Morphometric analysis of the bottom topography of a large valley reservoir during its evolution

Abstract

Until now, the study of the morphology of the bottom of large reservoirs, subject to gradual siltation, received little attention. Morphometric descriptions of reservoirs are limited by the type, shape, altitude position, size of the bed, and the volume of water in them. The article presents the results of the analysis of the bottom relief of the Krasnodar Reservoir and the transformations of this relief for 2005–2021. The analysis was performed based on the materials of bathymetric surveys for the regulated volume of the reservoir on an area of 224 km2 with the construction of the corresponding digital relief models. The relief of the bottom of the reservoir is represented by flat areas of a flooded accumulative plain with prevailing slopes of about 0.2–0.4°, dissected by river channels of lower order tributaries. The transformation of the relief is caused by gradual siltation. The total volume of deposits for the specified area in 2005–2021 amounted to 127 million m3 with an average silt layer of 0.4 m. To describe the morphological properties of the bottom topography, we used geomorphometric techniques with the calculation of the BPI (Bathymetric Position Index) and the classification of mesoscale landforms based on it. For the bed, relief forms have been established related to three types of surfaces: flat (lower bank shelf), concave (depressions, deep depressions) and convex (reef crests, back reefs, mid-slope reefs). The constructed maps reflect the differentiated morphology of the bed surface, the evolution of landforms under conditions of continuous transformation of the basin, and also make it possible to judge the prevailing processes of morphogenesis. The coastal zone and the shallow part of the bed are the most complex in morphological terms. Here, along with reefs of different genesis, deep depressions and depressions in the form of underwater channels in advanced deltas can form on the accumulative shoal.