Fluvial response to the Late Valdai/Holocene environmental change on the East European Plain

Abstract

The relicts of large meandering paleochannels are found throughout the territory of the periglacial zone of the last (Valdai=Weichselian) glaciation on the Russian Plain, on the lower levels of river terraces and on the floodplains. Channel widths of so-called macromeanders can be 15 times larger than the recent meanders on the same rivers. Paleolandscape and paleohydrological reconstructions show that such periglacial river channels were formed under the conditions of high spring water flow, up to eight times greater than modern discharges, when the flow coefficient was close to 0.9–1.0 due to the existence of permafrost. Also, summers were dry and streams lacked ground water supply. Permafrost degradation increased soil permeability in the spring and increased ground water flow during summer, causing a decrease of annual flow 12,000–14,000 years BP in the southern periglacial zone, and up to 8500 years BP in the northern periglacial zone. In the taiga zone, an annual flow in the recent river basins is about 80–85% of that found in the periglacial zone in the east, and 30–60% of that in the west. In the east of the broad-leaved forest zone, it is about 40–50% of that of the periglacial zone, and 20–25% in the western part of the broad-leaved forest zone. In the eastern steppe and forest steppe, the modern annual flow is about 40–60% of that of the periglacial zone and about 10% in the western part of steppe and forest steppe zones. As a result, large periglacial channels were abandoned and transformed into floodplain lakes and bogs. The Holocene channels have much smaller channel widths and meander lengths, formed under conditions of lower annual flows and much steadier flow regime.