This study aims to investigate the causes behind the constant flooding in the Biga River basin. It aims to determine if the river sub-basins's morphometric features was the reason behind the floods. Historical data from previous floodings were used to create the linear (one-dimensional), areal (two-dimensional), and relief (three-dimensional) morphometric properties of the sub-basins. These parameters were then evaluated quantitatively and a Digital Elevation Model (DEM) with 10 m resolution produced from 1:25000 scale topography maps as the base data. The D8 flow and Strahler methods were alos used as part of this study.The values obtained from the sub-basins of the Biga River were then weight and the potential to generate floods on the main stream of the sub-basins were evaluated. Our final conclusion indicates that the Biga sub-basin has indeed a major effect on flooding of the main channel of the Biga River. Changes in the frequency and severity of precipitation, due to climate change has led to the increase the occurrence of flood disasters worldwide. Because of this flood investigation is becoming more important as it can help determine how flooding occurs and how to prevent or minimize its impact. There are many different methodology are now being used to determine how flooding occurs, one of which is the basin morphometry parameter. This is one of the more practical methods and effective methods used to predict floods. For this study we use this methodology to study the Biga River Basin. This is one of the southern Marmara Sea basins on the Biga peninsula, and it includes can and Biga provinces within the borders of canakkale province. The basin covers about 2311 km(2) and there are four sub-basins included in the main branch. People of the region have been affected socially and economically by massive flooding of the Biga River, which is now a yearly occurence. Using basin morphometry parameters, we focus on the river's sub-basins. We used the one-dimensional linear morphometry (1D: Bifurcation ratio, R-b; stream length ratio, R-l ; texture ratio, T; drainage texture ratio, R-t), two-dimensional areal morphometry (2D: Drainage density, D-d; stream frequency, F-s; form factor, R-f; gravelius index, K-g ; elongation ratio, R-e), and three-dimensional relief morphometry (3D: Basin relief, B-h; times of concentration, T-e; relief ratio, R-h; hypsometric curve, H-e; and hypsometric integral, H-i). Using these parameters, the Biga River sub-basins were examined to determine their effects when they overflow into the main channel. The basic subdivision used in calculation and mapping of the morphometric parameters through Geographic Information Systems. The DEM is used to determine four different basins comprising the main cove in the Biga River basin. Several steps have been taken to determine the Biga River basin and sub-basin boundaries on the DEM. They are filled DEM, flow direction, flow accumulation, extraction drainage network, pour point, and watershed creation stages. In the extraction of the drainage process from flow accumulation, a threshold is given for the smallest stream unit. The Strahler method was used to classify stream indexes. ArcGIS 10.x software and the Spatial Analysis extension tool were used to calculate the morphometric parameters, i.e., drainage network properties, basin geometry, and basin relief properties and to determine basin boundaries. The general slope characteristics of the basin vary between 0 and 54.1 degrees. The distribution of basin relief features at different rates in the lower basins has different drainage densities and stream ratios as well as different erosion activities. The highest values of relief are in the Kocadere sub-basin, and the lowest values are in the Kocabas sub-basin. In the regional distribution of the lower basins, the Biga sub-basin has the highest spatial distribution and is observed in the lower basin of the Kocaba River. Basin drainage has a dendritic river apex. The rate of bifurcation varies. Fishing rate value ranges from 3.92 to 4.49, indicating that the watershed has a homogeneous structure. The drainage density of the basin is between 2.64 and 3.01, and the river density vary between 6.16 and 7.1. These ratios indicate that the infiltration surface runoff is high and that the infiltration values are low. The relief ratio shows that the surface runoff of the basin is very high, and the groundwater potential is moderate. The drainage texture of the sub-basin with the lowest value-the Kocabas sub-basin-is 6.16, and the highest value- Kocadere sub-basin-is 7.1, which indicates coarse and very coarse textures. Kocadere, Kirazhdere, and Biga sub-basins validate that these subwatershed are located under non-dense vegetation cover. Form factor results show that some of the basin has high and short duration peak during flood events depends on geometric character of basin. All the morphometric parameters analysis results show a good relationship of the basin geometry. According to the morphometric results of all sub-basins, the shape, linear, and relief characteristics identified in the Biga subbasin are more susceptible to flood events than the Kocaba, Kirazlidere, and Kocadere sub-basins. Applying geomorphic indices to understand the flood process of sub-basins into the main channel is very useful for planning and creating mitigation strategies before flood events. To understand the flooding process, characteristics such as geomorphology, climate, and land use must be considered.
