structure. Following the three-part wetland delineation procedure adopted by federal agencies for defining wetlands in the CWA Section 404 program, wetland structure can be understood as some combination of hydrology, soil, and vegetation (NRC 1995). When planning a compensatory mitigation project, a wetland 's structure and location in the watershed are chosen to secure particular wetland functions. The plan might be based on a functional assessment that relates a wetland's structure and location to its function; alternatively, a compensatory mitigation project plan might seek to secure a particular type of wetland.

A compensatory mitigation site is initiated to satisfy a legal requirement of a permit program. A mitigation requirement is a condition of a permit that makes the permit recipient responsible for undertaking and executing a compensatory mitigation site or for paying a third party to take on that responsibility. As a legal matter, the mitigation requirement should establish a measurable outcome, called a performance standard, of a mitigation project. Performance standards can be measures of wetland structure or type or a functional assessment score. It may take several years before some measures of functional performance can be achieved at a mitigation project. However, mitigation agreements may avoid performance measures and instead require that, as a measurable outcome, the mitigation project be developed and implemented according to an approved plan. This can be referred to as a project design standard. Legal compliance with the compensatory mitigation requirement can vary from simply constructing a project according to some approved design (design standard) and/or to being tied to some measure of functional outcome (performance standard).

Wetlands occur in watersheds, which are defined in the glossary of this report as “land area that drains into a stream, river, or other body of water. ” However, a watershed is not area specific, because it can range from a small area near a creek to the entire Mississippi River basin. When positions or management of wetlands within watersheds are discussed, the larger scale is indicated. Discussion of planning for wetland mitigation within watersheds indicates a scale on the order of an ecoregion. The terms landscape and watershed are often used interchangeably.

It follows that there are distinct stages in any compensatory mitigation project; each stage requires an action to be taken that will increase the probability that the compensatory mitigation project will attain its intended results. First, there must be a concept and a general watershed location for the compensatory project. Second, that concept must be translated into a set of site design plans that are expected to secure the target functions over time. Third, the site would be acquired and construction (or other modifications to it) would be undertaken in accord with the design. Inspection of the site would be made to establish whether the

The National Academies of Sciences, Engineering, and Medicine
500 Fifth St. N.W. | Washington, D.C. 20001

Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement