast areas in developed regions.
Buildings and Roofs: The sheer size of buildings significantly contributes to overall impervious coverage.
Driveways and Sidewalks: These smaller surfaces collectively add up to a substantial impervious area.
Patios and Decks: Hard surfaces in residential areas also contribute to runoff.
Sports Fields (Artificial Turf): While some synthetic surfaces are designed for water penetration, many are effectively impervious.

The Impact of Impervious Surfaces on Stormwater

The presence of extensive impervious areas dramatically alters the natural water cycle. This leads to several significant consequences:

Increased Runoff: Water flows directly into storm drains and waterways instead of seeping into the ground. This increases the volume and speed of runoff.
Higher Flood Risk: Rapid runoff overwhelms drainage systems, leading to increased flooding in urban areas.
Water Quality Degradation: Runoff from impervious surfaces carries pollutants like oil, fertilizers, and litter directly into streams and rivers, impacting water quality.
Reduced Groundwater Recharge: Less water infiltrates the ground, reducing groundwater levels and potentially impacting wells and ecosystems that rely on groundwater.
Increased Erosion: Concentrated runoff can cause increased erosion in streams and rivers, damaging stream banks and habitats.

Managing Impervious Areas: Strategies for Mitigation

The negative impacts of impervious areas necessitate effective management strategies. These focus on minimizing the amount of impervious cover and managing the runoff generated.

Methods for Reducing Impervious Cover:

Green Infrastructure: Replacing some impervious surfaces with permeable pavements, rain gardens, green roofs, and bioswales helps manage runoff and improve water quality.
Smart Growth Planning: Careful urban planning can minimize sprawl and prioritize development in areas with less environmentally sensitive land.
Brownfield Redevelopment: Redeveloping existing developed areas rather than expanding into undeveloped land reduces the overall increase in impervious surfaces.
Permeable Paving: Using permeable materials for driveways, sidewalks, and parking lots allows water to infiltrate the ground.

Techniques for Managing Stormwater Runoff from Impervious Areas:

Stormwater Detention Basins: These constructed basins temporarily store runoff, allowing it to slowly infiltrate the ground or be treated before release.
Retention Ponds: Similar to detention basins, but they permanently store some water. They can also provide habitat for aquatic life.
Filter Strips: Planting vegetated areas along waterways can filter pollutants from runoff before it reaches the water bodies.

Conclusion: The Importance of Impervious Area Management

Impervious areas significantly impact local hydrology and water quality. Effective stormwater management strategies are crucial for mitigating these impacts and ensuring the health of our water resources. Understanding what constitutes an impervious area is the first step towards implementing effective solutions. By incorporating green infrastructure and employing smart growth planning, we can work towards creating more sustainable and resilient communities.