Pervious Paving

PermeablePaversThe Green Learning Station is proud to be the highest tech parking lot in the Midwest. We are home to an experiment comparing six types of pavement, five of which let water flow through them.

How does pervious paving work?

Stormwater flows through spaces between the pavers, or through gaps in the concrete or asphalt, into a gravel bed below. Water fills empty space between the pieces of gravel when it rains. Over time, water sinks into the ground below and eventually into our ground water. Pervious pavement helps keep our rivers clean in two ways: It keeps stormwater out of the sewer, reducing combined sewer overflows. Pollution carried by rain sticks in the gravel bed instead of washing into our rivers and aquifers.

The Green Learning Station has the following types of pavement:
Permeable pavers
pavers_from_abovePermeable pavers are a lot like regular interlocking pavers except they have spacers on the sides or are installed in a pattern that maintains space between the pavers through which water can travel. There is no sand in the installation, just gravel. Typical installations include a gravel bed beneath the pavers so the water can hang out there until it has a chance to seep into the ground below it. The depth of the gravel bed depends on how quickly the soil on your property allows water to sink into it.


Reading Rock Tri-Paver

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Reading Rock Hydrastone


Reading Rock Eco-flow

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City Line Ceramic Paver with Lugs (not a test area)

Porous Asphalt

Porous asphalt is made with large, angular gravel and is not sealed, leaving space between the stuck-together gravel for water to travel down.

To learn more about porous asphalt, visit the National Asphalt Pavement Association.
pavement_from_abovePervious Concrete
The absence of sand in the concrete mix allows water to flow through the spaces between the angular gravel held together by Portland cement.

To learn more about Pervious Concrete, visit the National Ready Mixed Concrete Association.

What is so special about the Green Learning Station’s pavement?

The GLS site used to be a gas station so we figured there is a pretty good chance that there are chemicals and petroleum products lingering in the soils underground. We didn’t want to pass a bunch of water through contaminated soils on its way to our groundwater, so we decided to line all of our pervious paving gravel beds with plastic. We basically built gravel filled bathtubs beneath each paving test area. This is not normal for pervious paving, but it does let us collect information about how water is moving on the site that we would not otherwise be able to measure.

Sensors measuring temperature and water flow are embedded in our pervious paving. The data streaming from the sensors and our weather station show us the dynamics of a storm – how water moves through the site. The information we collect can be used to make improvements to the design of rainwater management systems, help government officials make informed policy decisions and encourage more people to install green stormwater controls. We are in the process of condensing some of that data for you to see. Learn more about the Green Learning Station’s monitoring efforts.

The Green Learning Station is home to seven different types of paving surfaces, six of which are being evaluated as part of a long-term experiment made possible by the Metropolitan Sewer District of Greater Cincinnati.