FIELD MONITORING OF ALLUVIAL SEDIMENT ACCUMULATION IN THE OKA RIVER FLOODPLAIN (IN THE MIDDLE PART OF THE ITS BASIN)

We present the results of using the method of sedimentation traps (mats) in geomorphological monitoring of alluvial sedimentation rates in the floodplain of the Oka River. Only two spring floods between 2014 and 2021 inundated the central (high) floodplain, resulting in the accumulation of a 0.45 mm layer of sediments. We observed sedimentation on the low floodplain annually. The average thickness of the mineral (according to National Standard 25100-2020) sediment layer on the mats reaches 19.8 mm/year. Only silty-clay sediments are transported far from the Oka River channel, and accumulation of sandy particles was noted in the river channel zone. We determined that the high floodplain at the monitoring points is inundated typically within 15 days, which corresponds to an average flood according to the V.I. Shrag's gradation. In riverine areas, the direct interaction between stream water masses and bank soils can extend for 1–6 months and is highly dependent on the type of spring and flood parameters. This allows us to identify such sedimentation settings as areas with regular manifestation of fluvial morpholithogenesis, sensitive to fluctuations in the climate of the Oka basin.