Tara Williams-Sether Nancy A. Barth Katherine J. Chase Mark A. Cedar Face Seth A. Siefken 2025 <p>The U.S. Geological Survey, in cooperation with the Montana Department of Natural Resources and Conservation, North Dakota Department of Water Resources, South Dakota Department of Transportation, and the Wyoming Water Development Office, has developed standard methods of peak-flow frequency analysis for studies in Montana, North Dakota, South Dakota, and Wyoming. These methods describe the implementation of national flood frequency guidelines described in Bulletin 17C (<a data-mce-href="https://doi.org/10.3133/tm4B5" href="https://doi.org/10.3133/tm4B5">https://doi.org/10.3133/tm4B5</a>) for the four States and deviations from Bulletin 17C standard procedures to accommodate unusual hydrologic conditions. A U.S. Geological Survey data release accompanying this report (<a data-mce-href="https://doi.org/10.5066/P1WHRK8H" href="https://doi.org/10.5066/P1WHRK8H">https://doi.org/10.5066/P1WHRK8H</a>) provides example peak-flow frequency analyses for selected streamgages in the study area. The methods described in this report can be used to publish similar data releases for other streamgages in the study area.</p> application/pdf 10.3133/sir20255019 en U.S. Geological Survey Methods for peak-flow frequency analysis for streamgages in or near Montana, North Dakota, South Dakota, and Wyoming reports