Equations for estimating the magnitude and frequency of floods at ungaged sites on streams in Alaska and conterminous basins of Canada were developed using multipleregression analyses of basin climatic and physical characteristics and peak-flow statistics from 260 gaged locations in Alaska and 72 gaged locations in Canada. Methods are presented for estimating flood magnitude and frequency at sites on gaged streams. Flood-frequency data based on observed peaks and basin physical and climatic characteristics are given for 332 gaged locations on streams with natural flow. The State of Alaska and conterminous basins of Canada were divided into five flood-frequency areas having similar flood characteristics on the basis of statistical cluster analyses and regional regression analyses. Generalized skew coefficients were determined for each of the five flood-frequency areas using at-site unbiased skew coefficients computed for 82 stations in Alaska having 22 or more annual peaks through the 1987 water year and 31 stations in Canada having 22 or more annual peaks through the 1984 calendar year. A set of equations for estimating peak discharge having recurrence intervals of 2,5,10,25, 50,100, 200, and 500 years was developed for each flood-frequency area. Significant basin characteristics in the equations are drainage area, mean annual precipitation, percentage of lakes and ponds, mean minimum January temperature, mean basin elevation, and percentage of forest. Drainage basin sizes range from 1.02 to 321,000 square miles. Average standard errors of prediction for the equations range from 26 to 77 percent.
A regionalized mean annual precipitation map for the climatic normal period of 1951-80 was developed for Alaska west of longitude 141° and modified from published maps for southeastern Alaska and conterminous basins of Canada. Maximum known floods at 722 sites in Alaska and conterminous basins of Canada are tabulated.
