The influence of hydro-meteorological factors on the bosphorus flow

Abstract

Straits are essential elements of coastal ecosystems, which not only host diverse kinds of species, but also serve the urban landscape offering recreational hotspots for the inhabitants. The hydraulics of straits are delicate and often complex, controlled by many meteorological and oceanographical factors such as tides, winds, waves, river runoffs and precipitation. Understanding the influence of each factor on the hydrodynamics of straits are vital for managing and protecting them, and also successfully adapting to the climate change scenarios. In this study, the flow dynamics in a strait, the Bosphorus, is studied under the influence of various hydro-meteorological flow drivers. Hydrodynamics of the Bosphorus is mainly characterized by the water level difference and density difference between the Black Sea and the Marmara Sea. Although the hydrodynamics of the Bosphorus has been studied by different researchers in the literature, the specific influence of each individual hydro-meteorological factors, especially wind blowing over the fetch of the Bosphorus, has not been investigated parametrically in detail. With this motivation, the present study focuses on the influence of hydro-meteorological flow drivers on the Bosphorus separately. The flow drivers, in general, are: (1) the water level difference between the North and South ends of Bosphorus (2) the density (specific gravity) difference between the North and South ends of Bosphorus (3) river runoffs into the Black Sea, (4) precipitation at Black Sea basin (5) the wind (velocity and direction) that blows over the fetch of the Bosphorus, (6) the wind that blows over the fetch of the Black Sea, (7) the wind that blows over the fetch of the Marmara Sea, (8) the atmospheric pressure differential over the Bosphorus, (9) tidal variations in the Marmara and Black Sea. In the first part of the study, the hydro-meteorological data time series, and the relationship/correlation between different variables are studied. The correlation and physical dependence between these variables are determined. In the second part of the study, a numerical model of the Bosphorus set in TELEMAC 3D is utilized to parametrically study the influence of the major ones of these hydro-meteorological drivers. Results on the timeseries analysis showed that there is a meaningful correlation between the water level difference (between the North and South ends of Bosphorus) and the wind characteristics, as expected. The parametric study indicated that most influential variable on the upper- and lower-layer hydrodynamics of the Bosphorus is the water level difference between the North and South ends of Bosphorus, which inherently includes all of the above-mentioned factors, except the density difference and the wind that blows over the fetch of the Bosphorus. The influence of wind that blows over the fetch of the Bosphorus is limited, and wind-generated water level difference in general is mostly inherited from the correlation between the wind and the water level difference (between the North and South ends of Bosphorus) variables.