2. Structure of small river plumes

The process of transformation of freshwater discharge as a result of its interaction with saline sea water can be considered and analyzed on different spatial and temporal scales. Initially, river discharge inflows to sea from a river mouth and forms a sub-mesoscale or mesoscale water mass commonly referred as a river plume, where salinity is significantly lower than of surrounding sea water. Buoyancy force plays an important role in spreading and mixing of this freshened water mass; therefore, dynamics of river plumes and ambient sea is different because of salinity differences. Thus, salinity is the main characteristic that is used to distinguish river plumes and sea water, i.e., define the mixing zone where river plume ends and sea water starts.

A river plume is generally formed by one or multiple distinct sources. Structure and dynamical characteristics within a river plume are strongly nonhomogenous. In particular, salinity and velocity field in vicinity of freshwater source/sources are significantly different as compared to outer parts of a plume [9, 16]. A river plume is spreading and mixing with adjacent sea water, which results in transformation of
