THE MAIN REGULARITIES OF THE RATIO BETWEEN RIVERBED AND BASIN COMPONENTS OF EROSION AND SUSPENDED SEDIMENT FLUX IN THE NORTHERN EURASIA’S RIVER BASINS

Abstract

Suspended sediment flux is one of the objective and sufficiently accurate measures of the erosion activity in basins. Using the database for mean monthly values of water and suspended sediments runoff created for 460 rivers of the territory of the former USSR, the ratio of channel and basin components of erosion was analyzed. For this purpose the author proposed the special hydrological method (published early). For all analyzed river basins the share of riverbed erosion (δr) calculated by suspended sediment fluxes doesn’t exceed 15%. It amounts to 10.4±1.5% for the plain (lowland) rivers, to 4.9±0.9% for the low-altitude mountain rivers, and to 4.0±0.8% for the middle-altitude mountain rivers. The average δr for the whole Northern Eurasia is 7.2±0.8%. The ratio of channel and basin (δb) components depends distinctly on the landscape-climatic conditions, especially on latitudinal zoning. Thus, within the plains of Northern Eurasia the biggest δr occurs in the zones of tundra, taiga and mixed forests – more than 15–16% (15.0±9.6% in the tundra zone, 16.6±3.1% in the zone of taiga and mixed forests). In arid zones this value on the average does not exceed 5% (4.5±1.3 % in the steppes, 0.8% in the semi-deserts). Intermediate areas have a share of channel products of 5 to 10% (8.9±2.0% in the zone of broad-leaf forests, 5.2±1.6% in the forest-steppe zone). The same trend is observed in the low mountains but less distinctly than in the plains. There is a hyperbolic relationship between a total suspended sediment flux and its riverbed component. This dependence is clearly pronounced in the plains of the Northern Eurasia, but diminishes with increasing elevation of river basins. It’s shown also that the lithological factor (surface rocks’ composition) doesn’t play a significant role in the spatial variability of the δb/δr ratio.