A GIS MODEL FOR EVALUATING THE IMPACTS OF COAL BED METHANE SURFACE WATER DISCHARGES

A GIS based program, Erosion Potential (EP) Modeler, has been developed to facilitate the calculation of an index that can be used to assess the potential for accelerated channel erosion in response to increased discharges in a channel. In general, EP Modeler was developed to help those responsible for or concerned about watersheds affected by coal bed methane (CBM) development in the Powder River (structural) Basin (PRB), located in northeast Wyoming, where CBM development has been occurring at an increasing rate since about 1990. In particular, EP Modeler was developed to assist Wyoming Department of Environmental Quality personnel formulate appropriate management decisions associated with the National Pollution Discharge Elimination System permitting process. EP Modeler estimates pre- and post-CBM development equilibrium channel widths and reports the percent change in width as an index of the potential for channel erosion. Pre- and post-CBM development channel widths are computed as a function of the bankfull discharge and the sum of bankfull discharge and anticipated CBM product water discharge, respectively. Data from field surveys was used to calibrate EP Modeler and data obtained in the future will be used to verify predictions from EP Modeler. Results from EP Modeler indicate that the potential for accelerated erosion because of CBM development is proportional to basin size and that changes in channel width on the order of one to ten percent could occur in the PRB.