In the Pacific Northwest, the last decade has seen a dramatic evolution in pervious pavement systems as communities stare down the threat of polluted run-off affecting the region’s waterways. From Seattle’s first pervious concrete roadway in 2005, to the more frequent presence of porous systems in the public right of way and in private development, this multi-purpose infrastructure is helping to relieve a huge burden on our region's ecological health.
Care of these facilities is not only vital to their function and longevity, but with so many systems in place, and more coming online, it becomes vital to the health of the community and environment. These systems must be adequately maintained to provide both stormwater and mobility functions.
So what is the new normal for roadway maintenance when your pavement is porous? Traditional methods don't exactly do the trick, but that's not keeping the equipment suppliers from getting in on the game. A business opportunity is at hand, and fortunately these green pavement systems are benefiting from the maintenance sector's race to be first in line with the newest and best piece of cleaning equipment. Ten years ago, there were few companies advertising cleaning for pervious pavements. Agencies tried different techniques but there was little demand to clean the systems. Now you can barely throw a permeable paver without hitting a manufacturer willing to show off the newest innovation in porous pavement care! Well that's a bit of an exaggeration, but the developments have been pretty fantastic!
The 100-year-old Elgin Sweeper Company is participating in research programs in order to better understand the maintenance requirements of pervious pavement systems. Bunyan Springs, a company "dedicated to the continued advancement and development of pervious concrete technology" has in recent years developed the Bunyan Infiltration Restoration Device (BIRD) which combines a push-behind vacuum innovation with a conventional roadway vacuum truck. And Ben's Cleaner Sales Inc., Triverus and the Seattle Pump and Equipment Company demonstrated their push behind vacuum technology during a demonstration on the pervious concrete paths and parking area at Greenwood Park and Federal Way.
Typically these pavement systems, which include pervious concrete, porous asphalt, and a whole smattering of proprietary permeable pavers have design infiltration rates of hundreds, sometimes thousands of inches per hour (a recent market addition which bucks this trend is the KlorostoneTM ceramic paver with a design infiltration rate of 4in/hr.) A few years after placement, the infiltration rate of these systems will decrease significantly due to leaf litter debris or sediment build up. Several years after installation, and with no maintenance, the infiltration rate of Seattle's first pervious concrete roadway dropped from over 700in/hr down to 9in/hr. And while this seems dramatic, keep in mind that our heaviest rain events in the Seattle area shower us with 4 inches in a 24 hour period. With semi-annual maintenance, a properly designed porous pavement can be expected to retain sufficient drainage capacity and structural integrity to do the infrastructure heavy lifting it's designed to do.
Not only are we seeing development in the field of maintenance equipment but more and more we find answers to the questions of "what", "when" and "how" to care for these systems. The National Ready Mixed Association (NRMCA) Provides guidelines for pervious concrete maintenance in the "Pervious Concrete Pavement Maintenance and Operations Guide". From state and city, to project-level, agencies have developed their own guidance document including the City of Bellevue and SHA High Point. And even more exciting is the research underway that may take the guesswork out of scheduling maintenance crews. At the 2015 International Low Impact Development Conference in Houston Texas, ORISE postdoctoral Fellow Robert A. Brown presented results of an ongoing study that measures the infiltration reduction of the surface from beneath the pavement, a monitoring system that results in a truly needs based maintenance schedule.
As manufacturers, suppliers, research institutes, and courageous agencies continue to collect the data, innovate the equipment, and inform the community, we can expect adoption of these porous pavement systems to become commonplace. In our region, this is good news for the Puget Sound and good news for the community.
by Lolly Kunkler