Comparison of adjacent basins in terms of morphological and hydrological characteristics

Defining the characteristics of a basin is extremely important in terms of creating maximum utilization rate from a basin. Recognizing the impact of the structure of a basin on the hydrological process and its morphological characteristics is essential parameters for conducting a research on a basin. Morphological analyses carried out on basins enable us to acquire quantitative data and thus to gain scientific insight about the hydrological structure of the basin studied. In this study, the Büyük Menderes River Basin and Gediz River Basin, which extend across a long valley and flow into the Aegean Sea, were selected as the research field. Soil and Water Assessment Tool (SWAT) software was used to examine important morphological characteristics of the two basins and the hydrological effects of morphological characteristics on the basins and similarity parameters between the adjacent basins were reviewed and compared. The Büyük Menderes Basin and Gediz River Basin are named after the Büyük Menderes River and Gediz River which have the biggest impact on the basin area. The basins bear significant water resources for the region and; in this context, water management of the basins is attached great importance. Depending on the landform, the morphological characteristics of the basins have an indispensable effect on the hydrological characteristics. To this end, the morphological characteristics of the Büyük Menderes Basin and Gediz Basin were identified and accordingly morphological parameters were calculated with a view to obtaining preliminary information on the hydrological characteristics of the basins. By using the model software; single hydrological units, which have the same hydrological reactions, have been defined by overlaying land use, soil and slope parameters. For the hydrological simulation in model software, meteorological data play an important role. Flow, water and sediment efficiency have been simulated by including meteorological data such as rainfall, temperature, humidity and solar radiation. In this study, for the stations located in the Buyuk Menderes River and Gediz River Basins, 26 years (1988 - 2014) of data were downloaded. While these data can be used in text format, required database table for the model is available by downloading Excel Macro file found in model home page. Morphometric parameters such as Linear (Stream Order, Bifurcation Ratio, Length of Overland Flow, Length of Main Channel, Channel Index, Valley Index, Hydraulic Sinuosity Index, Topographic Sinuosity Index, Standard Sinuosity Index); Areal (Basin Area, Basin Length, Basin Perimeter, Form Factor, Circularity Ratio, Elongation Ratio, Texture Ratio, Stream Frequency, Drainage Density); Relief (Relief Ratio, Ruggedness Number, River Gradient, Hypsometric Index) morphometric parameters were calculated and hydrological reactions of the basins were evaluated from these parameters.To calculate the drainage network, Digital Elevation Model data at 10 m spatial resolution was used as an input in the model interface, and the obtained drainage network was ordered according to the Strahler's stream ordering method. The important parameters such as bifurcation ratio, drainage density and stream frequency were calculated by using the extracted drainage networks. Bifurcation ratio plays an important role in forecasting the hydrological regimes of the drainage basins. It provides information about the shape of the basin and its flow characteristics. If this ratio ranges between 3 and 5, this means that the geology of the basin is homogeneous. The Buyuk Menderes and the Gediz River Basins have relatively similar bifurcation ratios and indicate the characteristics of the this group. The model's hydrological calculations were carried out based on the Hydrological Units. Final results were obtained by summing up all the calculations for all the basin. The accuracy and scale of necessary soil and land use data bear importance for Hydrological Units to be obtained. The accuracy of flow value calculated by the Model depends on the accurate calculation of these units. Model uses a dispersed file structure. Some of the calculations such as including the meteorological data in the model were made with different tools than the model itself. The Model uses FAO-UNESCO soil classification system. However, the classification system used for the land use is different than CORINE (Coordination of Information on the Environment) Land Cover. In this study, the two basins were examined and the effect of the morphological characteristics on the hydrological structure as well as the reactions in the two adjacent basins were analyzed. In these morphologic analyses, the following results were obtained; The Buyuk Menderes River Basin which has lower drainage density has a higher level of infiltration capacity compared to the Gediz River Basin. The time of concentration is shorter in the Gediz River Basin. The Gediz River Basin, which has a higher stream frequency parameter, has lower permeability than the Buyuk Menderes River Basin. Due to the fact that both basins are narrow and elongated, the time of concentration is longer in each basin. The Gediz River Basin, whose texture ratio parameter is high, is less permeable. Because the Gediz River Basin has a high value of ruggedness number, it has a higher probability of peak flow. The Buyuk Menderes River Basin is more sloping and therefore the velocity of the flow of water is higher. The obtained flow values were higher than the flow values calculated for the Büyük Menderes River Basin, whereas they were lower than those of the Gediz River Basin. The Model is run with the default value "1" for the factor affecting the soil conservation. When the calculations were made according to this, for both of the basins the sediment efficiency were calculated higher than the obtained calculations. When the calculations were made after the default value was reduced, the obtained results were closer to the calculated value of sediment efficiency. The calculated morphological parameters and model simulation results were compatible. However, there are differences between the calculated values and estimated values. As a result of the study, it has been determined that Büyük Menderes Basin whose drainage intensity is lower than Gediz Basin have a good penetration feature. Accordingly, it is considered that it concentration time will be longer than Gediz Basin. It was seen that morphometric parameter of stream frequency took a high value in Gediz Basin and this supports the idea that ground of Gediz is not permeable. Again, when these two basins were analyzed in terms of texture parameter, it is inferred that Gediz basin whose texture parameter is high is less permeable than another one. When topography for basins was analyzed, it was determined that topography value of Gediz is higher than another. Accordingly, possibility of peak flow is higher in Gediz Basin. Specified parameters and results of other morphometric parameters calculated were also verified by running the SWAT model. Especially, equal amount of rainfall was provided for both basins by manipulating the rainfall data and in this case, reactions of the basins verified the pre-information taken from morphometric parameters calculated. One of the results calculated by using model is that permeability of Gediz Basin is low and amount of water collected on the surface is higher than of Büyük Menderes. When it was evaluated with underground water reserves, this data was verified with the help of the information that annual reserves of underground water of Büyük Menderes Basin is double the amount of Gediz Basin. With the help of the study, effects of morphological structure on hydrological structure and different reactions coming from these two basins which are neighbor to each other by analyzing these two basins. Similar areas of hydrological reaction have been identified for the two adjacent basins examined within the scope of the study. It is also observed that conducting pre-evaluations on hydrological characteristics of the land by means of using the morphological parameters would promote the efficacy and efficiency of the related studies. In addition, it is assumed that using all the calculations and evaluations obtained from this study on the Büyük Menderes Basin and Gediz Basin for all other basins would benefit the development and improvement of new parameters.