Estimating Annual Volga Runoff in the Late Glacial Epoch from the Size of River Paleochannels
Aleksey Sidorchuk, V. Yu. Ukraintsev, А. В. Панин
Abstract
Large paleochannels, which are common in the floodplains and terraces of rivers in the Volga Basin, are indicators of an appreciable increase in river flow in the past and can be used to evaluate the paleodischarges of water using morphometric relationships. The study develops the procedure proposed earlier for evaluating the paleorunoff. An improved procedure is used to evaluate the runoff in the period when large paleochannels were forming (18–13 thousand years ago) for more than 120 small basins. Areal interpolation was used to map the annual paleorunoff depth in the Volga Basin. The reconstructed field of river runoff in the Late Glacial Period shows zonality similar to that one can see now: the maximal runoff depth (from 450–550 mm) was recorded in the Upper Volga and in the upper part of the Kama Basin, and the minimal runoff depth (100–200 mm), in the Lower Volga. In large parts of the Volga Basin, the runoff was 1.5–1.9 times greater than its present-day value. The annual runoff for the entire Volga Basin was evaluated at 420 km3. This volume is enough to keep the Caspian level at elevations of the maximum of Khvalynskaya transgression (~+48 m abs.), provided that the effective evaporation (evaporation less precipitation) in the water area was one quarter less than its present-day level (~550 mm with the possible glacier runoff not taken into account and~600 mm with it).