Interannual and intra-annual changes in the Volga River water discharge in the alignment of the Zhigulevsk hydroelectric complex

Abstract

Interannual and intra-annual changes in river water flow play a decisive role in the formation of water quality and the functioning of aquatic ecosystems. For a quantitative assessment of long-term and seasonal changes in the water flow of the Volga River, an analysis of water discharge in the outlet section of the Kuibyshev reservoir (Zhigulevsky hydroelectric complex) for the period 1958-2019 was carried out. Almost the entire water flow of the Volga River passes through the bottom spillways of the hydroelectric power station and the overflow dam of the Zhigulevsky hydroelectric complex. The results of time series analysis showed that the average annual water discharge was 7,7 × 103 m3/s, the highest water discharge was 10,4 × 103 m3/s, and the lowest water discharge was 5,3 × 103 m3/s. Over a long-term observation period (61 years), it was established that the water content of the river is characterized by a change in low water and high-water periods. Statistical analysis revealed a positive trend for an increase in the average annual water discharge of the Volga River by 700 m3/s. Extremely low-water (1996, 1977, 1976, 1975, 1973, 1967) and extremely high-water (1994, 1991, 1990, 1981, 1979, 1966) years have been identified. The regulation of water flow at the Zhigulevsky hydroelectric complex has formed the seasonal variability of water discharge, which is characteristic of technical water bodies. Within the year, three periods are distinguished: winter low-water period (December-March), spring high water (April-June), and summer-autumn low-water period (July-November). The highest water discharges were observed during the spring flood (8,7-19,6 × 103 m3/s). During the winter and summer-autumn low-water period, the water discharge was 5,5-6,5 × 103 m3/s. The amplitude of fluctuations in the average monthly water discharge for the entire observation period was 2,1-33,5 × 103 m3/s.