ANALYSIS OF THE INTRA-ANNUAL RUNOFF DISTRIBUTION OF THE DNIESTER LEFT-BANK TRIBUTARIES WITHIN THE TERNOPIL REGION

Abstract

The Dniester basin is characterized by heterogeneity and diversity of water runoff formation conditions. Therefore, the issue of studying the basin of this river and its tributary basins has always received attention from scientists. Despite a fairly large number of publications, especially those analyzing the hydrological regime of the rivers of Ternopil, there are still no comprehensive studies of river-basin systems in the region. The Dniester River basin within Ternopil Oblast includes 1174 rivers and streams with a total length of 5195 km. The main feature of the Dniester basin’s hydrographic network is the absence of significant tributaries: there are only 6 medium rivers in Ukraine (two of which are within Ternopil Oblast – the Seret and the Zbruch rivers). Small rivers with a length of up to 10 km prevail, and their total length is 94% of the total length of all rivers in the Ukrainian part of the basin. This research focuses on small and medium rivers such as the Zolota Lypa, the Koropets, the Strypa, the Seret, the Nichlava, and the Zbruch. To assess the trends of long-term fluctuations in runoff characteristics and distribution of runoff within months and seasons, we used data from observations of the average annual water flow at 11 hydrological stations on the left bank of the Dniester. The period used for the research is from the beginning of the observation to 2020 inclusive. Using the difference integral curves, the long-term fluctuations of the average annual runoff of the left-bank tributaries of the Dniester for the selected observation period were estimated. It was found that the fluctuations in the runoff characteristics of the studied rivers are generally in-phase, and for some hydrological stations – synchronous. It has been established that the modern period is characterized by a downward trend in the values of runoff characteristics, which is associated with the impact of modern climate change and economic activity in river basins. Based on the analysis of the difference integral curves constructed for the studied rivers of the basin, a common water cycle was identified, which began in the mid-1960s and ended in the second half of the 1990s. Summarizing the above results of the study, we can conclude that, with the exception of some tributaries, fluctuations in the average annual runoff of the rivers on the left bank of the Dniester are natural. The current intra-annual distribution of runoff in the left-bank tributaries of the Dniester basin is characterized by a decrease in the volume of spring flood runoff, which is associated with an increase in air temperature during the period of snow accumulation and a decrease in precipitation in winter and an increase in the flow of the summer-autumn and winter low water marks as a percentage of the annual runoff between the studied periods..