What are Permeable Surfaces?

- Have you ever noticed a puddle building up on the road after a heavy rain or maybe even a little stream flowing down along the road?

Sights like these happen because of impermeable surfaces.

This buildup of water contributes to a variety of problems, including flooding, runoff, pollution and erosion.

An impermeable surface is any solid surface that will not allow water to penetrate through.

Such as asphalt, concrete, stone, brick, roofing or extremely compacted ground like a soccer field.

An example of a commonly seen impermeable surface, a parking lot, is pictured here.

Extreme flooding situations happen because of too much impermeable surface cover in an area.

These impermeable surfaces are most common in urban and suburban areas.

As a result, runoff is a common problem here.

This graphic shows the difference between a natural landscape and an urbanized area.

As you increase the number of paved roads and buildings, you decrease the vegetation and therefore decrease the amount of water absorbed into the ground.

Water absorbing into the ground is called infiltration and it is much lower in urbanized areas.

The water has nowhere else to go but follow along the impermeable surface as runoff.

Stream health is directly related to impervious surface cover.

Water runoff gets superheated on dark surfaces, as well as collecting increased sediment deposits.

This runoff then flows into neighboring streams and waterways, which stresses or even kills wildlife.

As the percentage of nearby impervious surface increases, so does the impact on wildlife.

At five to 10%, sensitive species are absent and water may be slightly polluted.

When it gets to 20%, erosion is obvious and only mostly tolerant insects can remain.

Above 20%, and the habitat has become unstable for native fish and diverse wildlife.

There are a variety of ways you can reduce the effects of storm water on your property.

The first is to reduce the amount of impermeable surface cover on your property or mitigate impermeable surface impacts.

Some examples include rain barrels, rain gardens or green roofs.

Shown here is a large rain garden replacing traditional lawn practices, helping to greatly improve infiltration of storm water.

Another option to reduce storm water effects is to replace existing paving with permeable paving systems.

These are specially designed surfaces that replace asphalt and other traditional materials by utilizing pore gaps between the material that allows water to filter through into the ground.

You can see two common examples of permeable pavement here.

The picture on the left shows a form of permeable asphalt that can replace traditional sidewalks.

The picture on the right shows a contrast between permeable paving in the foreground and traditional pavement in the background.

These are permeable grid pavers that allow water to infiltrate through the gaps unlike traditional pavement.

There are a large variety of materials that qualify as permeable pavement, including porous asphalt, plastic grids, porous turf or permeable clay pavers.

In this picture, you can see a typical cross section of a permeable pavement structure and all of the layers it consists of.

A common layout includes a sand/gravel layer at the bottom, geotextile fabric barrier, underdrain if required, a storage reservoir and the permeable material on top.

This alternative greatly reduces the amount of runoff and therefore reducing the amount of chemicals being carried into the waterways.

Increasing the amount of permeable surfaces in urban planning can do wonders to help wildlife and local habitats thrive.

Next time you see water built up in the road, remember that this likely could have been avoided with permeable surfaces.