4 results listed
In this study, approaches of Clark’s unit hydrograph and Nash based geomorphological instantaneous unit hydrograph were compared by using flow data of Dariören Gauging Station in Arıt sub-basin of Bartın Creek located in Western Black Sea Basin and precipitation data of Ulus Meteorological Observation Station. For this purpose, digital elevation map of the Bartın Creek Basin with a resolution of 10x10 m was created by using ArcGIS with 1/25 000 scaled topographic maps and the basin was modeled taking Darıören as the basin outlet. By using the digital elevation model and the flow directions of the basin, flow accumulation layer was determined. Drainage network of the basin was created by taking the threshold value of the flow accumulation as 100 cells. Some morphometric parameters such as bifurcation ratio, length ratio and area ratio were calculated using created drainage network to estimate the Nash based geomorphological instantaneous unit hydrograph of the basin. The rainfall-runoff relationship of the basin was examined using the HEC-HMS hydrological model. The effective precipitation in the basin was estimated using the SCS curve number method which takes into account the soil type and land use of the basin. Clark unit hydrograph and user-specified hydrograph methods were selected for transformation from the effective precipitation to runoff. The Clark’s unit hydrograph parameters such as the time of concentration and the storage coefficient were calculated by considering some approaches used in the literature. The model results were interpreted by using some statistical indicators and the approach which gave the best results was determined. According to the results, the Nash based geomorphological instantaneous unit hydrograph method was found to give better results than the Clark’s unit hydrograph method. Furthermore, curve number, time of concentration and storage coefficient used in the loss model and the Clark method were calibrated using the observed rainfall-runoff data and taking the predicted ones as the initial values. As a result of calibration, it was observed that the Clark method did not significantly improve the direct runoff estimation.
International Science and Engineering Application Symposium on Hazards
ISESH
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In this study, Gökırmak Basin located in the Western Black Sea Region was divided into 12 sub-basins and the geometric characteristics, drainage network and stream orders determined according to the Strahler approach of these sub-basins were calculated. Thus, the twelve morphometric parameters for each sub-basin thought to trigger the flood potential of the sub-basin were calculated. Afterwards, each sub-basin was prioritized according to each morphometric parameter using a method from the literature and the total grade of each sub-basin was determined. Then, it was noted that the top five prioritized sub-basins were considered to have high flood potential, two of which were in the drainage area of the Kirazlıköprü Dam built on the main channel. It was recommended that sediment could be trapped before reaching to the dam and the main canal by constructing sediment storage dam. Furthermore, it can be said that the Kirazlıköprü Dam was located in an important place in terms of protecting the city center from floods by routing the floods from the sub-basins with medium and large drainage basin area and medium flood potential in the drainage area of Kirazlıköprü Dam. Moreover, it is thought that a small scaled flood detention basin to be constructed in the sub-basin that carries a large amount of flow due to its drainage characteristics to the Arıt Creek that is located close to the city center will help in mitigation of flood damages.
International Science and Engineering Application Symposium on Hazards
ISESH
Müsteyde Baduna Koçyiğit
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In this study, the depth and shape of the scour hole formed under the deck of a bridge model without a pier and with a skewness angle of 15° between the deck and the channel flow was examined by a series of experiments under weir type of flow and clear water conditions where the water level rises and flows over the bridge deck and thus the bridge deck acts as a weir. The laboratory work was conducted in the Hydraulic Laboratory of Gazi University, Faculty of Engineering, Civil Engineering Department and the experiments were performed at different approach flow depths, discharges and girder heights. According to the experimental results, as the approach flow depth increased, the discharge and the depth of the flow overflowing the bridge deck increased and the discharge passing under the bridge deck decreased. Thus, the mean flow velocity passing under the deck and the bed shear stress also decreased, resulting in reduced amount of scouring in the bed. It was also noted that as the girder height increased, the depth of scour hole also increased. Furthermore, it was seen that the skewness angle significantly affected the shape of the scour hole and this situation is of great importance especially for river bridges with piers.
International Science and Engineering Application Symposium on Hazards
ISESH
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In this study, the peak flow rate of Akçay Basin located in the Western Black Sea Basin, which has a small drainage area with no flow data was investigated by using different number of sub-basins. For this purpose, the digital elevation model of the basin with 10x10 m resolution, flow direction and flow accumulation of each cell were determined by means of ArcGIS using 1/25 000 scaled topographic maps. According to different drainage networks, the basin was sub-divided into 1, 3, 7 and 13 sub-basins and basin models were established. Hydrological processes of the sub-basins such as infiltration, transformation from effective precipitation to runoff, and stream routing for models with more than one sub-basin were simulated by the HEC-HMS semi-distributed hydrological model using the Soil Conservation Service, Clark’s unit hydrograph and lag time methods, respectively. Curve numbers of the sub-basins were determined using the soil type and land use maps, the infiltration models were formed and effective precipitation was calculated. According to the Clark’s unit hydrograph method that was used for transformation from effective rainfall to direct runoff, the time of concentration was calculated using the Soil Conservation Service method. The storage coefficient was calculated by taking into account some geometric features such as the time of concentration, drainage area of the sub-basin and the longest flow path distance, as suggested in the literature. The lag time in streams was determined according to the lag time approach proposed by Soil Conservation Service. Of using the hourly precipitation data measured at the Çatalzeytin Meteorological Observation Station in September 2008, the direct runoff hydrographs were estimated for different number of sub-basins. According to the analysis results obtained by taking the number of sub-basins as 1, 3, 7 and 13, the peak discharges were determined as 323.27 m3/s, 300.86 m3/s, 336.49 m3/s and 361.10 m3/s, respectively. According to the results, it was noted that the maximum peak discharge was estimated for the model with the highest number of sub-basins.
International Science and Engineering Application Symposium on Hazards
ISESH
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Müsteyde Baduna Koçyiğit