Influence of non-stationary river discharge on the quality of water withdrawal in the presence of density stratification

The paper presents the results of field measurements and numerical modeling of different aspects of water quality in the Kama River (Kama reservoir), which is the source of technical water supply of industrial enterprises of the city of Berezniki. During the summer season, there are significant risks related to sustainability of water supply. It is traditionally believed that, over the winter period of low water, these risks increase manyfold. However, the results of departmental monitoring and field studies performed in winter provide evidence of the performance stability of technical water intakes from the Kama river. It was found that, in summer, when this part of the Kama river is located in the backwater zone of the Kama hydroelectric power station and, respectively, the flow velocity decreases, vertical stratification of water masses is formed, which significantly reduces the stability of water use from the near-bottom area. In winter, with a decrease in the water level in the Kama reservoir, the typical river conditions characterized by increased flow velocities occur. Under these conditions, the intense vertical mixing of water masses is implemented, which improves the consumer properties of water for sustainable water supply. The numerical simulations carried out within the framework of a three-dimensional model confirmed this conclusion. It is shown that if the amplitude of the flow velocity at a point changes with time according to a harmonic law, then the value of the salt concentration at this point also changes harmonically, but in antiphase with the velocity.