Palaeoflood discharge estimation using dendrogeomorphic methods, rainfall-runoff and hydraulic modelling—a case study from southern Crete

Abstract

This study represents the first palaeoflood discharge estimation using dendrogeomorphic evidence from two ungauged catchments in southern Crete. Dendrogeomorphological methods, rainfall-runoff and hydraulic modelling were applied to estimate the palaeoflood discharge of the 2000 flood event. We developed two scenarios (QHydraulic, QRR) of peak discharges in the short reaches of the Ilingas and Sfakia catchments. Scenario QRR was based on the results of the uncalibrated rainfall-runoff model HEC-HMS. The calculated discharges were equal to 35.9 m3 s−1 in the Ilingas reach and 7.6 m3 s−1 in the Sfakia reach. The second scenario, QHydraulic was based on the output of the two-dimensional hydraulic model IBER, which was calibrated using six palaeostage indicators obtained during a field survey. The reconstructed discharge for the QHydraulic scenario was equal to 26.3 m3 s−1 in Ilingas and 11.2 m3 s−1 in Sfakia. Deviation (26.7% in Ilingas and 32.1% in Sfakia) between the scenarios were attributed mainly to the uncertainties of in flood reconstruction using the palaeostage indicators and uncalibrated rainfall-runoff model. We further investigated uncertainty in Manning’s roughness coefficient, which caused deviations in peak discharges with the range of these deviations defined within ± 40% in the Ilingas reach and ± 36% in the Sfakia reach.