Channel morphodynamics of the mouth section of the Olha River over a ten-year period

This article discusses the analysis of channel morphodynamics of the mouth section of the Olha River during 20092018 within the Shelekhovsky district of Irkutsk region (52°21'64.2"N; 104°13'65.8"E). The channel morphodynamics of the most developed small rivers has practically not been studied at the moment in the East Siberian region. Analysis of field and cartographic material, literature sources, as well as remote sensing data and satellite images made it possible to identify seven areas with three types of channel processes (Fig. 1), among which the following areas turned out to be the most dynamic: artificially straightened section of the channel in Olha village area, drained oxbow complex in Energetik garden partnership area, periodically drained section of the channel in the area of lake-like extension with degrading channel and oxbow lakes. The following floodplain-channel types were identified: a wide-floodplain meandering type of channel with free meandering bends, a meandering with adapted bends, as well as an adapted relatively straight type of channel. The climatic, geological-geomorphological and anthropogenic factors have the greatest impact on the dynamics of channel processes; the latter has made significant changes in the structure and type of the floodplain of the Olha mouth section during the study period. Additional calculations of the main morphometric parameters made it possible to determine the degree of bends development and the ratio of length to deflection arrow (see table). Calculations showed that for 2009-2018 there was a decrease in the degree of river meandering, a general decrease in the channel tortuosity and frequency of floodplain flooding, especially in areas of free meandering with a high degree of anthropogenic transformation. The analysis of the graphs of average daily flow rate and water level, flow rate of suspended and bed load sediment, as well as turbidity of the Olha River (Figs. 2 and 3) showed that the main increase in water flow in the river falls on the periods of spring floods and flash floods (May and August ). The disturbance in phenomena sequence was revealed: the first maximum of water level falls on March, while the first maximum of water discharges in May. The maximum water turbidity is observed in May, which is associated with passage of spring flood; the minimum falls on June. These values are correlated with the schedule of suspended and bed loads, passing the same maximums and minimums. Human economic activity led to decrease in frequency of floodplain flooding within the floodplain of the Olha River, which affected the area and number of oxbow lakes (Fig. 4). The process of floodplain type changing is observed from segmented-ridged type to segmented flat type.

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