Low Impact Development: Moving towards economically sound environmental asset management
Neil Weinstein, P.E., R.L.A., AICP
The Low Impact Development (LID) Center, Inc.
Interest shown by local government in the Low Impact Development (LID) approach to stormwater management has grown exponentially over the last several years. This new approach has gained wide acceptance by regulators, municipal stormwater managers, engineers, watershed planners, citizens groups, and environmental organizations. Not only are there environmental benefits but also economic and community development potential.
LID is a decentralized stormwater management strategy that uses natural processes, such as the interception and uptake of stormwater by plants, infiltration devices, and detention to mimic the watershed's pre-development water balance and hydrology. LID uses a combination of pollution prevention, conservation and site design techniques to minimize impacts. Small-scale Best Management Practices (BMPs) help to control the volume, frequency, duration, and peak rates of stormwater runoff. These practices also filter and treat pollutants by biological, chemical, and physical processes. These processes reduce the volume of pollutants by infiltration, conservation, or uptake by plants. These water-handling BMPs can be designed into almost every aspect of the urban landscape. There is an endless and diverse combination of practices that may include: landscaping treatments, tree wells, bioretention areas, vegetated roofs, permeable pavements, and cisterns.
LID was pioneered by the Prince George's County (MD) Department of Environmental Resources in the mid-1990s under the leadership of Larry Coffman, who championed bioretention, one of the foundations of LID. Bioretention, or rain gardens, are small landscaped areas that contain an engineered soil mixture and specialized plants that treat stormwater. Prince George's County has one of the best-funded and well-respected stormwater programs in the country. Coffman recognized that the stormwater infrastructure being maintained by the County was growing and aging. He also recognized that many of the conventional stormwater management strategies, practices, and permit requirements, although easy to administer, were not meeting resource protection goals. Once installed, these facilities were also impossible to maintain, not attractive and not being accepted by the communities. As such, the facilities were becoming health and economic burdens to the communities.
LID offered the opportunity to customize the performance of BMPs so that they could address targeted issues, such as Total Maximum Daily Loads (TMDL) or Municipal Separate Storm Sewer System (MS4) Permit requirements. The ability to design stormwater functions into the landscape also created an opportunity to leverage funding for facilities and provide opportunities for public and private partnerships or funding options. The ability to construct facilities on private properties is especially important in urban areas where stormwater utilities are being considered, since this practice can be used to reduce the public construction and maintenance burden.
In 1998, when the LID Center, a nonprofit 501(c)(3) water resources research organization, began, LID was only being discussed as a long-term option. The initial studies by the LID Center that were funded through grants from the USEPA Office of Water, USEPA Region 3, and the Chesapeake Bay Program on the use of LID for urban area retrofits to alleviate Combined Sewer Overflows (CSOs) helped spur a national movement for the use of LID and for LID research. The tremendous cost of using centralized tunnels to detain runoff, mitigate CSOs, and meet MS4 requirements was a problem faced by over 1,000 communities in the U.S. Many developed communities also lacked the open area to install traditional stormwater control facilities. These factors and an ever-increasing competition for funding with other programs, such as education and public safety, have lead to the wide-scale acceptance of the LID approach.
LID technology is being used by the Department of Defense (DoD) for compliance and natural resource management. The LID Center recently completed a design manual for the U.S. Navy for use by all DoD organizations. As bases experience infill homeland security development and Base Realignment and Closure (BRAC) activities, the need to preserve infrastructure capacity requires the retrofitting of areas with minimal disruption to activities.
This technology is also being used by state highway departments, including Washington State, Washington, D.C., Maryland, and North Carolina. This is because LID allows efficiency, the ability to customize practices, small facilities footprints, and generally low maintenance requirements. The flexibility to design practices to address targeted pollutants and the small footprint that conserves right-of-way acquisition costs are critical benefits of this approach.
The Water Environment Research Foundation (WERF) and the National Cooperative Highway Research Program (NCHRP) are currently sponsoring large-scale research efforts in conjunction with the Center. The research is to help communities and transportation organizations develop strategies to integrate LID into their compliance and resource protection programs.
One of the great opportunities for LID is its use as an economic and community development tool. LID is being integrated into the Leadership in Energy and Environmental Design (LEED) program as part of its overall water and energy conservation programs. Stormwater is typically managed as a program or requirement separate from other infrastructure programs. This separation results in a lack of economical integration with building or site programming components. Because LID can be integrated into buildings or landscapes, it can now be an economic asset as well as a compliance tool. Many cities are requiring LEED ratings for their municipal buildings. LID techniques such as vegetated roofs, low water use irrigation systems, bioretention planters and tree box filters are being used to meet these requirements and to reduce stormwater permit and utility fees. A side benefit of LID is the potential for the improved appearance of an urban streetscape in a highly environmentally efficient and cost-effective manner.
The future and potential for LID are extremely bright. But questions still remain about the long-term effectiveness and continuity of this approach. Decentralized controls have been used extensively in Europe and Asia for many generations; however, experience with LID in this country is limited. Studies of communities such as Village Homes in Davis, California have shown that homeowners have embraced and enhanced this concept over long periods of time and on properties with many different owners and residents. Universities and institutions are studying the long-term effectiveness and maintenance requirements. Still, many of the long-term management costs and considerations are still not fully known for many communities.
One of the easiest and most successful ways for communities to evaluate LID is to construct pilot projects that involve the stakeholders (designers, municipal managers, developers, and public works enforcement and maintenance personnel). These projects can be constructed through grants or special programs that reduce the perceived "risks" and apprehension associated with new techniques. Once all the construction and management issues are explored and addressed, communities can develop and integrate LID into development and regulatory programs that are best suited for their long-term compliance and resource protection efforts.
Neil Weinstein can be reached at (301) 982-5559 or at email@example.com. For more information on the Low Impact Development (LID) Center, Inc., a nonprofit 501(c)(3) water resources research organization dedicated to the advancement of Low Impact Development technology, go to www.lowimpactdevelopment.org.