Primary purpose
To provide separate estimates of the performance of socially important functions within a wetland as well as an estimate of the relative value of that wetland within a planning region. May be used to (a) assess possible impacts from different development scenarios, (b) identify compensation needs within a planning region, and (c) assess the potential of different wetlands for enhancement.
Expertise needed
A group of experts knowledgeable of the wetlands in the planning region or watershed.
Applicable habitat types
All wetlands types in the United States; however, not all assessment models are developed.
Categories assessed
A variety of wetland functions and values, the list of which depends upon the wetland study area (watershed or planning area). Would likely include functions related to hydrologic processes, biogeochemical processes, habitat, and social issues.
Procedure
IVA involves six steps accomplished by consensus among local groups and agencies with permit or other legal authority over local wetlands. The steps are (a) identify wetland functions, (b) identify indicators for each function, (c) assign scores to indicators, (d) estimate performance score for each function (scale 0-100), (e) establish the relative social importance of functions, and (f) estimate value of wetlands.
Key Terminology
Indicators: variables that have a documented or hypothesized association with particular wetland functions. There are three types:
Additive indicators: associated with an incremental increase in performance; scored as positive integers (i.e., 1,3,9) and summed.
Fractional indicators: associated with decreased in performance; scored as numbers less than "1" and also used to multiply the sum (of additive indicators).
Multiplicative indicators: associated with significant increased in performance; scored as numbers greater than "1" and used to multiply the sum (of additive indicators).
Performance score (for a wetland function): a score bounded by 0 and 100 estimating the relative performance of a function, where 100 represents the highest performance of a wetland in the planning region. A performance score for a wetland is calculated by developing a numeric model for each function based on the importance scores assigned to the indicators.
Relative social importance (of functions): social importance of a function as determined by a group of all parties interested in the wetland resources of the planning area. Importance may be done by (a) ranking and assigning a numeric score, or (b) combining functions into function groups.
Value score (of a wetland): the relative social importance assigned a function reported as "acre-points" or "hectare-points" (value = performance score x area x social importance of function).
Output
Measures function performance, relative social importance, and value of a site relative to wetlands within the same planning region or watershed.
Estimate time to assess 1 acre site
Total 1-4 hours per site (if models are available)
1-4 hours: Estimate Value Score (step 6)
Total 41-68 hours per planning region or watershed (if models must be developed)
24-40 hours: Identify wetland functions (step 1), identify indicators for each function (step 2), assign scores to indicators (step 3), and estimate performance score (step 4).
16-24 hours: Establish Relative Social Importance (step 5)
1-4 hours per site: Estimate Value Score (step 6)
Contact person
Thomas Hruby, WA State Dept. of Ecology, P.O. Box 47600, Olympia, WA 98504 phone: (360) 407-7274; fax: (360) 407-6535; e-mail: thru461@ecy.wa.gov
Comparison of habitat types
Can directly compare wetlands within same defined geographic area (e.g., watershed, planning area). The wetlands can be from the same or from different wetland type or class.
Use as guide to design
Only a small example of the models is published (Hruby 1996) and the description of indicators is abbreviated; therefore, if is difficult to determine whether the models should be used as a guide to design. It appears that IVA should not be used as a guide to design; however, individual variables may provide useful information. It is not the intended purpose for this procedure; therefore, it contains properties that limit its application for this purpose. For example, since IVA indicators are based on WET (Adamus et al. 1987), the threshold values of many variables may not be validated. Some variables may provide useful information. Users can refer to the variables to determine which conditions increase or decrease function or value. This can be translated into design criteria with explicit measurements (e.g., design a wetland with outlet (one third average width). Finally, the design criteria for some variables may be unsuitable and the overall rating of function may be misleading for the reasons given above.
Related procedures
Most of the indicators in IVA are based on predictors from WET (Adamus et al. 1987). Some concepts from IVA have been incorporated into the WAFAM (Hruby et al. 1998).
Extent of use/ field testing
IVA has been used on the Hackensack Meadowlands Special Area Management Plan (SAMP) in New Jersey; Mill Creek SAMP, WA; Snohomish Estuary Plan, WA; and Port of Skagit Wetland Plan (WIN), WA.
Proposed future revisions
None.
Key Reference
Hruby, T., W.R. Cesaneck, and K.E. Miller. 1995. Estimating relative wetland values for regional planning. Wetlands 15(2):93-107.