Permeable Paving and Stormwater Management

As California moves into the heart of winter and experiences the increased rainfall that accompanies it, the importance of using a permeable solution for paved surfaces becomes increasingly apparent.

Traditional, impermeable surfaces⁠—such as concrete or asphalt⁠—have played a huge role in the decline of watershed integrity in urban and urbanizing areas.  These surfaces can affect water quality, affect streamflow, and even increase the likelihood of flooding by causing:

  • Higher discharges
  • More bank erosion
  • Increased sediment transportation
  • Increased pollutant loads to streams
  • Reduced groundwater recharge

Thankfully, alternative paving solutions exist that combat these issues.  Permeable pavement has a high porosity that allows rainfall to pass through it to the ground below, and comes with both environmental and financial benefits.

Benefits of Permeable Paving

Environmental benefits include:

  • Reduces storm water runoff rate and volume
  • Reduces water pollution by trapping pollutants in the pavement
  • Replenishes groundwater, which can in turn be used by plants surrounding the pavement
  • Reduces surface temperatures since permeable pavement doesn’t produce a “heat island”

Financial benefits include:

Additional Benefits

The benefits of permeable pavement are undeniable.  One study found that after one year’s use of four permeable pavement areas there was no measurable surface runoff from these areas. After returning to the site after an additional five years, all four permeable pavement systems showed no major signs of wear or clogging. Virtually all rainwater continued to infiltrate through every permeable pavement system, with little or no surface runoff.

Permeable Paving Options

A popular paving option is decomposed granite.  However, there are a few different types of decomposed granite solutions out there.  It’s important to know the differences between each, so one can choose the right option for the right environment.

Loose, decomposed granite is the least-expensive option, as it’s simply loose granite with no binders or additives.  While it has excellent drainage and the initial cost is low, loose granite can be costly to maintain since it’s affected by erosion and often needs to be filled in as it’s washed away or otherwise scattered from the initial installation site.  During wet periods, it is prone to becoming mushy and muddy, and can easily be tracked into homes, which may damage hardwood flooring.

Stabilized decomposed granite is comprised of a stabilizer mixed in with the granite aggregates.  There are a few different stabilizer options.

A stabilizer that is often used is a product made in India, called Psyllium husk Powder.  Once spread and compacted, it is similar in appearance to loose decomposed granite.  Over time, however, this product fails and replacing it can become costly since the stabilizer and the decomposed granite have to be mixed prior to being delivered to the installation site.

Another commonly used stabilizer is resin.  When mixed with decomposed granite, this stabilizer creates a firm surface that’s stronger than loose decomposed granite.  The primary downsides to decomposed granite stabilized with resin is that it discolors over time—meaning it lacks aesthetic appeal—and it is also not permeable.  The lack of permeability is a major issue, particularly if one is trying to meet the Provision C.3 requirements.  We will go into more depth about the Stormwater provision C.3 requirements in our February newsletter.

Decomposed granite can also be stabilized with a polymer base.  While this can be appealing to those looking for an option similar to loose decomposed granite, it fails in time allowing the decomposed granite to be tracked away from the installation location and into buildings.  The major downsides to this option is that it is not permeable, fails over time, has no color options, and has temperature requirements for installation that can delay or impact installation times.

This cross-section shows GraniteCrete™ on a lift of Class II permeable base rock.

Decomposed granite stabilized with GraniteCrete Admixture has the look and feel of a crushed organic surface, with multiple surface finish options: loose, smooth, and coarse. It requires little to no maintenance, does not fail over time, and has excellent erosion control.  It is also permeable, allowing water to easily pass through; since it does not contain any oils, resins, polymers, or enzymes, it will not cause water pollution.

GraniteCrete has been approved and accepted as a 100% permeable product by Monterey County.  As noted by the County in their determination: “This determination exceeds the minimum 40% pervious surface requirement established by Monterey County and has been confirmed by an independent testing laboratory. The important fact in determining GraniteCrete™ as a permeable surface is that the entire surface of the product infiltrates water. It provides 100% ‘pass through’ regardless of whether it is used as a 3″ lift for pedestrian traffic or a 4” lift for commercial and light vehicular applications.”

In many ways, GraniteCrete is the superior decomposed granite paving option.  Interested in learning more about how GraniteCrete™ can improve your next landscaping project?  Contact a representative.  We will be happy to answer any questions you may have.