Low Impact Development and Bioretention
By Mara Dias and Rick Wilson
Stormwater runoff is one of the greatest threats to water quality in this country. Contaminated runoff degrades coastal waters and habitats. Polluted stormwater is responsible for most of the beach closures and swimming advisories issued at our beaches across the nation.
As cities and towns expand and become more developed, large portions of our watersheds are being paved over with concrete and other impervious surfaces. These hard surfaces interrupt the normal water cycle by preventing rainwater from soaking into the ground. Rain instead runs across rooftops, parking lots and roadways picking up pollutants such as oil, fertilizers, and animal waste along the way. Marshes and wetlands are capable of cleaning many of the nutrients and pollutants in stormwater, but in many cases this natural vegetation has been lost as communities build out to the water's edge.
Stormwater is often channeled directly into streams, rivers and coastal waters through storm drain systems. Particularly problematic are combined sewer systems that exist in many of our older cities. Combined systems easily become overwhelmed and overflow raw sewage into receiving water bodies during storm events. While the consequences of stormwater runoff are most apparent in highly urbanized areas, it takes only a small increase in the percentage of impervious cover in a watershed for negative water quality impacts to occur.
Low Impact Development (LID) is a new approach to urban planning and site design that aims to maintain and restore the water cycle in developing watersheds. Sometimes coined “Green Infrastructure”, LID uses site-specific engineering designs that utilize Best Management Practices (BMPs) to infiltrate, filter, store and treat stormwater close to its source. LID construction and landscaping plans allow water to infiltrate into the ground, recharging local water supplies and protecting the water quality of nearby waterways. LID techniques are most effective when they are incorporated into the design for new development, but both commercial and residential properties can be retrofitted to hold more rainwater on-site.
There are many different types of BMPs that can be used to maintain a site's pre-development hydrology while still accommodating new development. The success of each is dependent on the specific conditions of a site such as soil type, topography, local precipitation and weather patterns.
Photographs of the successful installation of many of the following BMPs can be viewed in a power point presentation posted online by Orange County Coastkeeper and at the USDA Natural Resource Conservation District's online photo gallery.
Bioretention areas are vegetated depressions that collect and filter runoff. Bioretention BMPs increase the amount of rain water a property can absorb and include vegetative strips, grassy swales, rain gardens, shallow surface ponds, tree box filters and underground drainage systems. Bioretention areas are often advantageous to conventional stormwater techniques, such as retention ponds often installed in large development projects. They can often handle a larger amount of water and generally require less space than ponds, providing added economic incentives.
Rain gardens are a very popular bioretention BMP that are being incorporated into residential, municipal, and commercial property landscaping plans. Designed to hold and infiltrate rain water, rain gardens can also increase property values by adding to the aesthetic quality of the landscape. Native plant species that can tolerate standing water work best in rain gardens. Many cities are offering mini-grants to homeowners to install rain gardens on their properties. The City of Tallahassee, Florida is offering grants of up to $175 each to residents who plant a rain garden in their yard. Rain gardens also make great demonstration sites at schools and botanical gardens.
The Surfrider Foundation has put a coastal twist on rain gardens and is using its nationwide chapter network to implement an Ocean Friendly Gardens program that employs CPR (conservation, permeability and retention) techniques to protect the ocean and our beaches by reducing urban runoff.
The bioretention capabilities of a site can also be preserved during construction by saving and amending the topsoil. Often during construction the topsoil is scraped away, and the remaining soil becomes hard and compacted as large machinery and building materials weigh down on the ground. At the completion of the project, many builders roll out turf on top of the compacted soil, making it very difficult for subsequent rain to percolate into the ground. Saving and replacing the topsoil or amending the soil with organic matter can help retain the site's ability to absorb water and prevent runoff.
Permeable pavement is a LID application that is being used with great success across the country. Permeable pavement is an alternative to asphalt and concrete that allows rainwater to percolate into the ground. Most appropriate for lower traffic flow areas, permeable pavements have been used successfully to build parking lots, driveways, fire lanes, horse trails and bicycle paths. Although typically more expensive to construct than traditional asphalt pavement, their installation costs may be offset by a reduction in traditional curb and gutter systems. The benefits of permeable pavements include better infiltration, ground water recharge, reduction in runoff volume and treatment of stormwater for pollutants. One of the University of North Carolina's commuter parking lots was built with permeable pavement. This parking lot actually produces less stormwater runoff than a grass field! In contrast, traditional parking lots produce up to 16 times as much runoff as a grassy meadow of the same size. Here's another parking lot example from Melbourne, Florida.
Homeowners and local communities can see further reductions in stormwater runoff by employing alternative driveway and parking lot designs that reduce impervious surfaces and include bioretention strips or cells. Grass parking is also a good option for seasonal or temporary, event-related parking.
Green roofs are another innovative LID technique being employed to reduce runoff from the rooftops of both commercial buildings and private residences. Plants that can tolerate drought and extreme temperature conditions are planted in green roofs to absorb rainwater. Green roofs also help regulate the temperature of buildings and cut down on energy costs. The green roof on the American Society of Landscape Architects building in Washington, DC captures nearly 75% of total rainfall. An engineering analysis showed that the green roof's extra insulation lowered the building's energy usage by 10% in the winter, and up to 2-3% in the summer.
Roof rainwater collection systems are another BMP that can serve dual purposes. In arid areas, rainwater harvesting conserves water resources, while during wet weather, rainwater collection systems minimize the amount of stormwater running off rooftops. Particularly suited for retrofits, rain barrels and cisterns can easily be hooked up to homes and buildings. Channeling roof runoff to dry wells also keeps water out of the streets and storm drains.
Because Seattle has been struggling with frequent occurrence of combine sewer system overflows into Lake Washington, the Seattle Public Utilities is piloting a project to decrease the burden on the city's combined stormwater system by disconnecting residential roof downspouts from the storm drains and attaching them to rain barrels. They are also offering grant funding for the installation of residential rain gardens. With less water going into the system, they are hoping to see water quality improvements in Lake Washington as a result of fewer combined sewer system overflows.
Low Impact Development began as a concept that was promoted by NGOs and tested on university campuses. The success of LID techniques in controlling stormwater runoff is now being recognized by municipalities across the country, and we are beginning to see LID requirements incorporated into local code, ordinances, regulations and stormwater management plans.
In California, the Central Coast Regional Water Quality Control Board is requiring municipalities under the jurisdiction of their Municipal General Storm Water Permit to minimize negative impacts on aquatic ecosystems and degradation of water quality to the maximum extent practicable. Under this permit, cities are required to incorporate LID methodology into new and redevelopment ordinances and design standards, unless they are able to demonstrate that the cost of low impact development practices would be prohibitive and exceed any resulting water quality benefits.
Ventura is one city that is affected by the Central Coast Water Board's ruling. The Ventura Chapter of the Surfrider Foundation is taking advantage of this opportunity by promoting Ocean Friendly Gardens in Ventura and proposing LID applications to solve specific water quality problems that are affecting the beaches in Pierpont Bay, including Surfer's Point. View their recommendations in the Chapter's online report.
The Washington Pollution Control Hearings Board recently ordered the State's largest local governments to begin using LID techniques to control stormwater ‘where feasible'. This decision affects stormwater permits for the Cities of Seattle and Tacoma, and Clark, King, Pierce, and Snohomish Counties. It isn't certain yet how this decision will be applied to individual sites and projects, but you can learn more about the ruling here.
In the Metro Bay Region in Rhode Island an Urban Coastal Greenway has been designated around the northern reaches of Narragansett Bay. Within this highly urbanized waterfront, all proposals for new development and redevelopment projects must manage 100% of stormwater on-site and maintain 15 % vegetative cover. Applicants must incorporate LID techniques to the maximum extent practicable to meet the stormwater containment requirement.
Portland, Oregon has been a leader in promoting LID and green building practices through regulations and financial incentives. The city's code requires on-site stormwater management for new and redevelopment projects, and new city-owned buildings are required to install green roofs on at least 70% of the total roof area. The city also offers zoning incentives for privately owned buildings to install green roofs and will allow up to a 35% discount in stormwater utilities for properties with on-site stormwater management. Portland also has a progressive green streets program to meet many different community health objectives including stormwater management.
New Jersey and Maryland have both taken action on the state level to codify stormwater management rules. In 2004, New Jersey passed new stormwater rules requiring that sites maintain 100% of the average pre-construction groundwater recharge or allow for any increase in stormwater runoff to be infiltrated. The Maryland Stormwater Act of 2007 identifies LID practices as the preferred stormwater control method in the State and stipulates their use as the first control option for new development projects.
Given the growing acknowledgement of the benefits of LID, there is opportunity for Surfrider members and activists to push local governments to include LID strategies in stormwater management plans and community planning and zoning codes. Many smaller cities are now developing stormwater management plans to meet Phase II NPDES permit requirements of the Clean Water Act, and the public is invited to participate in these planning processes. Local planning and zoning boards and environmental commissions hold public hearings before approval of development projects. These hearings give the public the opportunity to ask for LID alternatives to be considered during the review of building permit applications.
The Center for Watershed Protection has posted several online Better Site Design publications. Another great resource which outlines how citizens can become involved in local rulemaking and planning to implement solutions to stormwater pollution in their community is the American River's Local Water Policy Innovation; A Road Map for Community Based Stormwater Solutions. Growth and development can move forward in ways that do not disturb the water cycle we depend on for clean water and beaches.
Also see the article Low Impact Development that appeared in the September 2007 issue of Surfrider Foundation's publication Making Waves.
Following is an index of Low Impact Development online resources.
LID Reference Websites
Low Impact Development Videos (USEPA)
Low Impact Development "Barrier Busters" Fact Sheet Series (EPA). These fact sheets explain the benefits of LID in clear terms and through examples. Specific fact sheets in this series directly address specific concerns that have been raised about adopting LID, thereby busting barriers.
USEPA National Pollution Discharge Elimination System. Green Infrastructure Webpage. LID techniques, fact sheets, case studies, regulations
Low Impact Development (LID) Center Urban Design Tools Website. Bioretention, green roofs, permeable pavement, rain barrels and cisterns, soil amendments, tree box filters.
Low Impact Development Center. General Information, techniques, handbooks & manuals.
Natural Resources Defense Council. LID definitions, benefits, case studies
West Coast. West Coast LID Portal - intended to serve as a community clearinghouse, providing information on funding sources, incentive programs, training opportunities, and technical resources.
California. California LID Portal. California Stormwater Quality Association.
New England. University of New Hampshire Stormwater Center – NEMO. Case studies.
Massachusetts. Boston Metropolitan Area Planning Council. LID Toolkit. Case studies, fact sheets, explanation of techniques, regulations and codes.
North Carolina. NC State University. Stormwater and LID publications.
Great Lakes. Lake Superior Streams. Site Design Toolkit. Site evaluation, policy, LID methods, case studies.
Handbooks, Manuals & Guides
Massachusetts. Massachusetts Bay Estuary Association. Greenscapes Guide.
New Jersey. New Jersey Department of Environmental Protection. Stormwater Best Management Practices.
Washington. Puget Sound Partnership. Technical Guidance Manual for Puget Sound.
California. San Diego County Department of Planning and Land Use. LID Handbook.
California. City of Salinas Development Standards Plan Low Impact Development Designs and Practices for Urban Storm Drainage Management.
Oregon. Portland Bureau of Environmental Services. Stormwater Solutions Handbook.
Great Lakes. Center for Neighborhood Technology. Water: From Trouble to Treasure. Pocket Guide to ‘Green' Solutions. Residential LID methods.
Hawaii. Coastal Zone Management. A Practictioner's Guide to Low Impact Development.
Maryland. Prince Georges County Department of Environmental Resources. Low Impact Development: An Integrated Designs Approach.
US Department of Housing and Urban Development. The Practice of Low Impact Development.
US EPA. Case Studies Analyzing the Economic Benefits of Low Impact Development and Green Infrastructure (PDF, 2 MB). A technical report to help utilities, state, other municipal agencies, and other stormwater professionals understand the potential benefits of low impact development and green infrastructure programs. The report highlights 13 case studies of selected public entities throughout the United States that have conducted economic evaluations of these programs.
Oregon. Oregon Sea Grant Extension. Soakage Trenches fact sheet.
Oregon. Oregon Sea Grant Extension. Stormwater Planters fact sheet.
USEPA. Office of Wastewater Management. Bioretention.
Low Impact Development Center. Low Impact Development (LID) Urban Design Tools Website. Tree box filters.
University of Maryland. Bioretention and Stormwater Research. Rain gardens.
Vegetative Strips, Buffers & Swales
Great Lakes. Lake Superior Streams. Site Design Toolkit. Grassy swales.
Virginia. Virginia Department of Conservation and Recreation Grassed Swale.
Oregon. Oregon Sea Grant Extension. Vegetated Filter Strips fact sheet.
Oregon. Oregon Sea Grant Extension. Swales fact sheet.
New Jersey. Native Plant Society of New Jersey. Rain garden manual and case studies.
New Jersey. Ocean County Soil Conservation District. Rain garden fact sheets, brochures and manuals. Low maintenance landscaping manual.
North Carolina. NC Cooperative Extension. Rain garden installation and maintenance.
Virginia Department of Forestry. Rain Gardens.
California. Surfrider Foundation. Ocean Friendly Gardens.
Maryland. Surfrider Foundation Ocean City Chapter. Aloha Garden. Wetland planting and maintenance for shore stabilization.
Washington. Surfrider Foundation Northwest Straights Chapter. Native Garden Project. Improve water quality, support ecosystem health, and scenic beauty.
Hawaii. Surfrider Foundation Maui Chapter. Native Plantings. Trap sediment in stormwater runoff, shoreline stabilization, ecosystem health & beauty.
Oregon. American Society of Landscape Architects. Mount Tabor Middle School Rain Garden. Art, education, and ecological function.
Oregon. Oregon Sea Grant. The Oregon Rain Garden Guide.
Oregon. Oregon Sea Grant Extension. Rain Gardens fact sheet.
Georgia. Clean Water Atlanta. Rain gardens for home landscapes.
Florida. City of Tallahassee. Rain gardens and rain barrels.
Michigan. Rain Gardens of West Michigan.
Texas. Austin City Connections. Rainwater Harvesting. Rain barrels.
Delaware. Broadkill Tributary Action Team. Rain barrels.
Center for Watershed Protection. How to install a rain barrel .
Green Roofs and Green Infrastructure
Oregon. Oregon Sea Grant Extension. Green Roofs fact sheet.
Oregon. Oregon Sea Grant Extension. Stormwater Planters fact sheet.
Washington D.C. American Society of Landscape Architects. Green roofs.
USEPA. Green roofs.
USEPA. Managing Wet Weather with Green Infrastructure.
California. Sea Grant. Porous Pavement.
California. Grass Parking.
Oregon. Oregon Sea Grant Extension. Porous Pavement fact sheet.
USDA. Natural Resources Conservation Service. Pervious Pavement.
Alternative Driveway & Parking Area Design
California. Sea Grant.
California. UC Cooperative Extension. Water Wise demonstration project, typical residence, retrofitted residence & LID designed residence.
Center for Watershed Protection. Manual 3. Urban Stormwater Retrofit Practices. Site evaluation and types of retrofits for residential sites, commercial sites, parking areas.
Saving and Amending Topsoil
California. Sea Grant. Saving & Amending Topsoil.
Low Impact Development Center. Soil amendments.
Fact Sheets & Educational/Outreach materials
California. Sea Grant. Green Building Info Sheets. Residential LID methods,bio swales, alternative driveway design, porous pavement, natural landscaping, saving and amending topsoil, tree cover.
Michigan. Landscaping for water quality: the LID approach. Michigan State University Extension.
Washington. Puget Sound Action Team. Low Impact Development Manual.
USDA Natural Resources Conservation District. Fact sheets, brochures, video, photo gallery, rain gardens, pervious pavement, soil amendments, bio swales, native plants.
USEPA. Green Infrastructure. Grassy swales, green roofs, porous pavement, rain gardens, bioretention, vegetated filter strips, rain barrels, cisterns, downspout disconnection, green parking, open space design.
Low Impact Development Center. Builder's guide to LID.
Local Ordinances & Regulations
Washington. Puget Sound Action Team. LID Regulatory Assistance Report.
California. Central Coast Regional Water Quality Control Board. LID requirements for new construction and redevelopment projects.
California. City of Los Angeles Stormwater LID Ordinance.
Rhode Island. Urban Coastal Greenways Policy. Metro Bay Special Area Management Plan. RI Coastal Resources Management Council. Vegetative cover and LID requirements.
Portland, Oregon. Green Street Program.
American Rivers. Local Water Policy Innovation. A Roadmap for Community Based Stormwater Solutions.
Center for Watershed Protection. Better Site Design: A Handbook for Changing Development Rules in Your Community. Model Ordinances.
California. State Water Resources Control Board. A Review of Low Impact Development Policies: Removing institutional barriers to adoption.
U.S. Navy. LID policy.
LID Regional Examples & Case Studies
USEPA. Case Studies Analyzing the Economic Benefits of Low Impact Development and Green Infrastructure (PDF, 2 MB). A technical report to help utilities, state, other municipal agencies, and other stormwater professionals understand the potential benefits of low impact development and green infrastructure programs. The report highlights 13 case studies of selected public entities throughout the United States that have conducted economic evaluations of these programs.
USEPA. Reducing Stormwater Costs through Low Impact Development (LID) Strategies and Practices. Cost and benefits evaluation. Case studies.
USEPA. Florida Aquarium case study.
District of Columbia. Center for Neighborhood Technology. Anacostia River & Washington Navy Yard stormwater retrofits.
NRDC. From Rooftops to Rivers. Stormwater control case studies.
- Chicago, Illinois
- Milwaukee, Wisconsin
- Pittsburgh, Pennsylvania
- Portland, Oregon
- Rouge River Watershed, Michigan
- Seattle, Washington
- Toronto, Ontario, Canada
- Vancouver, B.C., Canada
- Washington, D.C.
Massachusetts. Office of Energy and Environmental Affairs. Smart Growth/Smart Energy Toolkit. LID Case Studies.
Oregon. Portland Bureau of Environmental Services. Case studies.
Washington. Seattle Public Utilities.
California. Ventura River Ecosystem.
Milwaukee. Bradford Beach.
Illinois. Chicago's Green Alleys Handbook.
Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET). Tools for Clean Water and Healthy Coasts.
Bioretention cells. Product. Stormwater filter in urban and parking areas.
In the News
STORMWATER. Journal for Surface Water Quality Professionals.