Green infrastructure is an approach to managing stormwater that is modeled on natural processes and systems. The NJDEP defines green infrastructure as a stormwater management measure that manages stormwater close to its source by:
- Treating stormwater runoff through infiltration into subsoil;
- Treating stormwater runoff through filtration by vegetation or soil; or
- Storing stormwater runoff for reuse.
Unlike conventional gray infrastructure, which carries rainwater away from where it falls through gutters, drains, and pipes, green infrastructure keeps most stormwater on site through infiltration and beneficial reuse. In urban and suburban areas, this helps restore the natural water cycle and provides many environmental benefits. Rain gardens, green roofs, pervious pavements, and other types of green infrastructure practices can save money, satisfy permitting requirements, and increase public acceptance of your development project.
Green infrastructure practices have been installed successfully throughout New Jersey and they have proven to be as effective as gray infrastructure at managing stormwater in many settings. They offer a cost-effective way for developers to meet regulatory requirements, provide aesthetic enhancements for communities, attract customers to retail centers, and reduce long-term building energy costs.
While general knowledge of grading and landscapes is important for all contractors, many construction teams lack the knowledge and experience to successfully build green infrastructure. Stormwater management designs are site-specific. Green infrastructure design can have even more specificity due to soil media and plants associated with the system. Not all contractors are prepared to construct such systems. Be sure to require a demonstration of existing green infrastructure work as well as references for those projects during the bid process. Mandatory Pre-Bid meetings can help the design team convey the complexity of the systems to contractors. A contractor associated with subconsultants specializing in green infrastructure should be seriously considered. For certain systems, such as green roofs, familiarity with construction processes may determine the success or failure of a project.
In addition to a contractor with experience, it is also important to select design professionals with green infrastructure portfolios and a high degree of detail in their work. Engineers and landscape architects may be hired as a team to ensure that green infrastructure functions on a vegetative and hydrologic level in addition to an aesthetic and programmatic one. The transition from the design phase to the construction phase of a project is key as the owner, design professionals, and contractors need to be coordinated and aligned on the project goals and expectations. Throughout the entire process, communication between the client, developer, engineer, landscape architect, architect, contractor, and owner is vital.
NJDEP’s Stormwater Best Management Practices (BMP) Manual offers thorough guidance on all facets of stormwater management planning, design, and compliance. In addition, Rutgers Cooperative Extension (RCE) has created the Rutgers Green Infrastructure Guidance Manual in which the different types and benefits of green infrastructure practices are described. The Rutgers manual can be found here: Green Infrastructure Guidance Manual. Other useful resources are available through Georgetown Climate Center, University of New Hampshire, the Center for Watershed Protection, the EPA, and NJDEP.
There are specific requirements for “engineered soil” used in all types of bioretention systems, including rain gardens. Engineered soil is not topsoil. For specific guidance about soil mix, soil bed requirements, and best practices for soil amendments such as compost, consult Chapter 9.1 “Bioretention Systems” of the NJDEP Stormwater BMP Manual.
The NJDEP released the rule change into the state register on March 2, 2020. A one-year implementation period allows municipalities, developers, engineers, contractors, and other affected parties to adopt these rules into their policies, practices, and in the case of municipalities, their ordinances. On March 2, 2021, the rules will be in full effect, and all new development will be required to meet the new stormwater standards.
In addition to incorporating NJDEP stormwater rule standards and requirements into local ordinances, municipalities have the option to impose higher standards on non-residential projects than those set forth in N.J.A.C. 7:8. For instance, some municipalities define a “major development” with a smaller area of disturbance than the NJDEP’s one-acre standard. Thus, a project that is exempt from NJDEP major development regulations may still be required to provide stormwater management. Check your local ordinances early in the design process in order to ensure compliance.
Yes. The LEED rating system offers up to four points toward certification for managing rainwater on site. Points are awarded based on the percentile of regional or local rainfall events that are managed using green infrastructure. For example, managing rainfall in the 80th percentile is worth one point, while the 95th percentile is worth four points. It is calculated using a comparative analysis of daily rainfall data.
The full text of the rules as adopted on March 2, 2020, along with a set of Frequently Asked Questions can be found on NJDEP’s website (njstormwater.org). The website also includes revised or new chapters of the BMP Manual (Chapters 5, 12 and 13) and a revised model ordinance (Appendix D) to provide detailed information about complying with the new green infrastructure requirement. All of these resources can be accessed through the online version of this Guide.
No. A common misconception about green infrastructure is that it requires significantly more maintenance than traditional gray infrastructure or traditional landscape maintenance. This is not the case. Maintenance tasks are usually routine and can be done by the property owner or traditional landscape maintenance crew. Additional education may be needed for landscape crews unfamiliar with green infrastructure systems. However, the tools, practices, and manpower required are unaffected.
All stormwater management systems, whether gray or green, are recommended to have regular maintenance after storm events to inspect for clogs, debris, sediment accumulation, etc. The main difference is that failure to keep up with regular maintenance of a vegetated green infrastructure system will have a more noticeable aesthetic impact than and underground gray system.
Maintenance varies depending on the type of green infrastructure practice. For example, recommended maintenance for pervious asphalt pavement involves biannual vacuuming to remove fine sediments. Less overall maintenance is required compared to regular asphalt due to superior snow melting characteristics.
Landscape practices need regular maintenance to remove debris, replace mulch, and maintain vegetation (weed removal, cutback of dead vegetation, etc.). Inspections for erosion and sediment accumulation, pH testing, and other specified maintenance tasks can be performed occasionally as needed.
Rain gardens can be planted to look naturalistic, like a meadow, or they can be maintained with a more formal garden appearance. The plants and landscape design that are chosen will determine the appearance. If you think your customers would prefer a garden-like aesthetic over a meadow, simply communicate this need to the landscape architect or engineer. Like any garden, regular maintenance will ensure that it does not become weedy and overgrown. Unlike gray infrastructure, these are living systems and failure to provide regular maintenance to the vegetation will have a noticeable aesthetic impact.
Mosquitoes are one of the most common concerns that citizens tend to raise about green infrastructure, but this concern is addressed by standard design requirements. Green infrastructure practices are designed to drain within 72 hours or less, which will prevent colonization of mosquitoes that take about 72 hours to develop into their adult stage. Rain barrels, which may contain standing water for longer, should be covered with a mosquito net or screen to prevent mosquitoes from laying their eggs. Owners of rain barrels may also use microbial insecticide (BTI) granules or “dunks,” an organic and highly effective way to prevent mosquitoes from multiplying.
Green infrastructure practices, especially those located next to streets or sidewalks, should be designed with plants that are salt tolerant. They are also designed with well-drained soil that helps flush salt through the soil more rapidly and reduce high concentrations that negatively affect plants. Thus, road salt rarely kills the plants, although it can cause stress and damage if used in large quantities. To reduce the potential for any damage, you can choose eco-friendly salt alternatives such as calcium chloride, which is safe for plants and pets, or you can reduce the amount of salt spread.
The key difference between conventional concrete and asphalt pavements compared to pervious pavements is that the smallest stone particles, or fines, are left out of the pervious pavement mixture. This leaves small voids that allow water to infiltrate through the pavement. However, these pore spaces do slightly reduce the durability of the pavement in comparison with conventional pavements. Therefore, pervious pavements should be used strategically in areas with low vehicular traffic like parking stalls in parking lots or pedestrian and bicycle pathways. With proper design, construction, and maintenance, pervious pavement works well for many years, including in winter weather. Black ice does not form on pervious asphalt, as any thawed water infiltrates; thus, pervious asphalt can help prevent slip and fall accidents. The admixtures and binders selected will have significant impact on the pavement’s effectiveness. Refer to the NJDOT specifications and National Ready Mixed Concrete Association for design guidance. Durability varies based upon the type of pervious pavement system selected. For grass pavers, gravel systems, resin-bonded aggregates and various other products, consult manufacturer guidelines for construction and maintenance procedures
Green roofs are still able to perform in cold weather, although not necessarily at the same level of effectiveness as during warm seasons. The soil in green roofs is porous and remains pervious when frozen. Consequently, rainfall as well as snow that melts during freeze-thaw cycles can still be stored, although the water will not be used by dormant plants.
Various resources exist to guide contractors, developers, and maintenance crews in maintaining green insfrastructure. The New Jersey Department of Environmental Protection provides sample maintenance plans for Best Management Practices outlined in this guide. Additional online resources include the Philadelphia Water Department’s “Green Stormwater Infrastructure Maintenance Manual, Version 2.0.” The manual provides descriptions of routine maintenance procedures, frequency of maintenance, and preventative maintenance.
The Environmental Protection Agency (EPA) provides maintenance guidance in a “Green Stormwater Operations and Maintenance Manual.” The guide demonstrates levels of maintenance service from “Excellent” to “Poor.” This system is useful for evaluating the performance of your maintenance team.
Geese can be both a nuisance and a destructive force on green infrastructure. Young vegetation is particularly attractive to geese. There are several methods for repelling geese that should be considered in the design process. The most natural and effective is the use of vegetative buffers. Buffers should include tall grasses around the perimeter of the green infrastructure feature.
Green infrastructure practices often are more cost-effective than traditional gray infrastructure. Integrating green infrastructure into development projects can reduce costs by decreasing the amount of underground drainage piping and structures needed to manage stormwater, which reduces construction costs. Green infrastructure can also reduce operations and maintenance costs associated with development properties. For example, a green roof can reduce heating and cooling costs for a building. Green roofs also last longer than conventional roofs, which reduces replacement costs. In some cities and municipalities, there are incentives for use of green infrastructure, such as expedited reviews, density bonuses, connection fee credits, and redevelopment area bonuses. Consult the jurisdiction where the development is located for options.
Green roof cost will depend on the type of roof and the amount of weight associated with the type of system designed. A new building can be designed to support this additional weight. For existing buildings, a structural engineer should be consulted to ensure the rooftop is able to support the additional load. In many cases, the lightweight materials used for green roof construction allow for a retrofit on an existing building.
If designed thoughtfully, green infrastructure should not affect your ability to meet building codes. In most cases, green infrastructure can be sited far enough away from the building to avoid any potential concerns about infiltrating near foundations, etc. In the case of green roofs, these are most commonly integrated as part of the overall building design, and any potential increase in structural loads is addressed through the normal design process. Before installing green infrastructure, it is always advisable to check municipal codes, design standards, and planning to determine potential impacts on the development process. There are different steps that can be taken to address issues that might arise as a result of regulations and codes. For more information, visit the US Environmental Protection Agency website.
Currently, green infrastructure practices do not usually qualify for abatements or tax savings. Tax abatements or tax savings vary from municipality to municipality as each city or town decides what will or will not qualify for tax abatement or tax savings. Contact your local municipality for information about abatements or other incentives.