METHOD FOR IDENTIFICATION OF EXTREME ANNUAL AND MONTHLY VOLUME OF RIVERS FLOW USING THE EXAMPLE OF THE DANUBE AND DNIEPER RIVER
DOI:
https://doi.org/10.47143/1684-1557/2023.1-2.5Keywords:
Danube, Dnieper, flow, spring flood, flood, low water, reservoir, flow regulationAbstract
Normal, high-water and low-water years are concepts that are widely used to characterize marine areas influenced by river flow. Understanding the hydrobiological processes of the sea depends on information about the volume of river water. In connection with this, a method for dividing river flow volumes into three gradations: normal, extremely high and extremely low is proposed. The boundaries between gradations are determined by the statistical properties of the analyzed series itself. Therefore, the boundaries are absolutely objective, that is, they completely exclude the role of the subjective factor of the researcher. In addition, the method is extremely simple. This method also turned out to be useful for identifying high-water (spring flood) and low-water (low-water) phases of the annual cycle of monthly flow volumes of the Danube and Dnieper. The fairly long and fairly modern observation series for 1981–2020 were used. This allows us to consider the months selected by our method as climatically determined high-water and low-water phases. The months of the high-water phase turned out to be the same for the Danube and Dnieper, but the months of the lowwater phase, and even their number, were different. Comparison of monthly river flows in a particular year with the climatic standard makes obvious cases of early onset or delayed completion of the phases of the annual cycle. Wet months beyond the spring flood are associated with large amount of intense precipitation. Using a numerical experiment and using the proposed method, a possible reason for the absence of low water on the Dnieper in some years is shown. In other words, the absence of low water is the absence of such low monthly flow volumes that would be below the upper limit of low water. This and some other differences in the annual cycle of monthly flows of the Danube and Dnieper are most likely associated with a very large difference in the degree of regulation of their expenses. As a measure of the regulation of river flow, we can take the ratio of the sum of the volumes of reservoirs that affect its flow to the annual average volume of river flow below the reservoirs. This measure, expressed as a percentage, is equal to 5 % for the Danube, and 110 % for the Dnieper.
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