Channel morphology and river flow in the northern Russian Plain in the Late Glacial and Holocene

The relicts of large meandering palaeochannels are found throughout the ter ritory of the periglacial zone of the Last (Valdai=Weichselian) Glaciation on the Russian Plain. Channel widths of macro-meanders can be 15 times larg er than the recent meanders of the same rivers. Palaeolandscape and palaeoh ydrological reconstructions show that these periglacial river channels were formed under conditions of high spring water flow, up to eight times great er than the modern discharges, when the flow coefficient was close to 0.9-1 .0 due to presence of permafrost, summers were dry and streams lacked groun d water supply. Permafrost degradation increased soil permeability in sprin g and increased ground water flow in summer, causing a decrease of annual f low (due mainly to the flood flow decrease in spring). As a result, large p eriglacial channels were abandoned and transformed into lakes and bogs. Lat e Holocene channels have much smaller channel widths and meander lengths. T hese were formed under conditions of lower annual flows and much steadier f low regime.