Analysis of the hydrologic conditions during the flood event occurred in Mandra, Greece, on November 2017

On November 15, 2017 a flash flood struck West Attica with intense effects in the settlement of Mandra, causing human losses as well as extensive material damages. The aim of this work is to examine this flood event from a hydrological perspective in order to highlight the diversity of estimations after considering different methods for the peak discharge determination at the outlet of two small watersheds that correspond to Agia Ekaterini and Soures streams (upstream Mandra settlement). Firstly, discharge is calculated using the rational method, considering the Giandotti, SCS, Kirpich and Passini equations for the time of concentration and a return period equal to 100 years, as, according to the available IDF for the region, the rainfall intensity recorded is close to this return period. Furthermore, the watersheds' unit hydrographs are calculated using the GIS-based time-area diagram approach, to compose the flood hydrographs and to compare peak discharge values. Finally, different scenarios regarding hydrological losses are applied to further demonstrate their impact on estimations