Flood Susceptibility Mapping for Ankara Using Modified Analytical Hierarchy Process (M-AHP)

Abstract

Many natural disasters occur in the world and affect both the economies of countries and people’s lives. These disasters can happen in the forms of earthquakes, landslides, tsunamis, droughts, floods, etc., and many disaster events occur in Turkey as well. Natural hazard susceptibility maps, which show the spatial probability distribution of the hazards are needed for land use planning and disaster mitigation purposes. In this thesis, flood susceptibility map production is aimed for dense residential areas in Ankara by using the Modified Analytic Hierarchy Process (M-AHP) method. The method allows sophisticated decision making based on expert opinions. The satellite images, data obtained from the TopoVT geodatabase of General Directorate of Mapping (in Turkish Harita Genel Müdürlüğü - HGM), Ankara, and the lithology data obtained from General Directorate of Mineral Research and Exploration (in Turkish Maden Tetkik ve Arama Genel Müdürlüğü - MTA), Ankara, were used for pre-processing prior to the expert based decision making. Freely available Landsat satellite imagery were employed in a supervised classification process to produce LULC map of the area. The classes of the LULC map were determined as industrial areas, urban, roads, water areas, green fields and barren lands. The geodata obtained from HGM involve both vector and raster datasets. The vector data taken from the TopoVT database of HGM include the hydrological data (e.g. rivers) and the contour lines. A Digital Terrain Model (DTM) was produced by using the contour lines. Topographic derivatives such as flow accumulation, slope, topographic wetness index (TWI) and distance to dry and permanent rivers were computed from the DTM. Raster data obtained from HGM include aerial photogrammetric images of 2008 and 2015. Orthophotos and digital surface models (DSM) of both years were produced from these images. Lithology data were obtained from Earth Science Data Portal of MTA. This dataset was transformed to raster format to be used in the decision making process as well. After the preprocessing, parameter scoring (weighting) was completed by the expert to perform the M-AHP procedure. In the scoring process, each parameter was classified and scored according to the effect of each class on the flood sensitivity. Furthermore, five decision points; i.e. very low, low, moderate, high, and very high, were specified for flood susceptibility map production. These decision points show whether the related area is prone to flood. After these operations, M-AHP process was completed and the flood susceptibility maps of year 2008 and year 2015 were produced. For 3D visualization of the results, the output flood susceptibility map was draped on the DSM. Thus, the flood susceptibility models for both years were produced and compared visually. The results show that the employed data and methods are suitable for the production of flood susceptibility maps at regional scale.