Macromeanders of the Vorona River as evidences of high river runoff in the Late Glacial

Abstract

In river valleys of the East European Plain, on floodplains and low river terraces, macromaenders (large palaeochannels) are found. These macromeanders are evidences of high fluvial activity epochs, when the values of river runoff were several times higher than modern ones. Such palaeochannels were found and studied in Vorona river valley near Borisoglebsk town. This article provides the detailed description of the morphological structure of the Vorona river valley on the key site, parameters of macromeanders and palaeoreconstructions of river runoff, based on the parameters of the palaeochannels. Four levels of terraces and wide floodplain are presented in the studied part of the Vorona river valley. The river channel is meandering. The floodplain is predominantly segmental-ridged, complicated by numerous paleochannels. Among them, two generations are clearly distinguished in size – large paleochannels (macromeanders), in size many times larger than the parameters of the modern channel, and small paleochannels, corresponding in size to the modern channel. The width of macromeanders is on average 300–350 m; the width of small paleochannels is on average about 30–40 m. Large paleochannels are evidence of increased river runoff; their formation in this region is usually associated with the Late Glacial (18–12 ka BP). Small paleochannels are the same size as the modern river and were formed in the Holocene. The modern discharge of the Vorona river on the studied part of the valley is 37,9 m³/s, while the calculated values of the paleo-discharge (at which the macroradiations were formed) are 146,5 m³/s, that is almost 4 times higher. The modern runoff layer is 90 mm, the paleo-runoff layer is 350 mm.