Upper Yellowstone River Hydrogeomorphic Functional Assessment for Temporal and Synoptic Cumulative Impact Analyses

Abstract : Until recently, methods of evaluating wetland loss or degradation were either so generalized that detection of change was not quantifiable or required exhaustive research beyond the human or financial resource scope of a regulatory program. The hydrogeomorphic (HGM) approach to the functional assessment of wetlands was specifically developed, principally by the U.S. Army Corps of Engineers and other Federal and state agencies throughout the United States, as a comprehensive framework for rapid evaluation of wetland ecosystem function (Smith et al. 1995). The HGM approach is implemented at the local or regional level through the identification of a series of functions performed by the wetland subclass, followed by development of regional guidebooks containing logic models that represent the functions. The logic models are composed of variables that degrade correlatively with level of human impact and play a vital role in the function described by the model. The output of each model is an index scaled from 0 to 1.0, where 0 represents a completely altered condition such that the function no longer occurs and 1.0 represents the unaltered, naturally occurring level of function. Thus, the functional capacity index (FCI) scores of subject wetlands are based on a reference data set that captures the range of variation of impact for the regional subclass.