The hydromorphological situation at the site of bridge construction is analyzed in the paper; the analysis results are presented. The issues of ensuring the channel geometry stability are considered. The impact of a temporary construction embankment on the f low kinematics is estimated. The level regime of the river and the channel reformations in the alignment of the bridge crossing and on the upstream section of the river are studied at the calculated level and water flow. The results obtained make it possible to determine and establish the values of the permissible degree of impact of the designed hydraulic structures and measures on the channel regime of the near-mouth section of the Zeya River in the area of the projected bridge crossing over the river in Blagoveshchensk, within which the natural and anthropogenic-induced conditions of the statistical stability of the “flow-moving channel” system are realized by the river flow. The studies were carried out in 2 stages: the first one, a test stage, was carried out for the initial everyday state of the riverbed in the section of the Zeya River in the area of the bridge crossing, according to which the model was calibrated in accordance with the specified boundary conditions in the area under study; the second one, on the model, was carried out for three options of the construction dam length, erected from the left bank to the 15th pillar of the bridge, to the middle of the span between the 15th and 16th pillars and up to the 16th pillar of the bridge crossing, which made it possible to assess the impact of the structure with different options of its length on the flow hydraulics in the area of the bridge crossing. The research method applied is the mathematical 2-D modeling of the water movement characteristics, for which the “FLOOD” software package is used.

At present, in practice, to model channel reformations in rivers with a deformable bottom, a large number of different formulas are used to calculate the flow of bottom sediments. However, the reliability of channel forecasts performed using the apparatus of mathematical modeling, in most cases, still remains quite low. The quality of channel forecasts performed when designing engineering measures to ensure navigation on rivers is determined, on the one hand, by the correct assessment of the physical nature of sediment transport in natural channel flows, and, on the other hand, by the quality of the applied numerical models. This work is devoted to the verification of the sediment transport model based on studies in hydraulic flumes, in which microforms and mesoforms of a river channel with a secondary type of channel process were simultaneously reproduced. Such problems have not been considered yet. The previous experiments were carried out with a uniform steady-state mode of water movement at one structural level of bottom sediment movement - with the movement of bottom sediments in the form of microforms (dunes) - i. e. on a flat day. The results obtained in the course of the research make it possible to obtain new data, using which it seems possible to improve the quality of modeling of sediment transport in natural channel flows. This line of research, based on the use of the methodology for calculating the discharge of channel sediments using the parameters of dunes, can objectively lead to an increase in the reliability of forecasts of channel reformations when keeping navigation on free and regulated rivers with a moving bottom.