These Regional SDAMs were developed for use in all or part of the states of Arizona, California, Colorado, Illinois, Iowa, Kansas, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, Wisconsin, and Wyoming by the Corps and the EPA (Figure 1). These methods result from a literature review and multi-year field study conducted at nearly 700 stream reaches across the range of hydrologic landscapes of the Arid West, Western Mountains and Great Plains. Developed through statistical analyses of the field data, the Regional SDAMs provide a data-driven approach using reliable indicators to determine streamflow duration class at the reach scale. The agencies are making these final Regional SDAMs available for public use.  This follows completion of a more than one year preliminary implementation and comment period on beta methods to inform development of the final Regional SDAMs.