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L-moment diagrams are constructed for annual minimum, average, and maximum streamflows at more than 1,455 river basins in the United States. Goodness-of-fit comparisons reveal that the generalized extreme value (GEV), three-parameter lognormal (LN3) and the log Pearson Type III (LP3) distributions provide good approximations to the distribution of annual maximum flood flows. These results are consistent with other L-moment studies. A World Meteorological Organization survey of 54 agencies in 28 countries reveals that the LN3 distribution is not a standard in any country, GEV is a standard in one country, and LP3 is a standard in seven countries. The time is ripe for agencies and countries to reevaluate their standards with respect to the choice of a suitable model for flood frequency analysis. L-moment diagrams also reveal that among numerous alternatives, the Pearson Type III (P3) distribution provides the best fit to both annual minimum and annual average streamflows.
Vogel et al. (Mon,) studied this question.