WETLANDS, Vol. 18, No. 3, September 1998, pp. 379-392 © 1998, The Society of Wetland Scientists A RAPID IMPACT ASSESSMENT METHOD FOR USE IN A REGULATORY CONTEXT Eric D. Stein U.S. Army Corps of Engineers Los Angeles District, Regulatory Branch P. 0. Box 532 711 Los Angeles, California, USA 90053-2325 Richard E Ambrose Environmental Science and Engineering Program University of California, School of Public Health 10833 LeConte Avenue Los Angeles, California, USA 90095-1772 Abstract: Assessing the impacts of projects that affect aquatic resources is an integral part of regulatory programs. The time, resource, and technical requirements of existing assessment methods often prohibit their routine use by regulatory staff. Consequently, many evaluations are based on area affected and best profes- sional judgment. In this paper, we present a Rapid Impact Assessment Method (RIAM) that can be used to assess impacts to aquatic resources in a manner that is scientifically defensible, yet easy to implement by regulators, planners, and resource managers. The RIAM provides a framework for assessing impacts while allowing for specialization of evaluation criteria based on the habitat type, region of interest, and specific regulatory, planning, or management goal. Site-specific impacts are assessed by comparing the conditions present at each site prior to project implementation to conditions present after implementation of the project. A set of evaluation criteria is defined to reflect the important ecological characteristics to be evaluated. Each project site is given a pre- and post-project rating for each evaluation criterion, ranging from A for site conditions similar to those present at reference sites to E for the most degraded condition. Impact scores for each criterion, ranging from -4 to +4, are based on the difference between the pre- and post-project rating levels at each site. We demonstrate the application of the R/AM by using it to assess the impacts of projects permitted under Section 404 of the Clean Water Act on the following six evaluation criteria: endangered species habitat, structural diversity of habitat, spatial diversity of habitat, open space habitat, linear contiguity of habitat, and adjacent habitats. In the future, the method developed in this study can be used as a predictive tool to help monitor impacts on an ongoing basis. Key Words: habitat assessment, impact assessment, habitat functions, semantic categorization, Section 404, riparian habitat, Southern California INTRODUCTION Environmental regulations and general concern over the effect of human actions on natural systems have led to the development of many techniques to assess ecological functions and the impacts of human activity (Margules and Usher 1981, Adamus 1983, Lonard and Clairain 1985, Preston and Bedford 1988, USACOE 1988, PERL 1990, Croonquist and Brooks 1991, USE- PA 1992, Bartoldus et al. 1994, Brinson et al. 1994). The underlying goal of ecological functional assess- ment techniques is to evaluate the capacity of a habitat to perform a particular ecological function, such as provision of foraging or breeding habitat for birds or retention of suspended particulate matter. The goal of impact assessment is to evaluate how a given activity has altered an ecosystem's capability to perform those functions. Impact assessment is integral to the U.S. Army Corps of Engineers (Corps) regulatory program under Section 404 of the Clean Water Act (CWA) of the United States. Section 404 of the CWA regulates the discharge of dredged material and placement of fill material within waters of the United States, such as lakes, streams, estuaries, and wetlands. Clean Water Act regulations at 40 CFR Part 230 require the Corps to collect information regarding impacts and use this information as the basis for permit decisions, mini- mization recommendations, and mitigation require- 379