In 1991, the Corps of Engineers expanded the Wetlands Research Program at the Environmental Laboratory, Vicksburg, MS, now a part of the U.S. Army Engineer Research and Development Center, and its efforts to develop a wetland assessment technique that could meet the unique requirements of the Corps regulatory mission. The Hydrogeomorphic (HGM) Approach to Assessing Wetland Functions is the product of that effort. Although initially developed for Corps of Engineer regulatory needs, the HGM Approach can be applied to a wide variety of other uses that require examination of potential impacts on wetlands. It can be used to assess the effectiveness of mitigation plans to compare conditions before and after project implementation, and to project the future with and without a project.
The basic concepts of the HGM Approach were published in 1995 (Smith et al. 1995). A national guidebook was also prepared (Brinson et al. 1995) for riverine wetlands to serve as a template for developing region-specific guidebooks that could then be used to conduct wetland assessments. An approach to classification for grouping wetlands into similar classes was also developed (Brinson 1993) to facilitate wetland assessments. On 24 August 1993 the White House Office on Environmental Policy released the Clinton Administrationís comprehensive package of improvements to the Federal wetlands program. It stated that "The agencies will expedite development of a new approach for wetland functional assessment known as the Hydrogeomorphic Classification System (HGM). It also stated that Executive Order 11990 would be revised ... to direct the Federal agencies to take a watershed/ecosystem approach to wetlands protection and restoration."
In response to the White House Office on Environmental Policy document, several Federal agencies that work closely with regulating, managing, or impacting wetlands formed a National Interagency Implementation Team. The Team consists of representatives from the Corps of Engineers including the Environmental Laboratory, the U.S Environmental Protection Agency, the U.S. Department of Agriculture Natural Resources Conservation Service, the U.S. Fish and Wildlife Service, the Federal Highway Administration, and the National Oceanic and Atmospheric Administration National Marine Fisheries Service. This Team developed a National Action Plan that provides a strategy the Corps and other Federal agencies will follow to implement the HGM Approach. The Plan identifies the role each of the agencies will perform, provides guidance for quality control for regional guidebook development, training and outreach, and publication sequence; and assigns the Environmental Laboratory as the Technical Support Center for development of the HGM Approach. There has been a growing awareness of wetland functions and the values to society by the scientific and public communities, leading to several legislative mandates to examine projects that may have negative impacts on wetlands and the necessity to develop techniques that can be used to assess wetland ecosystems. The HGM Approach is a consequence of this evolutionary process and thinking. The concepts and principles of HGM have been expanded to include streams and other aquatic ecosystems.