A study of the re-shaping of the backwaters of low-pressure hydrosystems in the lower reaches of lowland rivers

The article presents the results of long-term field studies of the re-formation of water courses in the zone of the Takhiatash hydroelectric complex. It was noted that due to low water, for a significant part of the year, the Takhiatash dam worked with fully closed gates in all spans. In these years, the role of regulating the level regime of the shield dam is almost lost, and the end regulators of the main channels are regulated. The data of comparison of actual expenses, turbidity and back-up at the Takhiatash hydroelectric power plant with the calculated ones are presented. It is proved that sharp fluctuations in the water level in front of the dam and water intake into the channels lead to changes in the hydraulic and alluvial regime of the shield dam and channels. As the analysis of the survey of the riverbed cross-sections in the headwaters of the Takhiatash hydroelectric complex showed, in the initial period of operation, the bottom marks in the upper stream are increasing and the bottom marks in the lower stream are decreasing. Further years of operation (after 1982) were characterized by the stability of the flowing riverbed processes, that each characteristic year has its own level and consumption regime. It is noted that in high-water years there were no difficulties with water intakes, and the main difficulties are associated with the passage of flood flows through the shield dam. In recent years, there has been a rapid rise in the water level in the upper reaches, despite all the open dam gates, shipping locks and water intake structures, which are explained by the influence of the drifted streams on the capacity of the shield dam. It is proved that without any damage to the water intake during the growing season, it is possible to effectively flush the upstream with a constant decrease in the water intake coefficient - Kv < 0.55. Practically, this means for the Takhiatash hydroelectric unit that the flushing flow rate should not be lower than Q ≥ 250 – 300 m3/s.