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3.1C – Planning and Design – Impervious Surfaces

Management Measure

Limit or reduce the amount of impervious areas

In most cases, when impervious cover (IC) is less than 10 percent of a watershed, streams remain healthy. Above 10 percent impervious cover, common signs of stream degradation are evident. They include (Center for Watershed Protection 2003, Booth 1991).

  • Excessive stream channel erosion (bed and bank)
  • Reduced groundwater recharge
  • Increased size and frequency of 1-2 year floods
  • Decreased movement of groundwater to surface water
  • Loss of streambank tree cover
  • Increased contaminants in water
  • Increased fine sediment in stream bed
  • Overall degradation of the aquatic habitat

Management Practices

Limit increases of impervious surfaces

Developers can use innovative site and structure designs that reduce building footprints, decrease the amount of paved infrastructure, and provide for dispersed drainage and infiltration of runoff from impervious surfaces to reduce "effective impervious surface," which can be defined as impervious surface that is connected to the storm water drainage system. The concept of effective impervious surface is important, because when runoff from these surfaces is directed to pervious areas rather to an impervious drainage system (i.e., curbs, gutters, street surfaces, storm drain pipes), it can infiltrate, evaporate, or be taken up by vegetation, thereby reducing the total volume of runoff leaving a site.

The following techniques, among others, can be used as appropriate to reduce the impact of an individual development site to receiving waters. Municipalities can require that these types of practices be implemented through an ordinance that provides modified, environmentally friendly standards for infrastructure dimensions and layouts. In addition, these practices can be encouraged through storm water credits or density credits provided as incentives to developers. Some of the techniques include:

  • Designing streets to be narrower
  • Placing sidewalks on only one side of the street
  • Providing pervious areas (via porous pavement) for on-street parking, parking lots, alley-ways, and drive ways – avoid using near toxic hot spots or 100 feet from drinking water wells
  • Redesigning the layout of buildings to reduce street length and preserve open space
  • Increasing density for residential housing
  • Reducing parking lot sizes and parking space sizes
  • Promoting shared parking among nearby businesses with different peak demands for parking (e.g., churches and retail businesses)
  • Disconnecting impervious surfaces through creative grading plans and distributed infiltration areas (see MM 3.1D, Landscaping)

Runoff treatment facilities can be located within existing right-of-ways, medians, or interchange loops, or on adjacent lands (e.g., golf courses and parks). Where no additional land is available, underground runoff storage and treatment (e.g., sand filters) can be used. Vegetative filter strips along roadsides and in medians can be effective at slowing runoff velocities and increasing storm water infiltration (see Wetlands MM 6C, Vegetated Treatment Systems).

Programs

  • Chicago, Green Alley Program is a new approach designed in reaction to constant flooding of alleyways not connected to the City’s combined sewer-stormwater system. This program utilizes permeable pavement and bifiltration basins.
  • Green Highways Partnership (GHP) is a voluntary, public/private initiative that is revolutionizing our nation's transportation infrastructure. Through concepts such as integrated planning, regulatory flexibility, and market-based rewards, GHP seeks to incorporate environmental streamlining and stewardship into all aspects of the highway lifecycle.
  • LID Center, Green Highways and Green Infrastructure Program, Green Infrastructure approach to infrastructure planning, design, and construction is a revolutionary approach to resource protection and environmental compliance. The approach is based on providing predictable pathways to streamline the delivery of transportation projects by the use of incentives and recognition for the use of innovate stormwater and environmental designs that are done in the context, or framework, of a watershed approach.
  • Portland Green Streets Program was approved a Green street resolution, report, and policy to promote and incorporate the use of green street facilities in public and private development. Portland has also adopted a progressive Division Green Street/Main Street Plan to create a pedestrian-friendly commercial district that reflects and reinforces community values, including a focus on sustainable and "green" development. Community interest in sustainable practices encompasses a broad spectrum of ideas and strategies, however, this project looked specifically at green infrastructure opportunities at a conceptual level within the public right-of-way. This was done through a transportation and land use planning process that included extensive community, business and interagency collaboration.

Information Resources

  • Low Impact Development Center contains technical references for implementing low impact development techniques and has case studies of sites where these practices have been successfully implemented.
  • Green Development Literature Search this document is a collection of examples, case studies, and issues related to urban development and the implementation of Green Development, prepared for USEPA’s Office of Wetlands, Oceans, and Watersheds. Information contained in this collection can be used to promote better approaches to development and management of development impacts through the use of alternative site planning, zoning, grading, natural resources protection, site layout, and storm water management options.
  • Congress for the New Urbanism, Reduced Width Street Standards Database contains jurisdictions across the country that have adopted reduced width street standards. The database also includes resources related to neighborhood design and transportation.
  • Dan Burden, Street Design Guidelines for Healthy Neighborhoods, this guidebook will help communities implement designs for streets that are safe, efficient and aesthetically pleasing for both people and cars. It features helpful guidelines that specify street widths and implementation strategies developed by a team of experts.
  • Delaware Department of Natural Resources and Environmental Control Green Technology: The Delaware Urban Runoff Management Approach is a technical manual that reviews impacts of urban runoff on stream ecosystems and riparian zones. The manual presents how green technology management practices can effectively address these impacts and how to properly design the most appropriate management practice. The document includes chapters on construction and testing specifications, design standards and specifications, landscaping standards and specifications, summaries of standards for management practices, and a set of typical details for each type of management practice.
  • LID, Urban Design Tools, Permeable Pavers: provides watershed managers with a new set of tools and techniques that can be used to meet regulatory and receiving water protection program goals for urban retrofits, re-development projects, and new development sites.
  • LID Center, Permeable Interlocking Concrete Pavement Specification.
  • Stormwater, March/April 2005, Advances in Porous Pavement.
  • ToolBase Services, permeable pavement. ToolBase is the housing industry's resource for technical information on building products, materials, new technologies, business management, and housing systems. This site provides some information on permeable pavement.
  • USEPA, Parking Spaces/Community Places: Finding the Balance through Smart Growth Solutions, this report presents options for managing parking using innovative alternatives involving reduction in oversupply of parking spaces, managing demand for parking, and developing pricing strategies. The report includes a discussion of the costs of parking and case studies from across the country.
  • USEPA, Porous Pavement BMP Factsheet.

References

Booth, Derek B. 1991. Urbanization and the Natural Drainage System-Impacts, Solutions, and Prognosis. The Northwest Environmental Journal 7.1: 93-118.

Center for Watershed Protection. 2003. Impacts of Impervious Cover on Aquatic Systems, Ellicott City, MD.

Maxted, J.R., and Scoggins, M. 2004: The ecological response of small streams to stormwater and stormwater controls in Austin, Texas USA. Prepared by the Watershed Management Institute for the United States Environmental Protection Agency, Office of Water, Office of Science and Technology, Washington DC; Cooperative Agreement 9701.

USEPA. 2005. National Management Measures to Control Nonpoint Source Pollution from Urban Areas. EPA 841-B-05-004. U.S. Environmental Protection Agency, Washington, DC. Downloaded from http://www.epa.gov/owow/nps/urbanmm on March 3, 2008.

 

(Updated 9/4/08)