Written By: William G Handlos, P.E.
Does a porous pavement solution cost more?
Porous pavements are less expensive to install than impervious concrete or asphalt when you consider total project costs. When evaluating parking lot construction costs for porous pavements vs. impervious alternatives, you must consider the following cost “buckets.”
Traditional pavements such as bituminous asphalt or Portland cement concrete enjoy low cost and ubiquitous installation contractors. This information may lead one to think that choosing a porous pavement would lead to higher overall project costs, but that is a myth because almost everything else about traditional parking lot construction is far more expensive than the porous pavement alternative. Traditional hard-surface pavements require inlet structures, castings, and covers for inlets and manholes, underground pipes, outfall structures, and detention ponds.
Costs & Maintenance of Stormwater Ponds
Detention ponds have three major cost drivers. Land costs to locate a pond can vary wildly depending upon commercial real estate values, but it is not unusual for land to be upwards of $250,000/acre even in small markets. The impact of the land utilized for detention ponds does not end there.
Lost rental or income value is another cost consideration. Ponds take up valuable commercial or residential real estate, representing a continual annual and growing cost.
Finally, there is the detention pond construction cost and higher liability costs.
An additional consideration is safety and aesthetics. The word “pond” often calls to mind pleasant images of fish jumping and ducks paddling; however, ponds constructed for stormwater management purposes are rarely attractive from a safety perspective or aesthetics standpoint.
A retention pond retains water as it percolates into the soil below. Retention ponds pose a safety concern to children and can be especially dangerous in wet conditions because the slopes make it very difficult in rain and snow to escape once a child slides down the pitch.
It is difficult to mow close to the edge, and, as a result, tall grass and weeds end up collecting blowing trash. Fences placed for safety create garbage traps too. Additionally, the cyclone fence does not make for a very appealing aesthetic.
A detention pond’s primary purpose is to slow the water down from leaving the site, and these structures experience similar challenges. Both types of stormwater ponds are prone to collecting floating garbage and wildlife. This excess of organic matter causes sedimentation to build up at the bottom of the pond, reducing capacity and choking off infiltration.
A wealth of research proves that porous pavements contribute to an overall reduction in project cost and hazard mitigation while meeting aesthetic requirements. With porous pavements, stormwater detention is built right into the open-graded base course to a depth required for the site, so runoff is captured at the source.
The University of New Hampshire Stormwater Center put together a case study showing the economic advantage of porous pavements. The concepts in this case study are valid for a wide range of porous pavements, including modular pavers such as the GEOPAVE® Gravel Pavers and GEOBLOCK® Grass Pavers.
When comparing porous pavements to traditional pavements, make sure you consider all of the costs and safety implications that come with traditional pavements.
Choosing a green solution doesn’t have to cost more.
For more information on porous pavements, visit our web page: Porous Pavements.