As environmental regulations on how storm water runoff is handled tighten, property owners are increasingly becoming pressed to manage runoff in innovative ways – or face higher fees from cities and municipalities. Developers are charged by some local governments when stormwater runoff significantly increases the amount of water in storm sewer systems.
One way of reducing the need for storm water retention features – and thus reducing costs – is the use of new types of permeable pavement.
Federation Housing in Pennsylvania just completed a garden at a low-income housing building for the elderly that included 1,650 square feet of Porous Pave XL permeable pavement for the garden’s walkways and patio. The highly porous material – it has as much as 29% void space – is infiltrated with more storm water than permeable pavers and is made from 50% recycled rubber chips, according to Garrett Churchill Inc., the company that installed the pathways. The material is mixed onsite and then poured in place at a depth of 1.5 inches, atop a four-inch base of compacted crushed aggregate.
“The project required a paving material with more porosity than permeable pavers. Otherwise, we would have been required to install additional stormwater retention features at grade, adding costs and detracting from the garden,” said the director of operations for Federation Housing, Inc.
Another project – the Nature Discovery Center in Bellaire, Texas – also recently used Porous Pave XL to mitigate the effects of rainstorms that covered the old, impervious concrete pavers on the main path. Water passes through the pervious surface of Porous Pave at a rate of 5,800 – 6,300 gallons per hour per square foot, allowing stormwater to percolate down through the aggregate base below. The chief operating officer of the construction company that installed the pavers said the material was chosen for its infiltration performance, cost, appearance, and that fact that it is a “green” material.
Retail centers, too, are moving to porous asphalt for parking lots. When storm water is able to flow through the asphalt into a collection area below, it eventually replenishes the groundwater and, while it may cost more up front, it can lead to long-term savings. Another option is a pervious precast concrete, which also allows rainwater to flow through it to the groundwater below, according to Spancrete, a company that developed a pervious product called RePlenish.
Part of the reason for increasing local regulations is that many older cities, where sewage and runoff share the same underground pipes, are under federal decrees to cut back on – or in some cases eliminate – the amount of sewage flowing into local rivers and streams, according to Governing.com.
But city transportation engineers now have a new guide from the National Association of City Transportation Officials (NACTO) that may help them think of their streetscapes in new ways and potentially reduce negative impacts of storm water runoff. The guide offers ideas such as permeable pavements or rain gardens to help improve storm water infrastructure and management.
The topic of storm water management is a constant in certain areas of the country. In California, for example – now that the historic 5-year drought has ended – areas like Los Angeles County are once again exploring how to capture stormwater to protect against future droughts, according to the Redondo Beach Patch.