FORMATION OF THE FLOODPLAIN OF THE KOLYMA RIVER IN THE SEIMCHANO-BUYUNDA DEPRESSION

Data are reported on the formation of the floodplain of the Kolyma Riv er in one of the depressions in the interior of the Magadan region. Th e average rate of the vertical growth of the floodplain reaches 3.3 cm /year; the value of side inwash is 6.1-16.3 m/year for the period 1941 -90. After the discharge of the Kolyma Hydroelectric Power Plant had b een regulated, the floodplain growth first increased and then decrease d: (1) before the plant construction (1941-79) - 3.6-11.3 m/year; (2) during the reformation of the hydrological regime (construction stage: 1980-85) - 13.2-38.6 m/year; (3) upon adaptation of the channel to th e new hydrological regime(introduction of the plant into operation, 19 86-90) - 3.9-9.0 m/year.