Hydraulic characteristics of the river flow and sediment transport conditions in the downstream pool of the hydroelectric complex

Abstract

In this paper, the navigable section of the Svir River, located in the lower reaches of the Nizhne-Svirsky hydroelectric complex, is considered. Special in-situ observations were made in this section to study the hydraulic regime of the river flow under the conditions of unsteady water movement. The study has showed that the kinematic characteristics of the flow in the downstream pool vary with the distance from the site of the waterworks and depend on the regime of the discharge flows. The nature of the transformation of releases in the downstream under open channel and ice conditions has been studied. The values and intensity of changes in the main characteristics of the river flow during the propagation of the tail water wave in the lower reaches such as the nature of changes in the level regime and the slopes of the free surface on the hydraulic structures, the regime of water flow velocities, have been evaluated. The main hydraulic parameters of the river flow such as the values of the Froude number, the Chézy’s coefficient and the water flow modulus are determined. The character of changes in local and convective accelerations is studied and their contribution to the general value of energy losses along the stream length is evaluated. Numerical experiments make it possible to identify the peculiarities of sediment movement in conditions of unsteady water flow and to develop recommendations for modelling channel transformations in such conditions. It is found that during daily and weekly regulation of the river discharge, sediment transport is activated at the moment when a wave of daily water discharge is passing from the upstream reservoir of the hydroelectric power plant. At the same time, the basic parameters of sediment transport such as the speed of dune movement and sediment discharge increase in comparison with the stationary movement of the water.