Flood risk assessment using remote sensing and geographical information systems (GIS). An example from Kassandra peninsula, Chalkidiki, Greece

Περίληψη

Floods are natural phenomena and are an integral part of the water cycle. The majority of them are the result of climatic conditions, but are also affected by the geology and geomorphology of the area, topography and hydrology, the water permeability of the soil and the vegetation cover, as well as by all kinds of human activities and structures. However, from the moment that human lives are at risk and significant economic impact is recorded, this natural phenomenon becomes a natural disaster. Flood management is now a key issue at regional and local level around the world, affecting human lives and activities. The majority of floods are unlikely to be fully predicted, but it is feasible to reduce their risks through appropriate management plans and constructions. This study was carried out due to the repeated catastrophic floods that have occured in Kassandra peninsula, Halkidiki, Greece and more specifically in the area of Fourka, causing numerous damages. The main purpose of this study is to evaluate the contribution of remote sensing technology and Geographic Information Systems (GIS) in assessing the susceptibility of this region to flood events. Kassandra is facing anthropogenic floods; human intrventions on streams, the beds of which have been trampled to build houses and hotels or have been converted into roads, are causing flooding after every heavy rainfall. The streams crossing settlements and areas with high touristic development have been intensively modified by humans, as the pressure for real estate development land is growing. In particularly, several areas in Kassandra are facing high risk of extensive flood occurrence, since fires happened in the past and flood protection infrastructure has been seriously damaged.. Such examples are the catastrophic fires in August 2006, which destroyed 60 % of the forested area of Kassandra and the dramatic floods that followed in September 2007. This study concentrates on the construction of a flood susceptibility map, of the study area, by combining vulnerability elements, using the Analytical Hierarchy Process/ AHP (Saaty, 1980). After processing of a digital elevation model (DEM), important secondary data were extracted, such as the slope map, the flow direction and the flow accumulation. Together with additional thematic information (e.g. geological maps, land cover etc.), these led to the final four major factors for creating the flood susceptibility map,i.e. the Topographic wetness index, Lithology, Roughness - Land cover and Vegetation cover index (NDVI). These factors were co-evaluated, in order to produce the final map, which categorizes the area into zones of higher to lower flood susceptibility.