SEDIMENT BUDGET OF THE OB' AND THE YENISEI

Introduction:

For today it is unclear what are quantitative estimates of sediment budget components for big rivers such as the Ob’ and the Yenisei. Thus, in this investigation, we developed the methodology to esteem the main components of sediment budget, such as bank and watershed erosion, total annual sediment yield, and total deposition, based on field measurements at the ends of the rivers and modeling.

Methods and results:

1. For calculation of total sediment load was developed the program (language R), based on usage of extrapolated ADCP measurement data, in particular, water velocity and backscatter intensity. The average annual sediment runoff for the Ob' was esteemed as 63.5 Mt/year, for the Yenisei 32.5 MT/year;

2. The watershed component of sediment runoff calculated by the RUSLE, taking into account the trapping of sediments by reservoirs and lakes. For the Ob' potential watershed erosion is 85 MT/year and for the Yenisei 53.6 MT/year.

3. The bank erosion was calculated based on remote sensing databases, such as GSWE, Arctic-DEM, HYDROATLAS, and GRWL. For the downstream of the rivers, we got 35.0 MT/year for the Ob and 21.9 MT/year for the Yenisei.

4. The total deposition of sediments was calculated as a difference between total sediment yield and total erosion in catchments. For the Ob' total deposition was 56.5 MT/year, for the Yenisei 43 MT/year.

Discussion and conclusion

The sediments deposited at slopes or as bedforms can be eroded again by snowmelt and rainfall erosion or due to the bank erosion. The products of erosion gradually move to the end of the river, except the part of sediment that trapped by reservoirs. For example, for the Ob', it is only 10% of the watershed erosion, and for the Yenisei, it is 17% of eroded soil on the catchment. According to the calculations, bank erosion for both downstream is less than the watershed component of sediment runoff that can be delivered to the estuary, but the interesting fact is that bank and watershed erosion estimates are comparable for the big rivers.

Acknowledgments

This work powered by the grant №18-05-60219 of Russian Foundation for Basic Research(RFBR)