The effect of total sediment runoff on erosion and accumulation processes in the valley of the Djankuat stream, Greater Caucasus

The article presents the results of the study of the suspended and bed sediment runoff for the modern period. In addition the features of sediment deposition within a valley bottom section of the Djankuat stream catchment (F = 9,1 km², Q_mean = 1,5 m³/s) with predominance of accumulation are discussed. Field research methods included direct measurements of bed load using the Helly-Smith sampler, determination of the average diameter of bed load and floodplain sediments, channel deformations and accumulation rates on the floodplain within the broader section of the valley floor, including the radiocesium dating method. It has been established that the total sediment runoff of the Djankuat Stream is 10,1·10⁶ kg/year, 13% of which is the bed load. According to the bed load sediment budget observations in 2016 and 2023, as well as the radiocesium dating of floodplain sediments, the accumulation rate on the floodplain within the broader section of the valley floor is 4,8–5,6 ± 1,0 mm/year over the total period since its origination (120 years). During 2016–2023 the volume of annual channel erosion within the same section is 1260 tons/year. The nine-fold difference between the average diameter of the bed load sediments and the median diameter of the floodplain sediments within the broader section of the valley floor indicates that the main deposition events are related to extreme floods with less frequent water discharges.

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