ИСТИНА

Anadyr is the second largest river emptying into the Bering Sea, with an annual water discharge of 68.2 km3 and a catchment area of 191 000 km2. The minimal number of gauging stations in the basin with only water stage measurements available since the 1990s make it one of the poorly studied rivers in the Arctic region. Water discharge and turbidity measurements made in June 2021combined with remote sensing approaches shed some light on the flow regime and sediment budget of the middle reach of the Anadyr River (Markovo – Ust-Belaya section). The bulk of the discharge (60-70%) is supplied during flooding in June. Due to the minimal slopes and the relief of the territory surrounding the depression, the flooded area in high floods can exceed 3000 km2. At the same time, the share of the floodplain of alluvial genesis does not exceed 10%. The rest of the floodplain is inherited, representing the bottom of the former lake basin. The Anadyr river in the middle reach has an anabranching channel. The water flow distributes almost evenly (from 15 to 30%) among branches during spring floods. A distinctive feature of Anadyr is the interchange of rifts and deep (up to 35 m at low-water levels) stream pools. The small distance between rift crests and minor changes in the stream pools' morphometry over the last 50 years (according to sailing directions of the 1970s) suggests their pre-fluvial origin. The bank erosion rates within the section are highest in the semi-mountain branches, where the high sediment load leads to significant changes in the bed topography, and the average rate of change in channel position reaches 60% over 50 years. In the downstream part, the maximum rates are up to 2.6 m/year at the convex banks of the blocked bends. The total area of eroded banks in the studied section of the Anadyr is more than 14 km2 over the 2000-2019 period.