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Archive

Collection and valuation of information on past historical flash floods


Payrastre Olivier

The results of an investigation on historical floods in four watersheds of the Aude region in France will be presented. Using both, archive documents and field investigations, the discharges of the main historical floods could be estimated for a period ranging from one to two centuries.
The use of this data, in addition to systematic discharge measurements (continuous series of about 30 years in each case) shows that the calibration of the standard Gumbel and EVII statistical distributions is highly modified by using historical data, despite of the poor accuracy of discharge estimations for historical floods. In other words, the historical perspective modifies completely the hydrological risk perception on these watersheds.
In some cases, it is also possible, with a simple test using historical data, to exclude a type of statistical distribution (Gumbel in the presented case) which is not adapted to represent both historical and systematic data samples. Lastly, the historical data gathered highlights important differences in flood intensities among the four studied watersheds, differences that seem not to be explained by variations of the the meteorological hazard only.