PATTERNS OF SUSPENDED SEDIMENT LOAD SEASONALITY ALONG THE LENA RIVER BRAIDED CHANNEL
S.R. Chalov, M.K. Tarasov, A.S. Chalova
Lomonosov Moscow State University, Moscow, Russia
Keywords: suspended sediment concentration, sediment budget, remote sensing methods, braided channel, runoff distribution in branches
Abstract
Based on water sediment concentration modeling using the collection of Landsat images for the period 1992-2018, highly detailed (30-m resolution) features of suspended sediment load along the 200-km braided channel reach of the Lena river from Pokrovsk to the mouth of the Aldan river (upstream of the Aldan braiding) are described. It is shown that large anabranching river reaches correspond to changes of the system of sediment transport and accumulation manifesting themselves as a predominance of occurrences of positive (increase) or negative (decrease) DS0 values (where DS0 stands for suspended sediment concentration budget). The conditions of longitudinal decrease in suspended sediment concentration along the length of the braided reach of the Lena river are characterized by high water discharges (>20 000 m3/s) and are associated with sediment accumulation at riffles and floodplain areas. It is established that a significant role in the longitudinal decrease in water sediment concentration is played by lateral floodplain branches which accumulate a part of the incoming suspended sediments and have a dilution influence on the sediment flow downstream of the confluence with the main channel. Cases of a longitudinal increase in water suspended sediment concentration are typical for the lower water flow rates (<20 000 m3/s) and are connected increased bank erosion due to thermal erosion in summer as well as erosion of riffles during a low-water period. A combination of the grid of suspended sediment concentration, velocities and channel depths with a 30 30-m resolution (more than 20 000 cells) for low-water conditions revealed a dependence of local suspended sediment concentration on the transporting capacity of the flow which was determined for separate verticals. A correspondence between the regime of certain reaches in different phases of water regime is observed. Such a correspondence indicates the mutual influence of the directedness of mass exchange and channel morphology. The transformation of distribution systems of suspended sediments can be interpreted as one of the self-regulation mechanisms in the channel system. Complex systems of sediment flow distribution along the channel of a large river reflect the opposite directedness of erosion-accumulation processes caused by bends in the longitudinal profile.
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