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SPATIAL-TEMPORAL DISTRIBUTION, GENESIS AND TRANSPORTATION OF BOTTOM SEDIMENTS

Lia Matchavariani, Giorgi Metreveli, Davit Svanadze, Zaal Gulashvili

Abstract

Genesis, transport and accumulation of settled sediments of mountain rivers are such random processes in time and space, which are defined by the river flow rate (Q m3/s?c), height of the basin (IпїЅ), the inclination of the river and basin geology. Genesis and the volume of river sediment is the function of the climate and, in accordance with its cycles, it increases during the warming period and decreases as the temperature falls. The main natural factors for sediment formation are the glacier, erosion, landslides and flax. Sediment transportation пїЅ the process of sediment transportation by the flow represents many variable functions, which are mainly described by Chezy-Maning and Airy laws. Aside from the aforementioned laws, this process is also subject to the regularity of dependence between the maximal diameter of the sediment (dmax) and the speed of the river (V, m/sec) in the head race of a water reservoir. In some places, the river crosses an uplifted ridge or пїЅepirogenic thresholdпїЅ and the submersible lowland. The river saws such threshold to create the so-called "equilibrium balanced riverbed" of respective characteristics. In case if the speed of the threshold uplift is more than the speed of the riverbed cut, then the depression is created, in which the river permanently deposits sediments in order to create riverbed with a corresponding inclination, so called equilibrium riverbed. Some rivers use the significant part of sediments for the compensation of stagnations caused by "flax dam" - alluvian fan of the flax. The result of such processes is the creation of Chiori grove, accumulative plain-terraces of Saglolo and Chrebalo in the basin of river Rioni, and the creation of Tianeti plain in upstream of river Iori and many more. The significant part of sediments is spent on the formation of sanding prisms of water reservoirs. River consumes one part of the remaining settled sediments to create balanced riverbed in the submersible lowlands and to neutralize the effect of sea eustasy. The second part of sediments is spent on the formation of delta, permanent filling of coastal beaches and creation of accumulative formations in the sea. The mountain reservoir is in conflicting relations with the sea coast protection, and the security of population and infrastructure at the head race. Hence, the genesis of settled sediments of the river, places of natural accumulation and sediment granulometry should be taken into account when choosing the place for reservoir. The optimal places for the construction of water reservoir dams are epeirogenic thresholds, since the dam is uplifted there and thus, the operation period of water reservoir is relatively longer.

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DOI resolver: doi.org/10.5593/sgem2017/31/s12.077

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