Flood susceptibility analysis on urbanized alluvial fans in the northeast of Uludağ mass

Alluvial fans are one of the most preferred morphological units in many places worldwide, especially in terms of settlement and agricultural activities. However, due to the morphological features of alluvial fans and feeder basins, flooding occurs frequently. This study investigates the flood generation potential of alluvial fans and feeder basins located on the north-northeast slopes of Uludağ, the highest mass of the Marmara Region, where urban settlement is intense. The research employs the 5m resolution Digital Elevation Model (DEM) data obtained from 1:5000 scale plans, different dated Corine land use data, high-resolution satellite images, and findings from field studies. Drainage basins and alluvial fan areas are produced using 5m resolution Digital Elevation Model (DEM) data. Vector data-based morphometric analyses (linear, areal, and relief) are applied to the drainage basins, and the analysis results are discussed in terms of flood vulnerability. Basin/fan morphometric analysis is well-known and widely accepted among the methods used in alluvial fan area studies. In this context, the morphometric parameters of alluvial fans, such as area, length, slope, and flow process, examine their morphometric relations with the drainage basins behind them. Apart from morphometric methods in alluvial fan areas, the role of human-induced land-use characteristics, the direction of the highways on the fan surface, the presence of bridges and the effects of improper or insufficient stream improvements in drainage areas are discussed in terms of floods. In the research findings, Gökdere, Akçaalan, Devrengeç, Çukuryayla, Kaplıkaya, Erikli, Kocabalıklı, Küçükbalıklı, Çardakseki, Değirmenönü and Deliçay drainage basins from west to east in the north of Uludağ mass has been determined. In front of these basins, eight alluvial fan systems, four of which are alluvial fans and four of which are alluvial cones, are determined as spatially different. In terms of flood vulnerability of the basins feeding the fans, Deliçay and Gökdere were found as high, Kaplıkaya, Çardakseki, Akçaalan, Devrengeç, Küçükbalıklı, Değirmenönü, Kocabalıklı, Erikli and Çukuryayla basins as medium susceptible. In response to the flooding potential of these basins, Erikli, Devrengeç and Çukuryayla are listed as very high, Kaplıkaya, Gökdere and Akçaalan as high, Balıklıdere and Deliçay as medium-vulnerable alluvial fans. Kaplıkaya basin and its fan have the highest flood generation capacity.