A Brief Overview of FACWet
FACWet has its roots in Hydrogeomorphic (HGM) theory developed by Mark Brinson in the early 1990’s; however, it is important to note that FACWet uses a very different approach to wetland assessment than other HGM-based methods that are often synonymized with HGM theory and its wetland classification scheme.
FACWet applies the conceptual framework that wetland functioning and condition can be decomposed into a relatively small number of ecological forcing factors. FACWet considers three primary attributes of wetlands, and each attribute is described by ecological forcing factors, which are termed “state variables”:
· Buffer and Landscape Context;
· Habitat Conductivity
· Contributing Area;
· Hydrology; and
· Water Source;
· Water Distribution (within the wetland);
· Water Outflow;
· Abiotic and Biotic characteristics.
· Chemical Environment; and
· Vegetation Structure and Complexity.
Using a weight-of-evidence approach, the composite condition of these variables is used to describe the condition and functioning of the assessment wetland relative to its natural or “reference standard” condition. FACWet provides an information framework within which evidence of all qualities can be placed. In routine application, evidence is provided in the form of rapid assessment observations and best professional judgment. A FACWet evaluation can just as well be backed by detailed quantitative information.
Using scoring guidelines provided in the user guide and data sheets, evaluators rate the condition of variables on a scale from 1.0 (pristine/reference standard) to 0.0 (non-functioning). To maximize the intuitiveness of scoring, this rating scale parallels the academic grading scale, where 1.0 –0.9 would represent an “A” grade, >0.9—0.8 a “B” grade, and so on. A rating lower than 0.6 indicates the loss or absence of wetland characteristics for the variable.
FACWet takes the viewpoint that the actual functioning of a wetland cannot be fully determined without intensive, long-term quantitative study. It also acknowledges that quantitative comparison of an assessment wetland with other similar types of wetlands (“reference population”) to determine its relative functional capacity presents practical and theoretical difficulties. Instead, FACWet makes the key assumption that if a wetland has not been altered by humans then, regardless of the wetland type, it is performing its functions at natural rates and capacities.
FACWet uses evaluation of ecological stressors to gauge the departure of a assessment wetland from its natural condition and level of functioning. Here, stressors are defined as direct human-induced alterations of the state variables. No data is collected during a typical FACWet evaluation. Instead, evaluators use their best professional judgment guided by the best evidence available to gauge the effects of stressors. Rating is calibrated by scoring guidelines, which lend consistency to the scoring of variable impairment. If more exact information on impairment is required, FACWet can be used to structure more intensive, quantitative investigations.
In FACWet, variables exhibiting primary control over a given function are combined in a simple algorithm to rate the capacity of that function relative to its natural state. These algorithms are termed “Functional Capacity Indices” (FCIs). Each FCI is unique and includes a subset of the total number of variables and weights for each variable which represent the relative importance of the variable in controlling the function. FACWet includes FCIs for the following seven key wetland functions:
· Support of Characteristic Wildlife Habitat
· Support of Characteristic Fish/aquatic Habitat
· Flood Attenuation
· Short– and Long-term water storage
· Water Quality Maintenance
· Sediment Retention/Shoreline or Bank Stabilization
· Production/Food Web Support
FACWet rates the character and capacity of these functions relative to their reference standard state. It does not rate the societal value of any given function. While fundamentally important, particularly to the Clean Water Act program, the value of a given function is case dependent and highly subjective. For instance, a land developer might deem Support of Wildlife Habitat of relatively low value as compared to the societal benefit of constructing a shopping center, while a conservation-centered group may take an opposite view point. FACWet leaves discussion of the societal value of functions up to permit applicants and regulatory agencies and to the public comment mechanism which was promulgated for this very purpose.
FACWet was designed to target the needs of regulatory agencies in administration of the Clean Water Act in Colorado. In particular, FACWet is intended to be used to rate the functional condition of wetlands during the Section 404 permitting process, before a mitigation action (e.g., restoration or enhancement of wetland habitat), or after its completion. It is also intended to help formulate mitigation plans by cataloging key stressors which could be alleviated by site improvements, and, importantly identifying those stressors which cannot be practically addressed (e.g., an upstream dam). Through such analyses realistic mitigation goals can be outlined and the potential degree of site improvement can be modeled. While geared towards wetland regulation, FACWet can be used in a number of different applications. Its rapid format and inventory of stressors makes it particularly useful for extensive regional surveys of wetland condition and analysis of the impacts impairing wetland health, for example.
It is important to note that, by itself, FACWet does not provide the necessary detail to take the place of a post-build monitoring program; however, it can be used to determine whether the basic, agreed-upon goals of a mitigation project have been met (e.g., a ditch has been filled, site grading performed, water flow re-established, etc.), and it can be used to structure monitoring programs. Basically, FACWet is used to describe “what’s wrong” with a wetland, how it can be fixed, and the probable outcome of site improvements. Once site improvements have been executed, it can then be used to catalog the specific nature of improvements. Quantitative monitoring based on the FACWet results can then be used to demonstrate the actual efficacy of remedial measures and determine whether specific success criteria have been met.
The FuncTional Assessment of Colorado Wetlands (FACWet) Methodology