Physical experimental investigation of the horizontal water flow patterns in the Golden Horn under different scenarios with the presence of various structures

The Golden Horn estuary serves as a prominent symbol of Istanbul's history, its beauty, and its richness. Considered the world's largest natural harbor, the Golden Horn is an inlet of the Bosphorus, that geographically separates the historical center of Istanbul from the rest of the city. From its shining golden colored water at sunset to the horn-shaped sheltered harbor it creates, for thousands of years, the Golden Horn estuary has been a major economic attraction and has served as a critical military advantage for its inhabitants. The estuary connects the Bosphorus Strait with the Sea of Marmara and merges two rivers, the Kağıthane and Alibeyköy. Despite its significance, up until two decades ago, the Golden Horn estuary was a victim of industrialization, urban sprawl, and considered a prime dumping spot for industrial waste. Most research of the Golden Horn has focused on its pollution; in this paper, we explore the hydrodynamics of the Golden Horn. In this study, a physical experimental hydrodynamic model of the Golden Horn is developed to explore four different scenarios of possible bridge structures to enhance travel and commerce routes. These scenarios are: i) Keeping the natural condition of the estuary without structure (Scenario-1) ii) The presence of the Atatürk (Unkapanı) Bridge (Scenario-2), iii) the presence of a submerged bridge within the estuary (Scenarios-3) and iv) both the Atatürk (Unkapanı) Bridge and a submerged bridge existing in the estuary (Scenario-4). The structureless scenario is considered as a reference model to help evaluate the structural effects on the hydrodynamics of the Golden Horn. For each scenario, the physical experiments are conducted under flowrates 0.83, 1.11, and 1.39 L per second and flow patterns of the Golden Horn investigated. Eddies, shore flows, and regional flows are identified, and the effects of the structures revealed. The results of this present study show that the floating bridge has the highest impact on the horizontal water flow. Double bridge presence in the estuary has a mild effect, and the underwater bridge has relatively minor effects on the horizontal flow patterns of the Golden Horn.