Özet:

In this study, the morphometric characteristics of the river basins causing flood and overflow in Bulancak, west of Giresun, were evaluated. Bulancak is a settlement under the flood and overflow risk caused by the Pazarsuyu, İncüvez, Kara and Bulancak streams, which takes its source from the Giresun Mountains in the south. Pazarsuyu stream basin is much wider than other rivers and the flood and overflow risk is higher. Although the other basins have small basins, they are at risk for these streams due to the interventions made on the stream beds. According to the data from the Disaster and Emergency Management Authority (AFAD), nineteen floods occurred in these river basins between 1948 and 2012. According to geomorphological observations, with rapid population increase, the settlement was seen to expand from the coast to the inner parts and to occupy the river valleys. The use of stream beds in river valleys has caused narrowing of stream sections. When the morphometric features of the basins are combined with this situation seen in the lower basin, it has been determined that the frequency of the floods and overflows that turn into a disorder increases. Area and relief morphometry analyses of the basins were analyzed in order to determine the effect of geomorphological features on flood and overflow formation in Bulancak. Drainage density, stream frequency, basin form, length ratio and Gravelius index analyses were made to determine the spatial morphometric properties of the four river basins. In order to determine Relief morphometry properties, basin relief, relief ratio, ruggedness value, Time of Concentration, hipsometric curve and integral analyses were applied. In the analyses made using Geographic Information Systems (GIS), Digital Elevation Model (DEM) and geology maps covering the study area were used as basic data. According to the results of the analysis, the drainage density, stream frequency and ruggedness of all basins are high and basin shapes are narrow and long. Hipsometric curves and integral values indicate that the basins are at the stage of maturity close to bloom. Incüvez Dere and Bulancak Stream basins are seen to have higher flood and overflow potential according to the other basins.