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Publication Abstract

Land and Hydrologic Analysis for Stormwater Detention and Volume Control Trading Exchange in Cook County, Illinois Allan, Kingsley, Clayton Ballerine, Mary Pat McGuire, Sally McConkey,  Illinois State Water Survey, Champaign, IL,  ISWS CR 2017-04    Full Text Available

The Cook County Watershed Management Ordinance (WMO) allows detention trading as an option for providing off-site stormwater management for a given project as an alternative to on-site detention as part of an individual site development. Volume control (also referred to as retention) trading is proposed in the WMO Draft Amendment. As part of the effort to evaluate a potential stormwater detention and volume control trading exchange, the Illinois State Water Survey (ISWS) was contracted to assess potential opportunity areas for developing stormwater management facilities (detention and/or volume control) in suburban Cook County, excluding the City of Chicago. The ISWS land and hydrologic analyses compose one of three coordinated projects that explore the feasibility of stormwater trading in the study area. The ISWS was contracted by the Metropolitan Water Reclamation District of Greater Chicago, which led the land and hydrologic analyses team. A real estate demand analysis was performed by a team composed of Teska Associates, Inc.; Hey & Associates, Inc.; and Orion Planning and Design. The Nature Conservancy and the Metropolitan Planning Council led the policy analyses team. Studies and analyses were coordinated, and each team prepared a report. This report describes the analyses performed by the ISWS.

The primary objective of the land and hydrologic analysis component of the feasibility study is to identify and quantify opportunity areas with favorable characteristics for stormwater detention or volume control. The analyses were performed on a geospatial platform, building on Geographic Information System (GIS) tools. Opportunity areas could be used to provide trading credit when a development cannot meet the requirements on-site. The analyses used to identify opportunity areas are based on existing and available geospatial data that determined the precision of the results. Desirable characteristics differ for detention and volume control facilities; thus, two sets of data compilations were prepared, one showing opportunity areas for detention and one for volume control. This feasibility assessment study showed there are ample opportunity areas for trading. Supply of opportunity area is clearly not a limiting factor in a potential market. However, these areas have not been developed before and incentivizing creation of stormwater detention and/or volume control sites for trading will be important to avoid supply constraints. The GIS tools developed as part of this study will help to identify potential sites to assist with catalyzing this trading initiative.

Site development that uses off-site stormwater detention or volume control will meet the basic precepts of the WMO. Off-site storage upstream of the development site could reduce peak flows upstream, providing additional benefits to the area. Likewise, off-site volume control holds great promise in spurring the creation of the natural, multifunctional sites that enhance the study area and provide ecological and economic benefits.

Stormwater landscapes, sometimes called “landscape as infrastructure” become highly important public and environmental spaces in municipalities. Recent research has revealed that stormwater landscapes create multiple benefits to communities visually, educationally, socially, and environmentally. Therefore, the relative “value” of given sites and their characteristics may differ among different subwatersheds and communities depending on issues and priorities. The methodology for site selection can be adapted for use by watershed or community planners to locate sites with the greatest potential to serve their development priorities and achieve the desired ecosystem benefits.

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