FACTS: As green infrastructure BMPs have become more common, published case study data show that green infrastructure is actually less expensive than conventional “gray infrastructure,” in terms of both initial capital costs and annual maintenance costs. The cost savings estimated by the USEPA of green infrastructure BMPs versus conventional gray stormwater BMPs ranges from 15 percent to 80 percent.
Savings result from reduced lifecycle costs, reduced up-front need for the installation/construction of expensive gray infrastructure (curbs, gutters, and large detention basins), and reduced land area requirements. At the same time, there are additional societal and economic benefits associated with green infrastructure BMPs. These include flood attenuation, fewer “nuisance” flood events, added site aesthetics, higher property values, and passive recreation. Due to runoff being managed closer to its point of generation, a reduction in the use of deicers for roads and walkways is another often-cited benefit. And, green infrastructure BMPs such as green roofs have been shown to translate into lower energy bills due to better building insulation and urban heat sink mitigation.
FACTS: Not so. Maintenance requirements of some green infrastructure BMPs are really not that different than old-school stormwater systems like detention basins. NJDEP requires all stormwater BMPs be inspected quarterly and after all storm events generating more than an inch of rainfall; this applies to conventional detention basins as well as green infrastructure BMPs. The routine maintenance of all BMPs also includes the periodic removal of debris from inlets and outlets, weeding of invasive species, replanting of bare areas and the occasional removal of accumulated sediment. Whereas conventional grassed detention basins need to be mowed weekly, bioretention basins, rain gardens, and vegetated swales need only be mowed once per year.
Some green infrastructure BMPs require specialized maintenance. For example, permeable pavement should be swept and vacuumed periodically, and green roofs need to be maintained by trained personnel.
For the majority of green infrastructure BMPs, routine maintenance activities can be implemented by landscape contractors and public works staff. Care does need to be taken, however, to avoid compacting the underlying soils. The porosity and uncompacted nature of the soils used to construct green infrastructure BMPs are key to their long-term performance. As with any infrastructure, it is important to have an Operation and Maintenance Manual consisting of maintenance instructions and a recommended maintenance schedule. This ensures that maintenance is conducted in a timely manner and is done correctly.
FACTS: Just the opposite. Green infrastructure has been implemented and tested throughout North America, South America and Europe. It has been shown repeatedly to be dependable and highly effective in various settings and climates. Green infrastructure BMPs are utilized extensively in large cities such as Philadelphia, Milwaukee, New York, Washington, D.C., and Seattle, as well as in smaller cities and towns such as Syracuse, Nashville, Lancaster, Austin and Chattanooga. In many large, older cities, green infrastructure BMPs are used to combat combined sewer overflow (CSO) problems. These cities rely on green infrastructure BMPs to reduce the off-site volume of runoff, thus decreasing how much runoff enters the storm sewer collection system. This in turn decreases the occurrence of CSOs.
Data compiled through various studies conducted in the U.S. and Canada show that green infrastructure is able to capture more than 90 percent of the runoff generated annually by storm events. For the more frequently occurring storms (up to and including rain fall events of 1.25 inches per two hours, which is New Jersey’s “water quality design storm”), this often results in no runoff being released from the site. Additionally, due to the combined treatment ability of vegetation and soils, total suspended solid loads are reduced by at least 90 percent and other pollutants transported by runoff, including nutrients, petroleum hydrocarbons and heavy metals, are significantly reduced as compared to standard gray infrastructure BMPs.
FACTS: Green infrastructure BMPs are routinely utilized with a high rate of success and effectiveness even in cold-weather climates. Studies at the Sustainable Technology Evaluation Program at the University of Calgary have shown that all types of permeable paving perform well in winter. And there is no evidence of increased damage due to frost heaving for permeable pavement as compared with regular pavement, because there is no standing water and associated freeze-thaw cycle, something that also cuts down on slip/trip injuries. Similarly, data compiled by the University of New Hampshire Stormwater Center demonstrate the utility and functionality of various green infrastructure BMPs under cold climate conditions, and there are numerous studies available through the USEPA demonstrating the functionality of green infrastructure BMPs in cold climate settings. The majority of these studies demonstrate that even though the plants may be dormant, there is still some degree of filtering and settling attributable to the remaining residual plant material. Thus, although the plants may not be actively assimilating nutrients and attenuating other pollutants, removal of settleable solids and suspended sediments still occurs.
Properly designed and constructed green infrastructure BMPs are capable of managing large storm events. Climate change-induced increases in storm intensity and runoff volumes do not pose a challenge to the implementation of green infrastructure BMPs. In fact, as compared to conventional stormwater management techniques, green infrastructure can greatly reduce the volume of runoff generated from large storm events. Capturing and infiltrating the first inch of rainfall helps delay peak flows during extreme events, allowing stormwater infrastructure to work more effectively. Numerous studies have documented that green infrastructure reduces average losses from flood events, even in areas with low-infiltration soils and higher flood risk. This often translates to flood control cost savings and performance benefits. As illustrated in Hoboken, when implemented on a community-wide scale green infrastructure BMPs help make cities more resilient to extreme storm events.
FACTS: This is one of the greatest fallacies concerning green infrastructure BMPs. In fact, green infrastructure BMP design standards for bioretention and infiltration basins specifically require that standing water drain from green infrastructure BMPs within 72 hours. This keeps mosquitoes from breeding. Additionally, the complexity of plants used in green infrastructure BMPs attracts and supports beneficial organisms that feed on mosquito larvae. A properly maintained green infrastructure BMP will not breed mosquitoes or attract pests.
In the case of constructed wetlands or wet ponds, mosquito control is easily achieved through biological means such as Bti, which is harmless to birds, amphibians, pollinators and other beneficial organisms. These BMPs also provide habitat for dragonflies, nature’s most voracious mosquito predator. The presence of dragonflies can help reduce mosquito populations in entire neighborhoods.
Myth Busted: There are numerous monetary, regulatory, aesthetic, and flood-control benefits to implementing green infrastructure BMPs as opposed to conventional gray infrastructure techniques. One of the biggest incentives is that decentralized stormwater management systems often free up more land than the traditional large-basin stormwater management methods. Also, due to the performance characteristics of green infrastructure BMPs, developers can satisfy the post-development stormwater management requirements of local ordinances and the state’s stormwater regulations more readily. Also, as previously noted, the aesthetic and passive recreational attributes of many green infrastructure BMPs can increase property values and community attractiveness. Finally, the long-term maintenance costs of green infrastructure BMPs are no greater, and in most cases are actually less, than conventional gray stormwater management practices.
FACTS: Green infrastructure stormwater best management practices (BMPs) can be implemented in rural or urban settings, as part of new land development projects or as part of site redevelopment projects. However, green infrastructure BMPs have proven to be especially effective in correcting stormwater problems (rate, quality, volume and recharge) in urban settings. Thus, green infrastructure BMPs are often associated with urban sites, especially urban redevelopment projects.
In general, green infrastructure stormwater management techniques can be thought of as de-centralized BMPs that rely on capturing and managing runoff close to its point of generation. This is in contrast to conventional stormwater management techniques designed to collect and channel runoff to large basins.
Therefore, although some of the best-known examples of green infrastructure BMP implementation involve retrofits and the integration of green infrastructure BMPs into existing conventional stormwater collection systems (Philadelphia, Portland, Milwaukee and Seattle), green infrastructure BMPs are especially well suited for implementation as part of new developments. Green infrastructure BMPs may satisfy NJDEP’s water quantity, water quality and groundwater recharge standards if an installation is designed in accordance with NJDEP’s BMP manual. New Jersey Future’s New Jersey Developers’ Green Infrastructure Guide provides examples of green infrastructure BMP applications for small-lot and large-lot developments for both new-development and redevelopment scenarios.