Modeling of hydraulically controlled exchange flow in the Bosphorus Strait

Abstract

Recent hydrographic observations obtained in the Bosphorus Strait illustrate several features of the flow that may be related with the internal hydraulics. A two-layer numerical model indicates that the two-way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills, a contraction and abrupt expansion of the width of the strait. The model identifies three distinct regions of the supercritical flow. The lower-layer flow of the Marmara Sea origin is directed to the north towards the Black Sea in a progressively thinning layer and is controlled by the sill located near the Black Sea entrance of the strait. The upper-layer water of the Black Sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10-12 km away from the Marmara end of the strait. The upper-layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic jump and becomes subject to another critical transition near the abruptly widening exit section into the Marmara Sea. The controls exerted by the northern sil and the contraction are connected by a subcritical region whereas the supercritical conditions downstream of these controls isolate the two way exchange from the conditions in the adjacent regions. In this way, the requirement for the maximal exchange is met implying that the Bosphorus Strait achieves the maximum possible transports in the layers depending on the magnitude of net barotropic transport.