Temporary Dynamics of Water Temperature in the Carpathian Dam Reservoir (Besko in the Upper Vistula Basin)

Abstract

The study analyzes the temporal dynamics of water temperature in the vertical profile of the Besko reservoir located on the Wisłok river (upper Vistula river basin) in the Polish Carpathians. The data from 5-year water temperature monitoring were used in the analysis. Field surveys were conducted near dam of the reservoir (once a month) in the years 2014-2018. Measurements were carried out in the interval, every 1 m from the surface of water towards the bottom of the reservoir with using an electronic thermometer. The results of the studies showed that the Besko reservoir presents a typical for Carpathian dam reservoirs dynamics of thermal conditions during the year, strictly dependent on changes in thermal conditions of the air. Strong relations between water temperature and air temperature are gradually weakening along with the depth of the reservoir. During the summer, thermal stratification develops in the reservoir with vertical, several-degree temperature drop with a depth. The thermocline forms at smaller depths than in other large Carpathian reservoirs. In winter, reverse stratification is created in relation to the summer period, characterized by an increase of temperature values from the surface (covered with an ice) towards the bottom of the reservoir, and the difference in temperature values is 2-2.5°C. In autumn and spring, transitional thermal conditions between summer and winter periods develop which exhibiting homothermia features. In addition, the state of homothermia in the reservoir is also observed in the case of so-called warm winters.