SOURCES OF THE BASIN COMPONENT OF THE SEDIMENT YIELD ON THE SMALL RIVER IN THE FOOTHILL-LOWLAND ZONE OF THE BLACK SEA COAST OF THE CAUCASUS (USING THE EXAMPLE OF THE TSANYK RIVER)

Abstract

Listen

Translate article

Тhis study aims to evaluate features of the formation and sources of the basin component of the sediment yield during flash floods. Measuring campaigns were conducted in the weakly disturbed section of the Tsanyk River basin, located in the Greater Sochi area in the foothill-lowland zone of the Caucasus Black Sea coast. We used a set of field and calculation methods, including sediment dating with application of 137Cs, pin method, Yang's method, erosion modeling and others techniques for determining the rate of denudation and deposition processes. We investigated the processes of local and long-distance sediment movement. It was established that the rate of creep is 2-2.2 cm/year, the intensity of scree processes varies depending on the rock types in the range 1-3.5 cm/year. The processes of sheet erosion and linear erosion contribute to the movement of part of the eroded material from the catchment area to the river channel. Four types of slopes and slope catchments are distinguished according to the features of a sediment delivery from the catchment area to the river channel. The average annual sedimentation rate in the gully fan is amounted to 2.3 cm/year since 1986. At the same time, on the basis of studying the accumulative deposits of the gully fan, including the content of the 137Cs isotope in the different layers, it was established that the main sources of sediments are material produced by gully erosion, scree processes and slopes settling. 5-6 episodes of catastrophic sediment removal occurred in this particular slope catchment for 30-year period. The ratio between a sediment removal from the slope catchments to the river channel and the measured sediment yield in the Tsanyk River during the rain floods of low repeatability makes it possible to state that the basin component of sediment yield is at least 75% of the total. Information about the ratio of slopes and slope catchments of various types within the small river basins of the subtropical belt of the Black Sea coast of the Caucasus should be taken into account when calculating engineering structures for protecting infrastructure facilities from the impact of flash floods or mudflows.