Spreadsheets to Estimate Compensation Ratios Based on HGM AssessmentsThe two spreadsheets provided here can be used to help evaluate the impacts of wetland projects and estimate mitigation requirements. The spreadsheets were developed by Frank Hanrahan based on concepts presented by the U. S. Fish and Wildlife Service (1980) and King and Adler (1992). The first was written in 1999 using Corel Quattro Pro software and the second in 2001 using Microsoft Excel. The spreadsheets use the results of an assessment of wetland functions based on the Hydrogeomorphic (HGM) Approach at an impacted site to calculate mitigation requirements at a restored or constructed wetland site. For each function, the spreadsheets calculate a Compensation Ratio or Functional Equivalency Ratio (i.e., the number of acres of mitigation site required per acre of original wetland impacted to achieve equivalency between loss and gain of function). These ratios are based on the functional capacity index (FCI) determined at the original wetland and the predicted FCI that will be achieved over time at the restored/created wetland. In addition, the spreadsheets calculate a weighted average compensation ratio across all functions (the ratio with trade-offs) weighted by an index of the relative importance of each function in the study area or region. Thus, a function whose relative importance is 2 has twice the weight in a trade-off decision as a function whose relative importance is 1. At the present time, judgments about the relative importance of wetland functions are necessarily subjective. Options for establishing relative importance indices include (1) negotiation and consensus of concerned public agencies and stakeholders in a project, (2) soliciting opinions from an impartial panel by a procedure such as the Delphi technique, and (3) using a procedure that relates wetland functions to the flow of human services and benefits that accrue from those functions over time (e.g., King et al. 2000). If desired, all relative importance indices can be set to one (i.e., functions are of equal value). However, averaging across functions, even if they are equally valued, implies that unlimited trade-offs among functions are acceptable in developing a compensation ratio. Users may choose to ignore the ratio with trade-offs altogether and focus instead on the individual compensation ratios for each function. A number of assumptions have been made to simplify the applications and to allow presentation of the spreadsheet template on a single page. If these assumptions do not match the circumstances of a particular study, the investigator may wish to use the more complex but flexible Expert HGM (EXHGM) software being developed as part of the Integrated Bio-Economic Planning System (IBEPS) for use by Corps of Engineers District offices. Some of the important features of both spreadsheets include:
Notes on the Quattro Pro Version As a check on the input data and to help understand the results of the analysis more clearly, the Quattro Pro version provides optional graphical output. An example graph with explanatory notes appears below the Outputs table of the spreadsheet, starting in row 100. Graphs requested by the user appear below the example graph. Graphical output is triggered by keying Ctrl-Shift-A for Function A, Ctrl-Shift-B for Function B, etc., and must be updated the same way if you make changes in the inputs table. The graphs display the following information over the time horizon: (1) yearly FCI at the impacted site, (2) yearly FCI at the mitigation site, (3) yearly acre-for-acre surplus or deficit in FCI (i.e., the difference between (1) and (2) above, standardized to an initial level of zero), (4) yearly surplus or deficit at the equivalency acreage ratio for that function, (5) the "present value" (PV_{0}) of that surplus or deficit at the specified discount rate (this is the same as (4) if the discount rate = 0), and (6) the cumulative present value of the surplus or deficit over the time horizon. The last value should approach zero by the end of the time horizon, indicating that the expected benefits of the mitigation will balance the impacts by the end of the period of analysis. Caution: Notes on the Excel Version Reporting Problems References King, D. M., Wainger, L. A., Bartoldus, C. C., and Wakeley, J. S. (2000). "Expanding Wetland Assessment Procedures: Linking Indices of Wetland Function with Services and Values," Technical Report ERDC/EL TR-00-17, U.S. Army Engineer Research and Development Center, Vicksburg, MS. U. S. Fish and Wildlife Service. (1980). "Habitat Evaluation Procedures", Ecological Services Manual 102, Washington, DC. Web Date: October 1997 |