Zur Ermittlung von hydrologischen Bemessungsgrößen an Flussmündungen mit Verfahren der multivariaten Statistik

The design of flood protection structures in the direct reach of river confluences is exceptionally challenging for engineers. This is mainly because commonly applied univariate statistical methods are not valid to derive the hydrological design parameters. In this thesis various aspects are investigated to determine hydrologic and hydraulic parameters for the design of flood protection structures in the direct reach of river confluences to meet safety and economic requirements. First, general aspects influencing statistical analyses of hydrological time series are investigated. Therefore, the influence of different discretisation time spans of discharge time series as well as non-stationarities of the univariate parameters on statistically derived design values are explored. The main focus of the thesis is on estimating design events for flood protection structures in the direct reach of river confluences. A new methodology is introduced for cases where long discharge time series are available at both rivers the main stream and the tributary. The approach uses Copula functions and is based on overlapping quantile-isolines for the derivation of bivariate design events if the variables to be modeled not necessarily occur simultaneously. For river confluences where no discharge time series are available, a general approach is developed to estimate the discharge combinations of both streams in the context of joint occurrence. This thesis provides a significant contribution to the reliable identification of design relevant flood discharges at river confluences.