Seasonal design floods and flood control water levels based on Copula

The triviriate asymmetric Frank Copula is proposed to describe joint distribution of seasonal flood with Pearson Type-Ⅲ distribution margins.When joint return period equals flood prevention standard,the relationship between frequencies of seasonal flood and flood prevention standard is derived;and the inconsistent problem mentioned above is solved.This approach provides a new way to optimize the seasonal design floods and FCWLs.