Flood risk assessment in the most heavily urbanized area of Greece, the case study of Kifissos river basin in Athens.

Urban areas characterized by high density of population and infrastructure can be extremely prone to floods. The flood modeling and management of these areas present high complexity due to their distinctive features. Therefore, advanced methodologies for an accurate assessment of urban flood processes need to be developed. This study presents the methodology and the results for flood risk assessment at high spatial resolution of the Kifissos river basin in Greece. This is the largest one of the five flood-stricken river basins in the region of Attica that are studied in the framework of the Programming Agreement between the Prefecture of Attica and the Operational Unit BEYOND Centre of EO Research and Satellite Remote Sensing of the Institute of Astronomy, Astrophysics, Space Applications & Remote Sensing (IAASARS) of the National Observatory of Athens (NOA), in cooperation with the Research Group ITIA of the Department of Water Resources and Environmental Engineering of the School of Civil Engineering of the National Technical University of Athens (NTUA). Kifissos basin is highly urbanized (80% of the river basin), has been affected by forest fires over the last years, and contains a complex hydraulic network (60% of the total river network is artificial). Thus, the modelling of a river basin with many hydraulic works is a significant challenge, which needs to be addressed to simulate the current situation of the river flow and support the expanding constructions. HEC-RAS 6.4.1 hydraulic model is used for the flood hazard assessment for 50, 100 and 1000 years return period using earth observation, as well as spatial and field data. The vulnerability is estimated by combining different disaster resilience parameters, such as population density, population age and building type, applying different weights. Flood risk is assessed on the impact of hazard, total vulnerability, and economic exposure. Alongside the model’s results including the inundated areas, the flow depths and consequently the flood risk, critical points identified from the field visits are also presented and classified in risk priority. Thus, the presented results are cross-checked with the high-risk areas pointed out from the authorities as well as the civilians’ calls to the Fire Brigade for water pumping over the last 15 years.