March 2009, Vol. 21, No.3

Research Notes

Decentralized Stormwater Controls for Urban Retrofit and CSO Management

The second phase of a recently completed two-part study funded by the Water Environment Research Foundation (WERF; Alexandria, Va.) assesses the use of decentralized stormwater controls for urban retrofit and combined-sewer overflow management.

According to the final report, understanding how best to use decentralized controls involves considering the role that they will play in the urban environment. Compared to conventional “gray” infrastructure, decentralized controls provide a “greener,” more sustainable urban design. Because decentralized controls rely heavily on vegetation or practices that simulate elements of the natural hydrologic cycle, the environmental benefits gained extend beyond stormwater and water quality.

There is a growing “green city” movement as municipalities recognize and seek to capitalize on the many benefits of incorporating green space and green design into the urban environment, the report notes. According to the report, decentralized storm-water controls can play a productive role in this movement and in addressing various environmental issues confronting urban areas, including


  • the urban heat–island effect,
  • air quality,
  • energy,
  • climate, and 
  • aesthetic and community benefits.

The report indicates that decentralized controls offer an integrated approach to comprehensive environmental management. Their unique qualities alter the traditional approach to pollution abatement and present a multimedia, multibenefit solution. But this new strategy also presents challenging institutional barriers. The report provides illustrative examples of typical decentralized controls applied in various scenarios, including dense urban areas, transportation corridors, parks, and suburban residential areas.

Several planning and implementation scenarios likely to provide opportunities to encourage the use of decentralized controls include

  • pilot installations by an agency or organization at any level;
  • watershed-based approaches, which typically will be overseen by a regional or higher-level authority;
  • building and site redevelopment projects, which work to implement distributed controls as part of their building process; and
  • large-scale urban revitalization projects, which often will be a collaborative process among several agencies at a variety of levels, including private developers.

The report provides detailed information and examples for each of these implementation scenarios. In all cases, the coordinated effort of technical and planning staffs and elected officials is critical to the success of a distributed, yet integrated system, the report says.

The report also presents methods for evaluating economic considerations when implementing decentralized controls. The multiple benefits provided by decentralized controls necessitate more comprehensive methods of economic valuation than those traditionally used to assess stormwater and combined-sewer overflow programs, the report states.

For more information on the report (Project No. 03-SW-3a) and related research, see, or contact Jeff Moeller at

©2009 Water Environment Federation. All rights reserved.