Improvement of the method of combined plans for the analysis of channel re-formations of a water body on the example of the oka river section

The article discusses the ways of improving the method of combined plans for a water body channel reformations analysis on the example of a section of the Oka River. The main disadvantages of the existing classical approach to the analysis of channel processes through the channel surveys separate isobaths’combination are highlighted. A new approach to combining digital models of the river bed relief obtained from the hydrographic surveys results is proposed. Two directions of surface comparison are shown for the subsequent analysis of channel processes. For a qualitative assessment of channel changes, it is proposed to construct a new surface of vertical deformations and visualize it in color gradation or using lines of equal vertical deformations. For a quantitative assessment of channel processes, the use of a cartogram of vertical channel deformations is considered, and the numerical parameters for assessing the stability of the river channel are introduced. For the considered section of the Oka river channel, the main indicators of channel processes were obtained and analyzed using the proposed updated method. Separately, the calculation of the most optimal grid size was performed when constructing a cartogram of vertical channel deformations.

Sediment Transport and Water Flow Resistance in Alluvial River Channels: Modified Model of Transport of Non-Uniform Grain-Size Sediments

The paper presents recommendations for using the results obtained in sediment transport simulation and modeling of channel deformations in rivers. This work relates to the issues of empirical modeling of the water flow characteristics in natural riverbeds with a movable bottom (alluvial channels) which are extremely complex. The study shows that in the simulation of sediment transport and calculation of channel deformations in the rivers, it is expedient to use the calculation dependences of Chézy’s coefficient for assessing the roughness of the bottom sediment mixture, or the dependences of the form based on the field investigation data. Three models are most commonly used and based on the original formulas of Meyer-Peter and Müller (1948), Einstein (1950) and van Rijn (1984). This work deals with assessing the hydraulic resistance of the channel and improving the river sediment transport model in a simulation of riverbed transformation on the basis of previous research to verify it based on 296 field measurements on the Central-East European lowland rivers. The performed test calculations show that the modified van Rijn formula gives the best results from all the considered variants.

TRANSFORMATION OF FLOODPLAIN LANDSCAPES UNDER THE INFLUENCE OF NATURAL AND ANTHROPOGENIC CHANGES IN THE ENVIRONMENT (ON THE EXAMPLE OF THE ZAKHARKOVO FLOODPLAIN OF THE MOSCOW RIVER)

The Zakharkovskaya floodplain of the Moscow River is located directly above the Moscow Ring Road. It is an example of a natural structure that is spontaneously restored after long-term economic use (hayfields, pastures, long-term plowing, summer cottege settlements, drainage and irrigation channels, silt sites, etc.) under conditions of cessation of intensive anthropogenic impact. The article deals with the history of the formation and development of the Zakharkovskaya floodplain in prehistoric times (late Holocene), in the early historical period (beginning-middle of the second millennium AD), and in the late historical period-XIX-XXI centuries. The regulation of water flow, which has occurred in recent decades, is accompanied by a relative stabilization of the Moscow riverbed, turning it into a canal, reducing the intensity of channel deformations, leveling the bottom relief with its general deepening. As in other floodplain plots, the territory of floodplain leaves the flood zone; depressions are filled in, lakes are degraded, and man-made terrain is formed. At the same time, the current restrictions on access to the territory of the Zakharkovskaya floodplain for 10-15 years have created conditions for the restoration of natural structures, in particular, forest and shrub tracts, and increased the landscape and ecological attractiveness of floodplain lands.

UNCERTAINY OF THE RIVER’S BASELEVEL (ON THE EXAMPLE OF THE LOVAT RIVER)

Studies of channel deformations are important for the design of hydraulic structures on rivers. Deep deformations in the lower reaches can theoretically not exceed the baselevel. The aim of the work was to determine the baselevel of the Lovat River and compare it with the elevation marks of the river bottom.

Simulation of the meander cut-off by 2D hydrodynamic model for erodible bed

<p>The retrospective simulation of the Pyoza river (Arkhangelsk region, Russia) meander cut-off in 2003-2008 has been undertaken. As a result of the river bend straightening two large villages were cut off from the road network of the region.</p><p>The initial data for modeling were obtained by analyses of archive satellite images for the period from 1997 together with the runoff data, as well as by the field survey of September 2019. The simulation was performed by the latest version of the STREAM_2D CUDA software, using a new method for the numerical solution of two-dimensional Saint-Venant equations [1]. It was adapted for the complicated bottom topography typical for a wide floodplain with a meandering channel flooded in high water stage.</p><p>The mass-exchange equations for three layers of sediment over the unerodible bed were solved together with the hydrodynamic equations. When calculating channel deformations, the gravitational effect due to bottom slope and the influence of secondary currents on the sediment shift were taken into account [2].</p><p>The Pyoza river is the lowest large tributary of the Mezen’ river flowing into the White sea. It is distinguished by a typical alluvial channel, meandering along wide floodplain composed by sands and sandy loams. The maximum runoff usually corresponds to spring snow-melting and can reach 1500-2000 m<sup>3</sup>/s.</p><p>To schematize the computational domain of the Pyoza river section of 13 km long, a hybrid grid of irregular structure was constructed, consisting of 37 329 cells of a quadrangular shape for the channel and a triangular one for the floodplain.</p><p>The simulation started at the year 1997 when where was no any rill across the meander neck. The time step of calculation was taken to be one day.</p><p>Modeling made it possible to simulate realistically the essential steps and mechanisms of the meander cut-off: the development of a pioneer straightening rill, its widening and deepening, as well as blocking of the old channel by a point bar in its upper reaches, as well as its further silting and aggradation.</p><p>1. Aleksyuk A.I., Belikov V.V. (2017): Simulation of shallow water flows with shoaling areas and bottom discontinuities. Computational Mathematics and Mathematical Physics, Volume 57, issue 2, pp. 318–339. https://doi.org/10.1134/S0965542517020026</p><p>2. Aleksyuk А. I., Belikov V. V., Borisova N. M., Fedorova T. A. (2018): Numerical modeling of non-uniform sediment transport in river channels. Water Resources, Volume 45, Special Issue S1, pp. 11–17. http://dx.doi.org/10.1134/S0097807818050275</p>

Modeling of channel processes in large rivers with the use of field data

The paper deals with mathematical description of channel processes occurring in long sections of large rivers with a complex morphometry. To forecast negative manifestations of channel deformations, a computer model of river sediment transport in the study section is proposed. It is based on a three-dimensional (3D) / two-dimensional horizontal (2DH) flow model, a 2DH model of bed sediment transport and observation data. Comparative analysis of simulation results of channel processes in the Ob river section at the Barnaul water intakes and in situ data makes it possible to evaluate forecast capabilities of the designed model, in particular, for quantitative assessment of changes in channel topography of the study section caused by natural and anthropogenic impacts.

Application of the method of mathematical modeling for forecasting channel deformations at the underwater crossing of the main pipeline

In order to determine the possibility of using the method of mathematical modeling for making long-term forecasts of channel deformations of trunk line underwater crossing (TLUC) through water obstacles, a methodology for performing and analyzing the results of mathematical modeling of channel deformations in the TLUC zone across the Kuban River is considered. Within the framework of the work, the following tasks were solved: 1) the format and composition of the initial data necessary for mathematical modeling were determined; 2) the procedure for assigning the boundaries of the computational domain of the model was considered, the computational domain was broken down into the computational grid, the zoning of the computational domain was performed by the value of the roughness coefficient; 3) the analysis of the results of modeling the water flow was carried out without taking the bottom deformations into account, as well as modeling the bottom deformations, the specifics of the verification and calibration calculations were determined to build a reliable mathematical model; 4) considered the possibility of using the method of mathematical modeling to check the stability of the bottom in the area of TLUC in the presence of man-made dumping or protective structure. It has been established that modeling the flow hydraulics and structure of currents, making short-term forecasts of local high-altitude reshaping of the bottom, determining the tendencies of erosion and accumulation of sediments upstream and downstream of protective structures are applicable for predicting channel deformations in the zone of the TLUC. In all these cases, it is mandatory to have materials from engineering-hydro-meteorological and engineering-geological surveys in an amount sufficient to compile a reliable mathematical model.

CHANNEL DEFORMATIONS FORECAST AND FEATURES OF FLOODPLAIN QUARRIES OF NON-METALLIC CONSTRUCTION MATERIALS DEVELOPMENT IN MEANDERING RIVERBEDS BASED ON SAFE NAVIGATION CONDITIONS (ON THE EXAMPLE OF THE BELAYA RIVER)

Floodplain quarries of non-metallic construction materials (NCM) have a minimal impact on the water regime and navigable conditions of the reservoir in the area of their location. However, the development of such deposits has its own characteristics, especially in case of their location in meandering beds of large navigable rivers. On the example of floodplain quarry located at the mouth of the Belaya river (1757-1763 km), development conditions for such facilities based on ensuring navigation safety were considered; on the basis of changes’ dynamics in the bends’ main parameters the channel state assessment and fluvial deformations forecast were made. It was concluded that it is possible to extract sand and gravel in the studied section of the Belaya river, provided that navigation safety issues are resolved in a comprehensive manner. First of all, it refers to meander straightening and transferring the ship's course to a new capital slot.

BASIC LAWS AND LOCAL FEATURES OF DEVELOPMENT OF SMALL AND MEDIUM-SIZED RIVERBEDS (results of monitoring observations)

The article describes the results of monitoring of stream-bank erosion on small and medium-sized rivers of Central Russia - the wide-bottomed Kerzhents and Sherna and the narrow-bottomed embedded Tarusa. It was found that horizontal channel deformations generally occur according to the expected patterns: erosion of concave banks of bends, alluvium of their convex banks, curvature and then straightening. However, both on medium and small rivers, local non-fluvial factors interfere with this process, disrupting the interaction of the flow and the valley floor, bringing elements of unpredictability to typical channel deformations. This is especially noticeable on embedded rivers that lack a wide floodplain - a natural buffer that protects the channel from the effects of slope and other processes occurring on the slopes and in the near-valley parts of the watersheds.