Predicting the mean annual flood and flood quantiles for ungauged catchments in Greece

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Abstract
The spatial variation of the mean annual flood of both mean daily and instantaneous extremes and of the parameters of the Extreme Value Type 1 (EV1) distribution for catchments in the northwest and west regions of Greece are significantly explained in terms of physiographic and climatological characteristics of the catchments by using multiple regression techniques. The catchment characteristics used in the study are the following: drainage area, mean annual areal precipitation, stream frequency, main stream slope and length, intensity of the one-day rainfall of five-year return period, and a soil type index. The EV1 distribution has been found to describe adequately the annual frequency distributions of the daily and of the standardised by-their-mean-value daily extremes of the catchments. Based on the regional models for the parameters of the distribution, annual flood frequency curves, and thus flood quantiles of the assumed distribution, can be derived. The developed regional models are successfully used in predicting with satisfactory accuracy the mean annual floods and flood quantiles, needed in hydrological design, for ungauged catchments within the region studied.