Flow through the Golden Horn Estuary

Abstract

This paper presents the results of a numerical study on the flow through the Golden Horn, a natural estuary that connects with the Bosphorus Strait at the point where the Bosphorus meets the Sea of Marmara. The numerical model is a three-dimensional model, incorporated with the large eddy simulation model for the horizontal turbulence closure, and a modified mixing-length model for the vertical turbulence closure. It was found that, when viewed from above, there exists a clockwise vortex that forms at the entrance of the Golden Horn, driven by the north-to-south flow in the upper layer of the Bosphorus, penetrating O(1) km inside the Golden Horn. This vortex, with a north–south extent of O(5) km, extends to the north as far as Dolmabahce. The three-dimensional (3D) calculations also reveal the presence of a smaller vortex [with an extent of O(0.5) km] forming to the west of the former vortex, rotating in the counterclockwise direction. The aforementioned vortex system, comprising the clockwise and the counterclockwise vortices, penetrates O(2) km inside the Golden Horn from the entrance of the Golden Horn. The velocities at the periphery of the major vortex can be as high as O(0.5) m/s and those of the secondary one, O(0.1) m/s. This vortex system is maintained down to a depth of z = −15 to − 20 m. When moved toward the bottom, the aforementioned flow pattern changes at this depth to a pattern consisting of a counterclockwise major vortex and an accompanying clockwise minor vortex, driven by the south-to-north flow in the lower layer of the Bosphorus. The plan view extents of these latter vortices are O(1) and O(0.5) km, respectively. The depth where the flow pattern changes coincides precisely with the depth where the two-layer flow in the Bosphorus (at the entrance of the Golden Horn) changes direction, an important result, linking the mechanism of the flow in the Golden Horn directly to the flow in the Bosphorus. It was inferred that the previously mentioned vortices play a key role for the water exchange between the Bosphorus and the Golden Horn Estuary. The present 3D calculations showed that the effect of the upstream creeks (Kagithane and Alibeykoy) is felt only at the surface waters but not below, in the top O(1) m depth, a layer even shallower than the half depth of the water in the shallow-depth zone (within 4 km from the entrance) of the Golden Horn.