Application Of The Index-flood Method To TheRegionalization Of Flood Peak Discharges On ThePortugal Mainland

Abstract

The regional analysis of flood peak discharges is an important tool that enables more reliable estimates of flood quantiles at watersheds without or with insufficient flood data. Usually, the flood regional analysis combines two main issues concerning, first, the identification of homogenous regions in terms of flood peak discharges and, second, the establishment of, for each region previously recognized as homogenous, a flood frequency distribution model. One of the most widespread procedures for flood regionalization is the index-flood method. As the main assumption, the method considers that the statistical distribution of the floods within a homogenous region is similar except for a scale parameter or index that reflects the specific local features. The index-flood method was applied to the Portugal mainland, based on the records of annual maximum instantaneous discharges at 120 Portuguese stream gauging stations. As result, six homogenous regions were identified and the models applicable to each region to estimate flood quantiles established. The adopted index-flood was the mean annual flood, that is, the flood having a peak discharge with a return period of 2.33 years. In this paper the general description of the method as well as some of the results achieved for the Portugal mainland are briefly presented.