A More Natural Approach
Low impact development finds a place in local government stormwater ordinances
- By Jon E. Kallen
- Apr 01, 2005
Low Impact Development (LID) is an environmentally sustainable approach to stormwater management that offers an attractive alternative to conventional management techniques. Local and state planners and government officials are becoming more receptive to incorporating LID approaches into stormwater, zoning, and site development ordinances. In 2003, two Virginia jurisdictions in the Chesapeake Bay watershed incorporated LID approaches into their local zoning ordinances, signaling a new trend in overall stormwater management.
LID is an approach that attempts to achieve stormwater control through the development and effective implementation of a hydrologically functional landscape that mimics natural systems. LID specifically aims to preserve open space and minimize land disturbance while protecting natural systems and processes. LID techniques attempt to incorporate natural elements into site design and manage stormwater at its source with the ultimate goal of preserving pre-development hydrology and water quality.
Conventional Stormwater Management
LID as a stormwater management approach differs in key respects from conventional stormwater management. The ultimate objective of conventional stormwater management is to concentrate, collect, and convey stormwater runoff for treatment. The old paradigm was to achieve good drainage by removing undesirable stormwater runoff from a site as quickly as possible. In order to achieve this primary objective, every feature of a conventionally developed stormwater system is designed to convey runoff to a centrally located management device. Roadways, roofs, gutters, downspouts, curbs, pipes, drainage swales, and site grading are all designed for rapid disposal of the runoff. These efficient drainage systems have resulted in an increase in runoff volumes, flows, and frequency of discharges, all to the detriment of natural systems.
This conventional stormwater management approach requires development of infrastructure that includes drainage piping, culverts, curbing, gutters, as well as stormwater outlets and management ponds. This infrastructure requires extensive site clearing and development with the associated capital outlays. Additionally, this established stormwater conveyance infrastructure requires long-term inspection and maintenance. These inspection and maintenance costs are often a financial burden on property owners, developers, and local governments.
LID Design and Implementation Strategies
LID as a stormwater management tool revolves around several interrelated design and implementation strategies that are integral to the entire process. All of these strategies are discussed in detail in a manual produced by the Prince Georges County, Maryland, Department of Environmental Resources entitled, Low Impact Development Design Strategies -- An Integrated Design Approach. First and foremost, LID attempts to reduce the overall "footprint" of a developed site. For a new development, this strategy would involve attempts to reduce the extent of site clearing and grading in order to minimize hydrologic impacts. LID attempts to minimize imperviousness by reducing both the total area of paved surfaces and the compaction of highly permeable soils. Efforts also are made to minimize changes to existing site topography and drainage. The goal is to reduce runoff while encouraging infiltration, runoff storage, and evapotranspiration. Related to the reduction in the overall footprint of a site, LID also attempts to minimize directly connected impervious areas. Techniques for accomplishing this include disconnecting roof drains and directing stormwater flows into natural, vegetated buffer areas. These vegetated areas are better able than paved, impervious areas to filter and drain stormwater, reducing the overall sheet flow.
LID strategies also seek to increase drainage flow paths in order to increase the time of concentration (Tc) of stormwater. Time of concentration is defined as the time it takes for surface runoff to travel from the farthest point of the watershed to the stormwater outlet. Factors affecting Tc include travel distance, overall flow path, slope of the ground surface, surface roughness, and slope of the stormwater channel. Tc can be increased by designing and implementing overall site conveyance systems that lengthen and flatten site and slopes, increase and lengthen flow paths, and increase surface roughness through increased vegetation. All of these techniques serve at least to restore Tc to predevelopment levels. Finally, integrated management practices (IMPs) should be a key component of any LID design and implementation. IMPs are used to convey runoff through the site while providing unlimited opportunities for infiltration and treatment of runoff. Some common IMPs include filter strips, vegetated swales, permeable pavements with underdrains, and bioretention ponds or cells.
Integrating LID into site design and overall stormwater management will benefit the natural environment and overall regional water quality while resulting in cost savings. LID saves money because it requires less land clearing and grading and does not require extensive site stormwater infrastructure and utility development such as conveyance piping, drains, inlets, and curbs. Less stormwater infrastructure will result in long-term savings on routine maintenance and upkeep of these systems. In addition to these site development savings, LID will result in more livable communities by maintaining and protecting local flora and fauna. The natural filtering qualities associated with LID design strategies will also protect and enhance water quality by reducing sediment, nutrient, and heavy metal loads.
Adopting LID: A Tale of Two Cities
LID is a promising site development and stormwater management approach. However, it runs counter to traditional zoning regulations, which often have stringent requirements for impervious pavements and conventional stormwater conveyance infrastructure, including drains, curbs and piping. Therefore, implementing LID may require modification of existing local ordinances. Successful efforts have been undertaken in two areas of Virginia to incorporate LID techniques into stormwater management and local zoning applications. These two cases provide useful guidance on how to successfully incorporate LID into local ordinances.
Town of Warsaw, Va.
The Town of Warsaw is a rural locality located in Richmond County on the Northern Neck of Virginia. The Northern Neck is a peninsula flanked by the Potomac River on the north and the Rappahannock River to the south. Both rivers are key tributaries of the Chesapeake Bay.
The town was a municipal partner in a grant awarded by the U.S. Environmental Protection Agency (EPA) Chesapeake Bay Programn to two non-profit organizations, the Friends of the Rappahannock (FOR) and the Low Impact Development Center. The purpose of the grant was to develop guidance and strategies for rural communities in Virginia to incorporate LID into their local regulatory programs. According to John Tippett, executive director of FOR, town officials had expressed an interest in LID primarily because they were concerned about the costs of stormwater infrastructure associated with future development. The Warsaw town manager, John Slusser, was interested in incorporating LID into the undeveloped land that the town had recently annexed from the county for the development of an industrial park. According to Tippett, Slusser was concerned about the costs associated with the development of stormwater infrastructure for this parcel of land and saw LID as a way to reduce costs, increase environmental protection, and enhance the land's aesthetic appeal.
FOR's Tippett stated that this entire process was designed around the development of a plan to institute LID as the "standard development approach town-wide." The first issue related to LID program design and implementation to emerge was the absence of criteria for local government plan reviewers to apply in assessing LID design. There was also concern that the development community was unaware of the LID approach to site design and stormwater management, and would find it difficult to submit quality LID plans. Based on this evaluation, it was determined that a stormwater management policy for instituting LID as the standard practice for project site design and stormwater management needed to be developed. LID review guidelines for local planning staff and a reference document for developers to use in designing LID plans were also needed.
The actual policy language developed for the town establishes LID as the standard approach for stormwater management. Specifically, this policy document references the LID national manual (see Low Impact Development National Hydrology Manual, EPA 841-B-00-002). for design guidelines, allows for devices including bioretention, infiltration trenches, soil amendments, and increased vegetation to increase infiltration, and states that post-development Tc will be no less than pre-development Tc.
The town adopted this specific LID policy document language as an ordinance in August 2003. The policy language was incorporated into sections 4-6-1 and 4-6-2 of the Town of Warsaw's Development Management Ordinance. This ordinance firmly states that the Town of Warsaw endorses LID and that all drainage plans are required to implement LID unless they can demonstrate that it is impractical. FOR's Tippett states that "all future development in the town needs to use LID but if developers cannot make it work successfully they can attempt to receive a waiver."
Stafford County, Va.
Stafford County, Va, is located midway between the metropolitan areas of Washington, D.C., and Richmond, Va.. The county encompasses 277 square miles and has a population of approximately 92,000. The county is experiencing rapid residential and commercial growth resulting from its prominent location near Washington along the Interstate 95 freeway. The Rappahannock River, a major tributary of the Chesapeake Bay, flows along the southern boundary of the county.
The Friends of the Rappahannock was once again instrumental in leading the efforts to develop and integrate LID into the county's ordinances. Tippett stated that FOR and the county saw LID as an effective approach to improving stormwater management at the county's many newly constructed developments, which in turn would help the county meet the stringent nutrient and sediment load reductions stipulated in the Virginia Tributary Strategy, part of the Chesapeake Bay 2000 Agreement. Beginning in 1999 and continuing up to implementation in 2003, FOR coordinated educational projects to prepare county staff and elected supervisors for the task of revising the county code. According to Tippett, the county has a regular process for reviewing and updating its codes including stormwater provisions. Working with the county's Code Administration Department, FOR and other community stakeholders created a LID committee that proposed specific regulatory changes to the county code. In March 2003, the county board of supervisors passed two ordinances. One adopted in its entirety a new stormwater management ordinance (Ordinance 003-12); the other amended the subdivision and zoning ordinance (Ordinance 003-26) to provide the mechanisms and incentives for developers to implement LID stormwater management design plans.
The revised and updated stormwater management ordinance adopted the LID approach, specifically allowing developers and site planners to choose either LID or conventional stormwater management at the beginning of the site development process. This updated ordinance also provides for the adoption by reference of the national LID hydrology reference manual, provides specific guidelines for implementing LID, and removes actual LID prohibitions previously contained in the code. According to Tippett, "the previous prohibition against on-lot stormwater management was removed, opening the door for LID approaches."
With the changes to the subdivision and zoning ordinance, there are now specific incentives for developers to choose LID for sites. According to Tippett, one incentive allows developers who incorporate LID into site development to construct vegetated swales instead of curbs and gutters for stormwater management. Another incentive allows developers to construct trails instead of sidewalks through common green space. The successful adoption of LID in both Stafford County and the Town of Warsaw, Va., appears to be a win-win strategy for developers, planners, and environmentalists.
Prince Georges County, Md., Department of Environmental Resources, Programs and Planning Division, Low-Impact Development Design Strategies -- An Integrated Design Approach, June 1999.
Stafford County, Va., Stormwater Management Design Manual, March 2003.
Town of Warsaw, Va., Low Impact Development Stormwater Management Policy.
Low Impact Development National Hydrology Manual, EPA 841-B-00-002.
Friends of the Rappahannock, 2002 Annual Report.
Friends of the Rappahannock Web Site, www.riverfriends.org.
Low Impact Development Web Site, www.lowimpactdevelopment.org.
Stafford County, Va. Stormwater Management Ordinance (Ordinance 003-12).
Stafford County, Va. Subdivision and Zoning Ordinance (Ordinance 003-26).
Town of Warsaw, Va. Development Management Ordinance, Sections 4-6-1 and 4-6-2.
This article originally appeared in the 04/01/2005 issue of Environmental Protection.