Site and Stormwater ManagementExisting Commercial
What is Site and Stormwater Management?
Site and stormwater management includes techniques for handling stormwater to avoid runoff, erosion, flooding and other harmful effects of uncontrolled water discharge as well as other site protection and resource conservation practices. Stormwater runoff occurs when precipitation, in all forms, falls on land or impervious surfaces and does not infiltrate into the ground. When the runoff flows over the land or impermeable surfaces, including paved surfaces and building rooftops, it combines with pollutants such as debris, chemicals, and sediments. This polluted stormwater can negatively affect the hydrology and water quality of local water sources, resulting in habitat modification and loss, increased flooding, decreased biological diversity, increased sedimentation and erosion, contaminated drinking water, and forced beach closings due to health threats to swimmers.
Site and stormwater management includes both Low Impact Development (also known as nonstructural strategies) and Green Infrastructure. Low Impact Development is the concept of designing a site to reduce the negative environmental impacts. Design techniques include
- Preserving stream buffers
- Minimizing the number of trees cut down during construction
- Reducing the use of heavy equipment
- Selecting soils and vegetation beneficial to the site
- Utilizing green infrastructure practices that treat stormwater through soil and vegetation
The NJ Department of Environmental Protection’s Stormwater Best Management Practices Manual provides guidance on Low Impact Development strategies for new and existing projects in New Jersey.
Green Infrastructure refers to stormwater management practices that capture, filter, absorb, and reuse stormwater, restoring the natural water cycle, reducing stormwater runoff, promoting infiltration, and enhancing evapotranspiration. For example, green infrastructure can effectively turn parking lot islands, street medians, tree planter boxes, and landscaped areas near buildings into specialized stormwater treatment systems. Developers and property owners can redesign parking lots to reduce impervious coverage and increase stormwater infiltration. Innovative site and stormwater management designs may also include vegetated or green roofs, methods for capturing and reusing rainwater, and the use of pervious paving materials in low traffic areas, parking areas, and walking paths.
The NJ DEP’s Green Infrastructure for New Jersey website provides informational fact sheets on common green infrastructure practices, including rain gardens/bioretention basins, grass swales, constructed gravel wetlands, and rain barrels. The Rutgers NJ Agricultural Experiment Station – Water Resources Program – Green Infrastructure Guidance Manual for New Jersey provides detailed information for the identification, design, and implementation of green infrastructure practices throughout New Jersey.
How to Integrate Site and Stormwater Management
Both LEED v4.1 Operations & Maintenance (O+M), and SITES require stormwater management as part of their certification systems. Under Sustainable Sites, LEED O+M awards points for rainwater and site management strategies. SITES offers a comprehensive, performance-based rating system for sustainable landscapes. SITES certification applies to new construction projects as well as existing sites that include significant renovations (with or without buildings). Projects constructed within the last two years with a minimum of 2,000 square feet qualify for certification.
Existing commercial projects that impact the site should have a site protection plan included in the contract documents. A site protection plan protects the natural resources of a project site and adjacent areas and achieves compliance with local laws and codes. Existing trees and vegetation, healthy soils and natural hydrologic systems on a site are all valuable resources to consider protecting before a construction project begins.
The sections below focus on the redesign of landscaping and incorporation of pervious paving materials, rain gardens, and vegetated roofs as ways to reduce a current commercial building’s stormwater runoff and incorporate best management practices for site development.
Native and Adapted Plants
Consider incorporating a native NJ habitat with plants adapted for the site. A native plant species thrive naturally in a particular region, ecosystem or habitat without direct or indirect human actions. Adapted plants have evolved to the physical conditions such as soil, climate, and geology of a site but were not formally part of the natural ecosystem. Invasive plants grow quickly and aggressively, often displacing native plants and adversely impacting native wildlife, local food sources, and pollination.
Landscaping with plants that are native and adapted to the Mid-Atlantic geographic region nurtures a diverse and healthy ecosystem and saves time and money on maintenance. Diverse native habitats resist disease and reduce the need for synthetic pesticides, increase biodiversity and provide habitat for native wildlife, reduce stormwater runoff and mitigate flooding, and provide an alternative to the time-consuming, energy-intensive, and water-inefficient practices of lawn and turf care.
The Native Plant Society of New Jersey provides a list of NJ native plants by County.
Pervious Hardscape Materials
Pervious paving systems absorb water rather than diverting water into underlying soils, reducing runoff and treating pollutants as water passes through soils and replenishes groundwater. Pervious surfaces include pervious concrete, porous asphalt, interlocking concrete pavers, and grid pavers. Review municipal regulations for permission to use pervious paving materials and consult with local officials and Soil Conservation Districts.
Using pervious hardscape materials reduces:
- Decrease the rate and quantity of stormwater runoff
- Reduces pollution of total suspended solids and nutrients in the soil
- Eliminates the need for or reduces the size of detention ponds, protecting open space and wildlife habitats
Three types of pervious pavement systems include pervious concrete, porous asphalt, and interlocking concrete pavers. Proper installation and base materials such as open-grade crushed stone maximize the surface’s ability to absorb and store water.
Maintenance and Tips:
- Consider using salvaged bricks or recycled stone pavers
- Look for a regionally-quarried stone to reduce transportation costs
- Prevent clogging by cleaning any soil deposited on pavement and vacuum (as necessary) twice each year
- Maintain planted areas adjacent to the pavement
Rain Barrels and Cisterns
Rain barrel and cistern systems collect, store, and distribute water for later use, providing a cost-effective and environmentally beneficial way to conserve water and minimize problems associated with stormwater runoff. Use rainwater collected in barrels and cisterns from catchment areas such as rooftops for irrigation, flushing toilets and other non-potable uses. Treat or filter the water depending on the intended use. Commercial applications often use cisterns or large-scale rain barrels.
Standard components of a rain harvesting system include
- Catchment area such as a roof
- Gutters and downspouts
- Leaf screens
- Rain barrel or cistern for storage
- Conveyance system to deliver stored water via gravity or pump
- Water treatment or filter system
Set aside sufficient space, either interior, above ground or underground, for the appropriately sized barrel or cistern. The size of rain barrels and cisterns varies from as small as 55-gallons to systems that hold thousands of gallons )which may require the use of an electric pump for distribution). To calculate the volume of water available for capture, assume that every 1,000 square feet of catchment area generates 600 gallons of runoff during a one-inch rainfall event.
Catchment Area * Inches of Rain * 600 gallons *0 .75
1,000 square feet
Consider combining rain barrels and cisterns with a drip irrigation system to direct overflow to a dry well, rain garden or bio-retention area.
Rain barrels require maintenance. Use water within two weeks to prevent algae growth and clean barrels every few months. A screen with a cover prevents algae growth and mosquito breeding. Drain, disconnect and store rain barrels during the winter months.
For more detailed information about the design and construction of rain barrels and cisterns see the Rutgers Water Resources Program’s – Green Infrastructure Manual for New Jersey.
Rain gardens, also referred to as vegetated swales and bioswales, consist of sloped depressions in the landscape planted densely with native plants that can soak up and filter stormwater runoff from rooftops, streets, or parking lots. Rain garden vegetation absorbs and filters stormwater before it enters storm drains.
Place rain gardens to capture runoff from a site effectively. Observe the site during the next rain and note where runoff problems exist. Consider the following:
- Does it come from a roof or downspout?
- Is there runoff from a parking lot?
- Does the runoff gravitate towards one place more than another?
As a general rule of thumb, place the rain gardens at least 10 feet from building foundations if the structure has a basement; for buildings without basements, place rain gardens at least 2 feet from buildings.
The Rutgers NJ Agricultural Experiment Station’s Water Resources Program has installed over 125 demonstration rain gardens in New Jersey.
For step-by-step guidance on installing a rain garden, see The Rutgers Water Resources Program and the Native Plant Society of New Jersey’s Rain Garden Manual of New Jersey.
A vegetated roof or green roof consists of vegetation in a lightweight growing medium placed on top of the drainage layer, root barrier, and waterproof membrane (see Figure 1). Vegetated roofs provide many environmental benefits such as decreased stormwater runoff and reduced energy use. They absorb air pollutants and provide a habitat for beneficial insects and birds, serve as a sound barrier, and mitigate the urban heat island effect. Use a pre-engineered green roof system or customize the green roof to achieve a project’s specific performance objectives. Vegetated roofs often weigh between 10-50 pounds per square foot. Consult a structural engineer and evaluate the strength of the roof before installing a vegetated roof on a building. Consider reinforcing the roof to support the added weight.
The two primary categories of vegetated roofs include: extensive and intensive. Extensive vegetated roofs consist of lightweight systems with shallow soil (or other growing media) depths usually less than 6 inches. Extensive vegetated roofs require less structural support than an intensive system and support a limited palette of hardy plants adapted to extreme environments that need little maintenance. Intensive vegetated roofs have deeper soil typically have more than 6″ of soil or other growing media, weigh more than extensive vegetated roofs, and can support a greater variety of plants. Intensive systems require more maintenance and a higher initial investment than an extensive roof.
Vegetated roofs can host a variety of plant species but typically include drought-tolerant species such as hardy succulents, sedums, and perennials. Consider low-maintenance, native species capable of living in the shallow soil. For a list of species indigenous to the Northeast, see NYC Greenbelt Native Plant Center or List of NJ Native Plants by County.
Vegetated roof requires some maintenance such as watering during the establishment period and occasional weeding. Seasonal pruning and cutting of grasses and annual plants reduce the accumulation of combustible material on the roof. Regularly inspect and maintain the components of the roof’s drainage system such as gutters, underdrains, and downspouts.
Blue roofs are systems designed to store and slowly release stormwater. Orifices, weirs, or other outlet devices manage and control the discharge rate of rooftop runoff, thereby reducing the size of downstream detention basins. Locations where the roof makes up a majority of the impervious surface area of the site, and where there is little room at the site for other stormwater management strategies make blue roofs most effective.
For more information on blue roofs, see the NJ Stormwater Best Management Practices Manual – Chapter 9.8 Blue Roofs.
Design landscapes that rely on natural rainfall and only require supplemental irrigation during the plants’ initial establishment period. Use native and appropriate non-native vegetation adapted to site conditions and climate. Group plants with similar water requirements to maximize irrigation efficiency and use climate-based controllers for irrigation systems to lower water consumption. Collect non-potable water for irrigation from sources such as rooftops, greywater, air conditioner condensate, or stormwater basins.
For more information, refer to US EPA’s WaterSense Water-Smart Landscaping Design Guide.
Example of Site and Stormwater Management
A one-acre park designed with green infrastructure such as bioswales, rain gardens, permeable pavement, and underground chambers that can store 200,000 gallons of stormwater runoff, South Park in Hoboken NJ helps reduce localized flooding in the surrounding neighborhood.
Effective stormwater management can;
- Alleviate the rate and quantity of stormwater runoff, thus mitigates flooding.
- Protect wetlands and aquatic ecosystems
- Improve quality of receiving waterbodies
- Conserve water resources
- Protect public health
Natural areas lost to development and replaced with impervious surfaces require new and costly levees, pipes, and pollution-control technology to perform displaced ecosystem functions.
The cost of site and stormwater management systems varies depending on the type of landscape and selection of strategies. For example, rain gardens vary in cost depending on the size of the roof and the selection of plants. According to the US EPA, estimated costs of installing a green roof average $10/sf for extensive roofing, and $25/sf for intensive roofs. Maintenance costs vary for either type of roof and may range from $0.75–$1.50/sf. The typical cost for institutional rain gardens ranges from $30-$40 per square foot depending on existing soil conditions, the selection of plants, and whether or not the project requires professional installation, organizes volunteers, or uses in-house personnel.
Green infrastructure integrates resilient and green design to complement and reduce reliance on traditional “grey” infrastructure.
In coastal areas, tidal estuaries and along rivers, native and adapted plants act as an essential buffer to encroaching water during flood periods while acting as a routine defense against beach erosion. For example, American Beachgrass considered one of the best lines of shoreline defense against storms and may also help prevent increasing levels of brackish water from infiltrating water tables close to a salt-water body. In general, the root systems of native plants can reduce runoff and mitigate flooding. In the event of droughts, water-efficient landscapes designed with native and adapted plants add layers of protection against water scarcity. Rain gardens designed with native and adapted plants support ecological resilience by increasing the biological diversity of plants and animals in a given area, which in turn, enhances the ability of the natural system to rebound after a disturbance.
When massive storms, hurricanes, or droughts cause municipal water sources to shut down or pollute wells, rain barrels and cisterns can provide stockpiled water. Filter and purify before using the water to irrigate edible gardens, wash dishes, and or provide water for drinking and showering.
Vegetated roofs can provide thermal insulation throughout all four seasons, reducing energy consumption and reliance on the electrical grid. In the event of a power outage, they can help keep temperatures cool in hot weather and warmer during the heating season. During heavy rainfalls and flooding events, vegetated roofs can help reduce stress on municipal stormwater infrastructure and reduce combined sewer overflows. Vegetated roofs can also offer local communities the opportunity to grow some of their food, reducing dependency on supply chains and transportation networks often disrupted or compromised from storms and other events.
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Rutgers NJ Agricultural Experiment Station – Water Resources Program