The Flood Risk of the Yeşilırmak Basin (upper course), Turkey

This paper presents the flood potential of the sub-basins, which are located in upper course of the Yeşilırmak River, Tokat Province. This potential was determined by analysing shape indices which have been used for several decades to describe the characteristics and hydrological properties of drainage basins. These indices are Form Factor, Basin Elongation, compactness, circularity Ratio, Lemniscate ratio and shape index. Drainage networks for sub-basins were prepared with a topographic map scaled 1/25000 and 10-m resolution DEM using GIS. The study area was divided into six sub-basins. The shape indices show that six sub-basins have an elongated shape causing low-magnitude peak flood. In spite of a moderate amount of rainfall and elongated shapes, the main problem of this area is that it has been subjected to flood since 1950. The results indicate that the steep slopes, impermeable lithology and thick vegetation accelerate the flow of rainfall. In other words, flood events are also formed in an elongated basin. This result will help in better understanding relationships between the flood events and basin shape for basin area planning and management.