Abstract
It may be quite reasonable to consider that the generation in severe hydrologic events of basic elements in water-works design is an uncertain quantity swayed by many physical and probable elements in nature. Therefore, under present conditions, water-works design must be framed on various assumptions. In this paper, the authors assume that the probability of generation in severe hydrologic events has Poisson distribution, and study on making use of Bayes' theorem in regard to the recurrence intervals of large severe hydrologic events like the heavy rain etc., further, try evaluations of the security or the risk on water-works design.
