A particular comparison of annual maxima and partial duration series methods of flood frequency prediction

A method for comparing the statistical efficiency of the estimate of the T year flood Q (T) by two different methods is described. On the basis of commonly used assumptions it is shown that for return periods greater than about T = 10 years the annual exceedance series estimate of Q (T) has larger sampling variance than the annual maxima series estimate. It is shown that for the same range of return periods the partial duration series estimate of Q (T) has smaller sampling variance than the annual maxima series estimate only if the partial duration series contains at least 1.65 N items, where N is the number of years of record.