Estimation of the degree of extremality of high-water flows in selected rivers in Poland in 1971-2006

The paper presents the results of estimation and comparison of risk of extreme floods on rivers of various hydrological regime. The hypothesis that extreme events occur with the same frequency in all rivers was rejected. The limit between extreme and common floods on 30 rivers from different geographical regions of Poland was defined on the basis of standardized flow-duration curve in 1971-2006. These analyses resulted in designing five curve groups. Four measures of flood magnitude have been proposed. The time distribution of extreme events during the last decades was estimated for the most dynamic rivers.