Environmental assessment of the estimated dredging volumes on the Ob River

The object of the study is the impact of dredging in the Ob riverbed on individual components of the environment, in particular, ichthyofauna. The volumes of transit and capital dredging in the river channel on the crossing sections that are difficult for navigation have been determined and substantiated. To calculate the damage, a method to determine the loss of ichthyofauna was used, taking into account the death of benthic and planktonic organisms in turbidity plumes and on the bottom areas subjected to development by dredgers and buried under dumped fills. It has been established that the greatest losses of ichthyomass will occur in the sections of the Upper Ob (up to the Novosibirsk reservoir) and the Middle Ob (up to the mouth of the Tom River), which is explained by the presence of numerous crossovers that impede navigation and require constant dredging. In the Lower Ob, the negative impact on benthos, plankton and ichthyofauna will be insignificant due to the small number of small crossovers. The volumes of dredging in the fairway required to maintain guaranteed depths and dimensions have a certain environmental load, the level of which is not critical for the ecosystems of a large river. However, when creating large-scale capital bypass channels, it can increase sharply in certain years. By reducing the load, a stable shipping lane can be created and the frequency of dredging operations at each of the crossover sections can be reduced. The advantages and disadvantages of the used damage assessment method are noted.