Piotr Gierszewski

Abstract The operation of dams is the key cause of river discontinuity, with reduced flow velocity towards dams reflected in gradual change in the physicochemical properties of water, the concentration and characteristics of suspension matter, and the properties of bottom sediments. In the case of dam reservoirs operating in a cascade system, the most major transformations of river-water abiotic and biotic characteristics take place in the first reservoir of the cascade, with properties of the aqueous environment in consecutive bodies of water then affected markedly. Detailed here, research conducted in the Upper Volga Reservoirs in Russia sought to assess the size and nature of changes in the physicochemical properties of water and in characteristics of the suspended material and bottom sediments that take place along the longitudinal profile of this Cascade of reservoirs. Results were then used to determine the relationships pertaining between the separate reservoirs of the Cascade, and to recognise the capacity for the typical longitudinal zonation to be reproduced in consecutive reservoirs along the cascade. The reservoirs of the upper part of the Volga Cascade are located in an area of limited environmental contrast. In such a situation, variability to the physicochemical properties of water and characteristics of the bottom sediments along the longitudinal profile are conditioned primarily by hydrological factors. The study showed that the functioning of the reservoirs as part of a cascade system did not result in the disappearance of the characteristic three-section aquatic environment, expressed by the presence of riverine, transitional and lacustrine zones. The equivalent of the riverine zones in the second and subsequent reservoirs are backflow zones, which extend to the dam of the upstream reservoir. The high-energy, erosive force of water downstream from dams denotes hydrodynamic conditions similar to those in the upper, riverine sections of reservoirs operating independently. The presented three-section model for the reservoirs was preserved mainly in terms of diversified bottom-sediment properties. A regularity detected entailed decreasing mean grain size towards the dam, and a parallel increase in OM content in the sediment. A significant impact on bottom–sediment properties is also exerted by the velocity and direction of currents, by depth and bottom morphology, and by the properties of the clastic material supplied to the reservoir from various sources. Only to a lesser extent is the three-section model of the aquatic environment in reservoirs evident in physicochemical properties of the water. However, the intense turbulence present in water below dams ensures such strong mixing that vertical gradients in water temperature are realigned, and oxygenation of bottom layers of water improved. In this sense, these particular sections of reservoirs are similar to the riverine zones of reservoirs operating independently. The presence of less-mineralised water in the lower, deepest sections of the reservoirs and below dams indicates a hydrochemical connection between the consecutive bodies of water. Furthermore, a significant influence on changes in the course of analysed parameters must be ascribed to local conditions, with the impacts of tributaries, but also other local factors like depth, the presence of erosional banks and intensity of shipping, proving just as important as causes of disturbance to the river continuum as dams.

Keywords: kaskada zbiorników zaporowych, nieciąłość rzeki, rumowisko rzeczne, górna Wołga, Rosja

Piotr Gierszewski [piotr.gierszewski@geopan.torun.pl], Institute of Geography and Spatial Organization Polish Academy of Sciences, Kopernika 19, 87-100 Toruń, Poland
Jarosław Kordowski [jaroslaw.kordowski@geopan.torun.pl], Institute of Geography and Spatial Organization Polish Academy of Sciences, Kopernika 19, 87-100 Toruń, Poland

Citation

APA: Gierszewski, P., Zakonnov, V., Kaszubski, M., & Kordowski, J. (2017). Transformacja właściwości wody i osadów w profilu podłużnym zbiorników zaporowych Kaskady Górnej Wołgi*. Przegląd Geograficzny, 89(3), 391-412. https://doi.org/10.7163/PrzG.2017.3.3
MLA: Gierszewski, Piotr, et al. "Transformacja właściwości wody i osadów w profilu podłużnym zbiorników zaporowych Kaskady Górnej Wołgi*". Przegląd Geograficzny, vol. 89, no. 3, 2017, pp. 391-412. https://doi.org/10.7163/PrzG.2017.3.3
Chicago: Gierszewski, Piotr, Zakonnov, Viktor V., Kaszubski, Michał, and Kordowski, Jarosław. "Transformacja właściwości wody i osadów w profilu podłużnym zbiorników zaporowych Kaskady Górnej Wołgi*". Przegląd Geograficzny 89, no. 3 (2017): 391-412. https://doi.org/10.7163/PrzG.2017.3.3
Harvard: Gierszewski, P., Zakonnov, V., Kaszubski, M., & Kordowski, J. 2017. "Transformacja właściwości wody i osadów w profilu podłużnym zbiorników zaporowych Kaskady Górnej Wołgi*". Przegląd Geograficzny, vol. 89, no. 3, pp. 391-412. https://doi.org/10.7163/PrzG.2017.3.3