Risk estimation in partial duration series

The estimation of design floods is, in practice, often based on small samples of data, which may cause a severe uncertainty. For a particular version of the partial duration series (exponentially distributed exceedances and Poissonian occurrence times) the distribution of the T ‐year design estimate is derived along with the distribution of R T ; defined as the true risk of exceeding within a given disposal period. For a fixed flood level the distributions of the return period estimator and the estimator of the risk in lifetime are also presented. Analytical closed‐form expressions for mean value and standard deviation are derived for these variables, except for , which does not possess moments. The concept of “expected risk” is introduced, and an analytical expression describing this property is derived. A risk‐based design technique, which is essentially different from the traditional procedure, is presented, and its applicability is verified using Monte Carlo simulation.