‘How would an extreme flood have behaved if flood protection works were built?’ the case of the disastrous flash flood of November 2017 in Mandra, Attica, Greece

ABSTRACT

The flash flood in the town of Mandra, Attica, in 2017 that had a return period equal to approximately T = 150 years was one of the most disastrous floods in Greece. Four years later, flood protection works designed for T = 50 years were built. In this work, we pose the research question ‘How would this disastrous flood have behaved if flood protection works were built?’ To answer this question, we employed the HEC-RAS 1D/2D model, over a detailed DSM, that we calibrated with field measurements to simulate the flood of 2017. We derived the following conclusions: (1) Flooding of the main streets still occurs with 15–25% lower flow velocities and 19–29% lower water depths. (2) The total extent of the inundation areas is reduced by 17%. (3) Works delay flood arrival by approximately 1.5 hour, thus providing the opportunity for an Early Warning System to respond more effectively.

KEYWORDS:

• Flood protection works
• flash floods
• HEC-RAS 1D/2D
• hydrodynamic modelling
• flood arrival times

Acknowledgements

The present work was performed within the framework of the project “National Network on Climate Change and its Impacts (CLIMPACT)” of the General Secretariat of Research and Technology (https://climpact.gr/main/); CLIMPACT is a consortium of 10 partners with more than 200 researchers, who exchange know-how, experience, and suggestions for the adaptation and the mitigation of the impacts of Climate Change on floods, agriculture, tourism, marine environment, and air pollution.

Disclosure statement

No potential conflict of interest was reported by the author(s).