Envelope curves for extreme flood events in northwestern and western Greece

Abstract

Abstract Maximum flood experience in the northwestern and western regions of Greece can be depicted in graphs on which the maximum observed peak discharges are plotted against drainage areas. The peak discharges are found to be power functions of the drainage areas, and the curves enveloping the plotted points differ from region to region according to the climatic regime. The exponents of the Greek envelope curves are in the range of values of the exponents of yearly floodflow-drainage area envelope curves developed in conterminous U.S. basins, but the former curves' constants are much lower than the latter. When the peak discharges are plotted against a morphoclimatic index, which is the product of the expected storm duration by the maximum observed average storm intensity for this duration by the area of the drainage basin, a single linear envelope curve is drawn for both regions that explains 95% of the regional variation in the dependent variable. This curve is free from several drawbacks of floodflow-drainage area envelope curves, i.e. it does not need the determination of region boundaries, etc. The developed envelope curves can predict peak discharges at certain probability levels for ungauged basins of the area and can be used in specific engineering applications.