Experimental investigation of surface flow patterns in Golden Horn estuary, Istanbul

The Golden Horn has always been a prominent symbol of Istanbul up to present time. Several districts of Istanbul, Kağıthane at Northeast, Eyüp at Northwest, Fatih at Southwest and Beyoğlu at Southeast surround the Golden Horn which is approximately 7 kilometers long. The narrowest and the widest parts of the Golden Horn are approximately 150 and 750 meters, respectively. Kağıthane and Alibeyköy creeks flow into the estuary. These creeks carry the urban load into the Golden Horn. Until two decades ago, the region struggled with pollution problems that decreased the biodiversity and caused malodour. Because of the high pollution problem, researches have focused on pollution problem without taking the hydrodynamics of the Golden Horn into consideration. In this study, experimental hydrodynamic model of the Golden Horn under three different scenarios is developed. The flow coming from Bosphorus strait constitutes the Golden Horn as an estuary. 7 km distance from beginning to end is a high distance for Bosphorus strait water to actually get in. For this reason, to increase the water quality of Golden Horn "Can Suyu" project has been established. The bathymetry of the Golden Horn varies between 0 and 40 meters. The shallow parts are near to the shores and deepest parts are in the middle of the Golden Horn. The depth is increasing through the end of the estuary. Also, there is a shallow bathymetry at the recess of the Golden Horn Shipyard. In this study, experimental invastigations have focused on surface flow patterns in Golden Horn under four scenarious, which are without structure (Scenario-1), Atatürk (Unkapanı) Bridge (Scenario-2), a submerged bridge (Scenario-3) and Atatürk (Unkapanı) Bridge and a submerged bridge considered together (Scenario- 4). The experimental model scale is 1:80. The velocity of surface water was measured under three different experimental models. The velocity measurement data was used for development of vector maps. To constitute an accurate vector field, a physical mesh was designed based on 50 points where grid cells were selected as 1m x 1m. The points were marked with a spray dye which provided measuring the velocities at exact same location. Laboratory type acoustic doppler velocimeters were used to measure surface velocities. Sontek and Nortek brands were utilized for the experiments which are highly accurate. To calibrate the measurements between the two instruments, they were adjusted to same settings. To avoid sound mixing between two devices, they were departed at least 5 meters away during the measurement of the velocities. To guarantee that the measurements were taken at the same depth a limnograph (millimeter) was used. In addition to these instruments, an ultrasonic flowmeter was also used. The discharges were evaluated at three different values which are 3 m3/ h, 4 m3/ h and 5 m3/ h. The flow velocity data were measured and provided by using SONTEK and NORTEK instruments and their softwares. Despiking method was applied for eliminating the noise from the measurement data. The software Surfer was used for development of the velocity vector maps. The experimental models were developed to determine the surface water flow patterns in Golden Horn under four scenarious which are, natural situation of the estuary without structure as termed Scenarios-1, Atatürk (Unkapanı) Bridge as termed Scenarios-2, a submerged bridge model applied as termed Scenarios-3 and Atatürk (Unkapanı) Bridge and a submerged bridge modeled together named as Scenario-4. The structureless scenario is considered as reference model to evaluate the structure effects on the hydrodynamics of the Golden Horn. For each scenario, flowrates 3, 4 and 5 cubic meters per hour were implemented. Based on the results of this study eddies, shore flows, regional flows, and also effects of structures and bathymetry are observed.