Regional regression equations based on channel-width characteristics to estimate peak-flow frequencies at ungaged sites in Montana using peak-flow frequency data through water year 2011

First posted August 19, 2021 For additional information, contact: Director, Wyoming-Montana Water Science Center U.S. Geological Survey3162 Bozeman Avenue Helena, MT 59601 The Survey, in cooperation with the Montana Department of Transportation, developed regression equations based on channel width to estimate peak-flow frequencies at ungaged sites Montana. are data streamgages through September 2011 (end water year 2011), and widths measured field from aerial photographs.Active-channel bankfull (channel widths) were 64 across 2017. Channel also near 515 photographs. These new channel-width data, along more than 438 historical measurements, published a separate release.Regression using generalized least squares or weighted regression. can be used (peak-flow magnitudes associated annual exceedance probabilities 66.7, 50, 42.9, 20, 10, 4, 2, 1, 0.5, 0.2 percent) each eight hydrologic regions Methods presented for weighting estimates basin characteristics. technique reduce standard error prediction relative that obtained single method. Several example problems covering range estimation scenarios included.