Response of the Dnieper river fluvial system to the river erosion caused by the operation of the Kaniv hydro-electric power plant (Ukraine)

Abstract

The commission of the Kaniv dam in 1973, as the last of the six dams on the lower Dnieper River cascade, changed the river regime completely. A description of these changes and their impact on the evolution of the fluvial anastomosing system form the aims of the study. The operation of the hydroelectric power plant (HPP) in Kaniv significantly affected the erosion and accumulation of sediment on valley floor and thus changed the fluvial system of the Dnieper River below the dam. The HPP initially operated on a hydropeaking system (until the early 1990s) and then on a run-of-river system. This study used the indicators of hydrologic alteration (IHA), the RB flashiness index, archival topographic and bathymetric maps, hydrological and sedimentological field studies, and satellite images to assess how the magnitude and duration of changes in the flow regime affected erosion and accumulation processes on the river bed and changed the pattern of channels as well as the landforms separating them.Until the commission of the dam in Kaniv, the fluvial system of the Dnieper River in its undisturbed state was a sand-bed channel but was then transformed from a braiding to an anastomosing river system. This was achieved by bars where consolidation of vegetation on fine clastic deposits created interchannel areas and islands. During the operation of the hydropeaking system, characterised by frequent artificial flows of short duration, channels became incised and narrowed. Interchannel areas were divided up into islands. Then, after the HPP switched to working a run-of-river system, the islands began to merge again into interchannel areas. This happened as a result of intensified erosion processes in both the main and the side channels. The operation of the HPP, by changing the flow regime and sedimentation processes in the river valley, modified the natural process of evolution of the fluvial system of the Dnieper River.