FEATURES OF HYDRAULICS OF THE RIVER SECTORS WITH RIVERBED WINTERING HOLES OF THE IRTYSH IN OPEN WATER PERIOD
The article describes features of the hydraulics of the Irtysh riverbed in the sections of significant fish concentrations -wintering holes - in the open water period. There have been explored the waters of the largest (in area and in depth) Gornoslinkinskaya and Kondinskaya riverbed depressions located in the Uvat and Khanty-Mansi districts of the Tyumen region and Khanty-Mansi Autonomous District, respectively. The bathymetric characteristics of wintering holes were studied using computerized hydroacoustic complex AsCor (Promgidroakustika, Ltd., Petrozavodsk). To create the bottom relief of riverbeds there were used geographic information software programs Surfer 9.0 and Map Viewer 6.0. The study of the species composition of the fish population was carried out conducting control catches with stationary and drift nets. It has been found that, as a result of the combination of features of the riverbed, on the investigated sectors there is formed a complex hydrodynamic and turbulent environment. The holes are located on meanders with coefficients of high curvature of the bend of a channel, there have been found the ranges with narrowing channels at the entrance into the turn. In the process of the channel narrowing there occurs deepening of dynamic river flow axis and eroding of the bottom, which may prevent silting of the wintering holes. Significant differences in the depths cause a compensating current. Due to the bend of the riverbed in the water areas there are formed whirlpool zones, and arising transverse water currents close the surface and bottom streams of the river flow. The heterogeneous hydrodynamic environment of the Kondinskaya depression is complicated by the fact that the Konda flows into the bend of the Irtysh; as a result, there takes place an exchange of river impulses. Thus, when the longitudinal flow velocity is imposed on the transverse flows, there appears a spiral movement of the water masses and vertical vortex structures - whirlpools resulting in optical (turbidity) and turbulent (hydrodynamic) heterogeneity in the water column of the riverbed wintering holes.