Primary purpose
To assess wetland functions in the 404 Regulatory Program as well as other regulatory, planning, and management situations.
Expertise needed
Interdisciplinary team of experts required during development phase. Application phase should be done by individual(s) who have personal knowledge and field experience with the regional wetland subclass under consideration.
Applicable habitat types
All wetland types in the United States; however, not all assessment models are developed.
Categories assessed
Variety of wetland functions, the list of which depends upon the wetland regional subclass. Includes functions related to hydrologic processes, biogeochemical processes, and habitat.
Procedure
There are two main phases: development and application. During the development phase an interdisciplinary team of experts (A-team) develops a guidebook with models for assessing functions of wetlands in a regional subclass. The application phase consists of applying the models to an actual project following three steps: characterization; assessment; and analysis. The user(s) visits a wetland assessment area (WAA), or reviews plans for predicted future conditions, and completes data sheets that (a) identify the individual model variables, (b) list direct or indirect measures of model variables, (c) assign a subindex (scale 0.0-1.0) to conditions for each variable, and (d) include the equation for calculating the functional capacity index (FCI). The functional capacity units (FCUs) are also calculated for each function and all results are analyzed.
Key Terminology
Functional capacity: the rate or magnitude at which a wetland ecosystem performs a function. Functional capacity is dictated by characteristics of the wetland ecosystem and the surrounding landscape, and interaction between the two.
Functional capacity index (FCI): an index of the capacity of a wetland to perform a function relative to other wetlands within a regional wetland subclass in a reference domain. An index of 1.0 indicates the wetland performs a function at the highest sustainable functional capacity, the level equivalent to a wetland under reference standard conditions in a reference domain. An index of 0.0 indicates the wetland does not perform the function at a measurable level, and will not recover the capacity to perform the function through natural processes.
Functional capacity units (FCUs): measure of functional capacity incorporating size of the wetland area (FCU = FCI x size of wetland assessment area).
Indicator: observable characteristics that correspond to identifiable conditions in a wetland or the surrounding landscape.
Red flag features: features of a wetland or the surrounding landscape to which special recognition or protection is assigned on the basis of objective criteria. The recognition or protection may occur at a Federal, State, regional, or local level and may be official or unofficial.
Contact Persons
R. Daniel Smith or Ellis J. (Buddy) Clairain, Jr., U.S. Army Corps of Engineers, Waterways Experiment Station, 3909 Halls Ferry Road, Vicksburg, MS 39180-6199
D. Smith: phone: (601) 634-2718; fax: (601) 634-4016; e-mail: Ronald.D.Smith@erdc.usace.army.mil.
E. Clairain: phone: (601) 634-3774; fax: (601) 634-4016; e-mail: Ellis.J.Clairain@erdc.usace.army.mil.
Information also available at Web site: www.wes.army.mil/el/wetlands/gdbks.html
Reference domain: the geographic area from which reference wetlands are selected. A reference domain may or may not include the entire geographic area in which a regional wetland subclass occurs.
Reference standards: conditions exhibited by a group of reference wetlands that correspond to the highest level of functioning (highest, sustainable level of functioning) across the suite of functions performed by the regional subclass. The highest level of functional capacity is assigned an index value of 1.0 by definition.
Reference wetlands: wetland sites that encompass the variability of a regional wetland subclass in a reference domain. Reference wetlands are used to establish the range of conditions for construction and calibration of functional indices and establish reference standards.
Regional guide book: a report summarizing the characteristics of a specific regional subclass and the assessment models prepared during the development phase.
Variable: an attribute or characteristic of a wetland ecosystem or the surrounding landscape that influences the capacity of a wetland to perform a function.
Wetland functions: the normal activities or actions that occur in wetland ecosystems, or simply, the things that wetlands do.
Output
Measure of functional capacity of a site relative to wetlands from the same regional wetland subclass.
Estimated time to assess 1 acre site
Total 1-2 hours per wetland assessment area (WAA) (if models are available)
1-2 hours: Characterization (step 1), assessment (step 2), and analysis (step 3).
Total 321-322 hours (if models must be developed)
320 hours [months of work]: Development phase.
1-2 hours per WAA: Characterization (step 1), assessment (step 2), and analysis (step 3).
Comparison of habitat types
Can directly compare wetlands within the same regional subclass (e.g., vernal pools of California). Cannot directly compare wetlands from different subclasses (e.g., closed depression wetland and upper perennial riverine wetland within same region) or different regions. However, results from assessing different regional subclasses can be used to aid in decisions.
Use as guide to design
The HGM Approach assessment models can be used as a guide to design. Users can refer to the model variables to determine which conditions increase or decrease functional capacity. Functional capacity for the "retain particulates" function is increased when the wetland is designed to have an overbank flood recurrence interval of 1 yr (variable Vfreq). Each variable provides information on conditions that should be avoided. For example, to have a capacity to retain particulates, the ratio of floodplain width to channel width must be > 1 (variable Vstore). Also, the information in the HGM models is useful because it provides design criteria with explicit measurements (e.g., ratio of floodplain width to channel width >55). Finally, not all of the models or variables may be useful. For example, a variable that measures presence or diversity of fauna (e.g., distribution and abundance of invertebrates) cannot be incorporated into the design because the presence of most fauna usually cannot be controlled.
Related procedures
There are modified versions being used which have not been accepted by the US Army Corps of Engineers (COE). Most of these are "project specific" and do not include complete data sets as required for COE approval (Pers. comm.: C. Charles and E. Clairain, USCOE, July 14, 1998). The Natural Resources Conservation Service (NRCS) is developing Interim HGM models for use pursuant to the 1996 Farm Bill (see separate review). The Interim HGM models are based on HGM principles, but contain little reference data. NRCS has agreed to collect data for model verification and validation, and to complete development of regional guidebooks. The following methods are distinct from the HGM Approach, but include HGM Approach concepts and/or terminology in varying degrees: WAFAM (Hruby et al. 1998), MNRAM (MBWSR 1997), EPW (Bartoldus et al. 1995), the MDE Method (Fugro East Inc. 1995), and the Rapid Assessment Procedure (Magee 1998).
Extent of use/field testing
To date, draft regional guidebooks that are approved by the US Army Corps of Engineers have been completed for Western Kentucky (Ainslie et al. 1998) and the prairie potholes (Hauer et al. 1998). The prairie pothole models have been used frequently on a variety of projects (e.g., highway, agriculture, small routine permit projects, Devil’s Lakes dewatering in ND). The Western Kentucky models have been used on a large mining ADID (Advanced Identification) project.
Proposed future revisions
There a no plans to revise the concept of the HGM Approach. Models for individual regional wetland subclasses are being prepared and will continue to be prepared as dictated by the needs and funding. Models are first published in draft regional guidebooks and released for a two year period during which time end-users are invited to comment. Thereafter, the final regional guidebook is published and reviewed every five years.
Key References
Smith, R.D., A. Ammann, C. Bartoldus, and M.M. Brinson. 1995. An Approach for Assessing Wetland Functions Using Hydrogeomorphic Classification, Reference Wetlands, and Functional Indices. Wetlands Research Program Technical Report WRP-DE-9. U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. 88 pp.
Ainslie, W.B., R.D. Smith, B.A. Pruitt, T.H. Roberts, E.J. Sparks, L.W. West, G.L. Godshalk, and M.V. Miller. 1998. A Regional Guidebook for Assessing the Functions of Low Gradient Riverine Wetlands in Western Kentucky (Draft). Wetlands Research Program Technical Report WRP-DE- . U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. 203 pp. ppen.
Brinson, M.M. 1993. A Hydrogeomorphic Classification for Wetlands. Wetlands Research Program Technical Report WRP-DE-4. U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS. 79 pp. ppen.
Brinson, M.M., R. Hauer, L.C. Lee, W.L. Nutter, R. Rheinhardt, R.D. Smith, and D.F. Whigham. 1996. Guidebook for Application of Hydrogeomorphic Assessment to Riverine Wetlands (Operational Draft). Wetlands Research Program Technical Report WRP-DE-11. U.S. Army Corps of Engineers, Waterways Experiment Station, Vicksburg, MS.
U.S. Army Corps of Engineers. 1997. National action plan to implement the hydrogeomorphic approach to assessing wetland functions. Federal Register 62(119):33607-33620.