Urban flood hazard assessment in the basin of Athens Metropolitan city, Greece

Flood events have often occurred in the metropolitan urban area of Athens, capital of Greece, causing loss of property and in many cases human lives. In this study a flood hazard assessment model for urban areas is examined. The Kifisos and Ilisos Rivers flowing through the plain of Athens was the case study of the present work. The quantitative analysis of the Kifisos and Ilisos Rivers drainage networks was performed to identify flash-flood prone areas. The major factors affecting urban floods were estimated. The slope angle, elevation, distance from open channel streams, distance from totally covered streams, hydro-lithology and land cover of the study area were used. to evaluate these factors the analytical hierarchical process method was applied in a geographical information system. A sensitivity analysis was made to assess the effect of the various factors on the flood hazard map. Three scenarios were developed to examine the effect of uncertainty of the factors' values to the flood hazard assessment results, leading to the corresponding urban flood hazard assessment maps. The produced map showed that the areas of very high flood hazard are located mostly along the lower reaches of Kifisos and Ilisos Rivers, particularly to the southern and to the western part of the study area. These areas are characterized by lowland morphology, gentle slope, totally covered streams, expansion of impermeable formation and intense urbanization. The uncertainty analysis shows no significant differences on the spatial distribution of the hazard zones. The produced urban flood hazard map proves a satisfactory agreement between the flood hazard zones and the spatial distribution of flood phenomena that have affected the study area in the past 117 years. Furthermore, the comparison between the floodprone areas that were derived from the geomorphological analysis of the drainage networks and the high flood-hazard zones of the final map indicated reliable results and a high accuracy of the proposed methodology.