The Log Pearson type 3 distribution and its application in hydrology

A mathematical and statistical study which shows the flexibility and limitations of the log Pearson type 3 distribution is carried out. The results obtained indicate the various forms of density function and relationships that exist between distribution parameters and moments, coefficient of variation, and coefficient of skewness. The method of fitting proposed by the Hydrology Committee of the Water Resources Council is compared with a new method which instead of using moments of the logarithmic values retains the moments of the original data. In the case of events with a large return period the results obtained by the two methods may deviate appreciably, and because in the proposed method the same weight is given to each of the observed values, it will result in a better fit of the data.