A practical trial example in flood susceptibility studies: Determination of flood susceptibility in Bozburun Peninsula (Marmaris/Türkiye) basins

Abstract

This study, carried out in the Bozburun Peninsula (Marmaris-Türkiye), which constantly faces the reality of flood disasters, aimed to determine the torrent and flood susceptibility levels on the basis of sub-basins. For this purpose, some hydrological analyses frequently used in geomorphology and hydrology studies were used. An important part of these analyses consists of the calculation of some morphometric indices. The indices preferred and calculated in our study are; bifurcation ratio (B_r), texture ratio (T), drainage density (D_d), basin shape ratio (B_s), relief ratio (R_r), roughness value (Rn), stream accumulation time (T_c), hypsometric integral (H_i) and harmonic slope averages (H_sl) of the first series of streams in each sub-basin. Arc GIS 10.5 package program was used to create and process morphometric indices. While determining the torrent and flood susceptibility of the basins in question, the ranking and scoring of each parametric value on a sub-basin basis was done using a colouring scale in the Microsoft Excel 2010 program. First, the sub-basins were ranked according to their flood generation potential, and then, as 10 sub-basins were selected, susceptibility scores from 1 to 10 were assigned. However, only detecting and scoring the parameters in question may not be sufficient in some cases. Because each parameter will not contribute equally to flood susceptibility. In addition, relying only on expert opinion may lead to a subjective evaluation. The main difference of this study stems from the search for ways to eliminate this problem. In order to overcome these limitations and subjective evaluations, the AHP method, which is a decision-making matrix, was used in the study. In this way, it is thought that a stronger and more objective ranking can be achieved in a quantitative sense. For this purpose, the weight percentage results obtained in AHP were added to the previous scoring as a multiplier. Ultimately, these rankings were reduced to five susceptibility categories -simplified- and mapped. As a result of the analysis, it was determined that the sub-basins in the peninsula, which have a significant population, have high/very high flood susceptibility. Historical floods and field works were used as references to check the results obtained, and it was seen that the results pointed to basins that constantly face floods. Only the selection of these parameters and the extent to which prioritization with AHP will benefit need to be controlled in different regions. However, despite all this, it is thought that this study will be able to provide practical benefit and guidance to relevant researchers and decision makers.