Estimating relative wetland values for regional planning

A numeric method is described for establishing the relative values of wetlands in regional planning. The method combines qualitative understanding of how local wetlands function with assessments of their regional values. The method, called the IVA (Indicator Value Assessment), is a rapid assessment method based on the assumption that wetlands having specific environmental indicators perform a wetland function better than those that do not. The importance of an indicator in the performance of a function is represented numerically. First, 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. Performance scores are normalized on a scale of 0–100, relative to the wetland having the highest performance score in the planning region. Values for wetlands are then quantified by multiplying the area of the wetland by its performance score and by a rank score representing the relative social importance of that function. The performance and value scores can then be used to assess possible impacts from different development scenarios, identify compensation needs within a planning region, and assess the potential of different wetlands for enhancement. The IVA method is being tested and used in three wetland management plans in small watersheds: the Hackensack Meadowlands (New Jersey) Special Area Management Plan (SAMP), the Mill Creek (Washington State) SAMP, and the Snohomish Estuary Plan (Washington State).