TERRITORIAL FEATURES OF THE INTRA-ANNUAL DISTRIBUTION OF RIVER FLOW ON THE VOTKINSK RESERVOIR CATCHMENT

Abstract

The article is devoted to the study of spatial regularities of the intra-annual distribution of flow on the rivers of the
Votkinsk Reservoir catchment in years differing in water content. An analysis of existing hydrological zoning schemes of the study
area showed that they differ significantly from each other, both in the number of the identified taxonomic units and in the location of
their boundaries. We revealed a discrepancy in the time of the onset of the water regime phases within the boundaries of taxa in the
hydrological zoning scheme given in [15, 1973] due to their strong generalization.

When using the scheme of A.S. Shklyaev [11, 1966], an analysis of the intra-annual distribution of flow is impossible due to the small
number (1-5) of centers of gravity of river catchment areas falling into the districts. Therefore, we clarified the boundaries of the hydrological
zoning of the study area. As the homogeneity criterion we used groups of hydrographs on rivers with the same dates of the beginning, maximum, and end of the spring flood and summer-autumn rain floods as well as the values of their monthly flow share in the annual flow.
A total of six regions have been identified: the northern mountainous region (the rivers Vishera, Berezovaya, Yazva, Yayva,
Kosva, and the Upper Kolva); southern mountainous region (the Upper and Middle Chusovaya River with the tributaries Usva, Vilva,
Vizhay, Koiva, Serebryannaya); northern lowland region (the rivers Chernaya, Veslyana, Lupya, the upper parts of the Kama, Lolog,
Kosa, Urolka, Pilva, Visherka, the Middle and Lower Kolva); central lowland region (upper parts of the Kama River, basins of the
Kondas, Inva, Obva rivers); south-eastern region (the basin of the Sylva River and the Lower Chusovaya River); southwestern region
(watersheds of the small rivers Ocher, Tulva, Gaiva, Mulyanka). Within the selected areas, there is noted a correspondence in the time
of the onset of the main phases of the water regime on the rivers.
We investigated the influence of ongoing climate changes on the intra-annual distribution of river flow in the Votkinskoe
Reservoir catchment area for two observation periods (1956–1977 and 1978–2021), before and after the onset of pronounced changes
in long-term fluctuations in annual runoff. For the period 1978–2021, on all rivers of the study area was revealed a decrease by 7.3%
in the share of spring flow on average by region, and an increase in summer-autumn flow for the central and southern regions of the
catchment area (from 13.6% to 26.4%) and winter flow (up to 22. 9%).