Small river plumes off the north-eastern coast of the Black Sea
under average climatic and flooding discharge conditions
Abstract. This study is focused on the impact of discharge of small rivers on delivery and fate of fluvial water and suspended matter at the north-eastern part of the Black Sea under different local precipitation conditions. Several dozens of mountainous rivers inflow into the sea at the study region and most of them, except the several largest, have small annual runoff and limitedly affect adjacent coastal waters under average climatic conditions. However, discharges of these small rivers are characterized by quick response to precipitation events and can dramatically increase during and shortly after heavy rains which are frequent in the considered area. Delivery and fate of fluvial water and terrigenous sediments at the study region under average climatic and rain-induced flooding conditions were explored and compared using in situ data, satellite imagery and numerical modelling. It was shown that the point-source spread of continental discharge dominated by several large rivers during average climatic conditions can change to the line-source discharge from numerous small rivers situated along the coast in response to heavy rains. Intense line-source runoff of water and suspended sediments forms a geostrophic alongshore current of turbid and freshened water, which induces intense transport of suspended and dissolved constituents discharged with river waters in a north-western direction. This process significantly influences water quality and causes active sediment load at large segments of narrow shelf at the north-eastern part of the Black Sea as compared to average climatic discharge conditions.