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New paradigms for pavement stormwater management
Civil engineers must design to reduce runoff quantity, improve water quality, and ensure long service life for installed infrastructure.
By Bob Drake
Civil engineers’ primary concern in designing stormwater drainage for roadways and paved surfaces is to remove water from the pavement surface as quickly as possible. While that concern remains, dealing effectively with the quantity of stormwater is now complicated by heightened concern about its quality, and by efforts to retain more — or all — of the runoff onsite. In addition, this must all be accomplished with cost-effective methods and systems that promise extended service lives.
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At least two paradigm shifts are impacting the stormwater industry, according to Vaikko Allen, CPSWQ, LEED AP, regulatory manager, CONTECH Construction Products Inc. “The first is that onsite retention is being advocated as the most effective method of pollution control,” he said. “This is a shift away from percent removal-based regulation and toward consideration of pollutant loads. Other corollary benefits associated with onsite retention such as groundwater recharge reinforce this trend.
“The second shift,” said Allen, “is away from peak flow mitigation toward hydromodification control. The old way of matching the pre- and post-development peak flow rates for design storms — the two-, 10-, and 25-year storms — is not adequately protecting most streams where erosion occurs during storms as small as 10 percent of the two-year event. Some more progressive areas are moving toward flow duration control standards. The goal is to design systems so that pre-development erosion rates are not altered in the developed condition.”
Although a wide range of stormwater infiltration techniques can reduce runoff volume — such as porous pavements, rain gardens, small pockets of subsurface infiltration, and large underground infiltration bays — a common trend on roadway applications is to use a small-footprint stormwater treatment device, said Lisa Glennon, stormwater products manager for Hydro International. “Transportation authorities are typically working within very space-confined right-of-ways and, as such, engineers have to find space-efficient solutions for the treatment device during the design phase,” she said. “In the build stage, contractors need to install the equipment with as few road closures as possible.”
Carl Douglass, director of engineering for Prinsco, Inc., pointed out that both short-term construction costs and long-term maintenance costs are important to infrastructure owners, which requires additional focus on product performance and service life.
Other company representatives agree. “Designers are considering the lifecycle cost of a system to a greater extent than in past years,” said Kimberly Paggioli, P.E., vice president, Marketing & Quality Control for HOBAS Pipe USA. “The quality of the products is becoming a greater consideration, especially under roadways, where failures in underground utilities can adversely affect the streets above.”
According to Sarah Humphreys, marketing communications manager for JM Eagle, those failures are often caused by breakdown of the pipes used in stormwater management systems. “As the country rebuilds its broken infrastructure,” she said, “better technology and understanding of the life-span of the materials are accelerating the trend to make wiser choices in pipe products.”
Pipe and stormwater treatment devices also are susceptible to performance problems and shortened service lives when maintenance is inadequate. “If the pipe or stormwater management/treatment device is unable to be accessed to inspect or ultimately maintain, then there may be a lack of uncertainty as to whether that product or device is actually performing the action it was designed for,” said Brian Stahl, P.E., central regional manager at StormTrap. “If a product is unable to be maintained, then one can only assume that the product’s effectiveness over time is [decreasing].”
New products for new paradigms
The increased focus on water quality and stormwater management in highway projects and other land development — plus increasing emphasis on low-impact development (LID) and Leadership in Energy and Environmental Design (LEED) certification — has created a need for innovative solutions, according to Tori Durliat, director of marketing, Advanced Drainage Systems, Inc. (ADS). Factors influencing the use of stormwater management products include the region, particulate matter to be treated, oils, hydrocarbons, LID requirements, green building initiatives, and the sustainability of the project, she said.
Consequently, to address the wide range of factors, “all the tools available to the civil engineer should be readily available and utilized,” Durliat said. “There are many cases when LID is simply not adequate to meet the public need and maintain an environmentally sustainable site. Pipe and manufactured stormwater management and treatment devices can provide additional tools that allow environmentally friendly designs. The use of multiple techniques such as LID combined with manufactured devices can provide an opportunity to utilize a treatment train approach in less space and [with] less land disturbance.”
Pipe and stormwater treatment device manufacturers surveyed for this article offered the following information about new or upgraded products that can help address the challenges of managing stormwater from roadway and pavement surfaces.
ADS offers the capability to capture stormwater through its Nyloplast inlets, store the water in underground retention/detention with pipe systems or StormTech chambers, and clean the water with inlet protection, separators, and filters. ADS provides a number of online design tools at www.ads-pipe.com for its regular pipe and StormTech Chamber line and is developing additional tools to assist designers.
In 2009, CONTECH launched the UrbanGreen brand that includes products specifically designed to meet emerging LID requirements. The UrbanGreen BioFilter is a hybrid landscape planter and media filter system that can be integrated into streetscapes to benefit water quality. The company also enhanced its detention/retention product portfolio with ChamberMaxx, an HDPE arch infiltration system that is installed below grade over a permeable sub-base, and DuroMaxx, a pipe design that incorporates helical steel reinforcement into a smooth interior plastic pipe to give the strength and size benefits of concrete pipe with watertight joints and handling advantages of plastic pipe, according to CONTECH.
The company offers a Design Your Own Detention System calculator (www.contech-cpi.com/stormwater/resources/dyods/599) and is developing a Low Impact Development Site Planner to guide designers through the best management practices (BMP) suitability and feasibility screening process and provide preliminary size, capital cost, and long-term costs for CONTECH BMPs, as well as for a wide range of non-proprietary systems.
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HOBAS recently introduced a non-circular pipe product to the U.S. market that the company said is especially useful in rehabilitating odd-shaped existing lines such as storm sewers. The new product closely fits the existing shape, with only a slight decrease in cross sectional area, thereby maximizing the flow volume. HOBAS offers a flow calculator on its website (www.hobaspipe.com) to assist designers in determining the appropriate size pipe for various diameters and Manning’s n value combinations.
Hydro International just launched Stormbloc, a modular, crate-type stormwater infiltration block that is used for large infiltration bays or for small pockets of infiltration distributed around a drainage site. It incorporates access tunnels so maintenance crews can inspect and clean out the entire system from the surface. The company also recently offered a new model of its Reg-U-Flo Vortex Valve, a passive flow control that helps match post-development runoff rates to pre-development levels. The Reg-U-Flo Vortex Valve is typically used in culverts, catch basins, or natural depressions to constrict the rate of runoff leaving the site.
The company offers LID and LEED design guides on its website (www.hydro-international.biz) and recently launched an online Stormbloc sizing calculator. Engineers will find Hydro’s Reg-U-Flo Vortex Flow Controls in various modeling programs such as HydroCAD, PondPack v8i, and MIDUSS. Also, a Reg-U-Flo Design sizing program outputs a head/discharge flow characteristic that can be imported into most drainage system modeling software, the company said.
JM Eagle (www.jmeagle.com) recently launched Eagle Corr PE (Dual Wall), a corrugated HDPE pipe that features an integral heavy-duty bell and dual-gasket spigot for a 10.8-pound-per-square-inch watertight joint. According to the company, Eagle Corr PE (Dual Wall) offers the strength of the corrugated design with the maximum hydraulic efficiency of a smooth interior. A version of Eagle Corr PE with 50-percent recycled resin content will be available in summer 2010.
Prinsco (www.prinsco.com) developed ECOFLO pipe, a dual-wall, corrugated HDPE pipe that, according to the company, meets or exceeds the AASHTO requirements for virgin pipe and contains a minimum of 50 percent recycled content. Additionally, the company recently introduced its Integrity line of seamless HDPE fittings designed with increased structural and watertight integrity. The fittings are manufactured with a seamless core, resulting in significant performance improvements for watertight systems, the company said, especially in applications that receive increased loading from deep burial depths or vehicular traffic. Prinsco offers two software packages to assist civil engineers with calculations for underground detention and water quality treatment.
In 2008, StormChamber introduced SedimenTrap, which it said significantly increases the ability of the company’s StormChamber systems to also function as water quality devices. The cone-shaped HDPE devices are placed in the first and last chambers of a row receiving the stormwater inflow to enhance the system’s sediment retention and maintenance ability, eliminating the need for costly pre-treatment devices, according to Bob Maestro, president and CEO of StormChamber.
During the last three years, North Carolina State University, in conjunction with the North Carolina Department of Transportation and the U.S. Environmental Protection Agency, have been testing replacement of piped stormwater discharges on Kure Beach, N.C., with small StormChamber systems to reduce the number of beach closures caused by fecal coliform contamination. Sampling data demonstrated that the systems eliminated more than 95 percent of bacterial contamination compared with prior baseline conditions, Maestro said.
The StormChamber website (www.stormchambers.com) provides a design calculator to determine the number of chambers needed, as well as the size of the trench and amount of stone and filter fabric required.
StormTrap (www.stormtrap.com) introduced ways to integrate water quality devices into its systems without sacrificing accessibility and maintainability. In addition to providing a number of options through StormTrap’s fully customizable systems, the company said it is focusing on providing these solutions through recycled and locally harvested materials to provide a greener product to clients at no additional cost.
Installed cost is always important, but the new paradigms for stormwater management are even impacting that. “Environmental factors in the development of roadways and parking lots are beginning to play as big a roll in some areas as the costs,” said ADS’s Durliat. Runoff quantity and quality and system longevity are the new watchwords.
