River-bed Processes Research Articles

Оценка параметров руслового процесса в условиях изменения гидравлического режима

Introduction. The authors address the development of river bed deformations under the influence of a water flow in conditions of a changing hydraulic regime and scroll-bar riverbed processes. The relevance of the publication is explained by the unavailability of reliable waterbed shape forecasting methods needed to ensure their normal ecological condition. Meanwhile, the analysis of the motion of solid particles is associated with the sediment flow rate at the level of saltation, and with hydraulic friction losses at the level of microforms. New dependences are proposed for the sizes of bedforms, depending on the parameters of a streamflow. Materials and methods. The influence of factors in the form of new dependencies has been proven on the basis of the study of recent and classical research works, an experimental study of the formation and development of the bottom relief in case of a change in the hydraulic regime of the streamflow. Results. The author has studied the reasons and conditions for the formation and development of bedforms at the initial stage of interaction between the flow and the riverbed, as well as the factors influencing the formation of the bottom relief which is initially smooth. Structural levels of the waterbed evolution process have been analyzed. The experimental data were analyzed to identify a universal correlation between the flow parameters and the height of the developing bottom microrelief elements, from which the resistance formula is derived that coincides with the Knoroz dependence for steepness of bedforms that complies with the Boussinesq dependence. Conclusions. The results of this study can be used to prognosticate the riverbed evolution process in case of changing hydraulic regimes of water flows in the waterbed, composed of erodible soil not only at the initial stage of formation of bedforms, but also in the course of the bottom relief development.

ИЗУЧЕНИЕ ПЕРЕФОРМИРОВАНИЯ БЬЕФОВ НИЗКОНАПОРНЫХ ГИДРОУЗЛОВ В НИЗОВЬЯХ РАВНИННЫХ РЕК

The article presents the results of long-term field studies of the re-formation of water courses in the zone of the Takhiatash hydroelectric complex. It was noted that due to low water, for a significant part of the year, the Takhiatash dam worked with fully closed gates in all spans. In these years, the role of regulating the level regime of the shield dam is almost lost, and the end regulators of the main channels are regulated.
 The data of comparison of actual expenses, turbidity and back-up at the Takhiatash hydroelectric power plant with the calculated ones are presented. It is proved that sharp fluctuations in the water level in front of the dam and water intake into the channels lead to changes in the hydraulic and alluvial regime of the shield dam and channels. As the analysis of the survey of the riverbed cross-sections in the headwaters of the Takhiatash hydroelectric complex showed, in the initial period of operation, the bottom marks in the upper stream are increasing and the bottom marks in the lower stream are decreasing. Further years of operation (after 1982) were characterized by the stability of the flowing riverbed processes, that each characteristic year has its own level and consumption regime. It is noted that in high-water years there were no difficulties with water intakes, and the main difficulties are associated with the passage of flood flows through the shield dam. In recent years, there has been a rapid rise in the water level in the upper reaches, despite all the open dam gates, shipping locks and water intake structures, which are explained by the influence of the drifted streams on the capacity of the shield dam. It is proved that without any damage to the water intake during the growing season, it is possible to effectively flush the upstream with a constant decrease in the water intake coefficient - Kv < 0.55. Practically, this means for the Takhiatash hydroelectric unit that the flushing flow rate should not be lower than Q ≥ 250 – 300 m3/s.

Hazards of riverbed processes in Russian rivers: Evaluation criteria, mapping and regional analysis

The danger of riverbed processes is considered. Their speed varies from the first few months of the flood to the most dynamic process in nature. It happened in front of people. This may make life on the river bank and the utilization of river resources more difficult. This paper introduces the causes and consequences of the danger performance of riverbed processes, and focuses on the mapping methods of the danger assessment of riverbed processes: determining the danger degree of riverbed processes and different methods of displaying it on the map. An example of displaying danger on the previously drawn map is given, and the distribution of different types and expression degrees of dangerous riverbed processes under various natural conditions in Russia is briefly analyzed.

ОПАСНОСТЬ РУСЛОВЫХ ПРОЦЕССОВ НА РЕКАХ РОССИИ: КРИТЕРИИ ОЦЕНКИ, КАРТОГРАФИРОВАНИЕ, РЕГИОНАЛЬНЫЙ АНАЛИЗ

The article discusses the danger that channel processes – the processes creating the river channel and floodplain and those occurring in them – can pose to people. Riverbed processes are among the most dynamic ones in nature: the speed of their manifestation varies from the first decades to individual months in high water and floods, i.e. they develop in full view of people. This can significantly complicate life on the banks of rivers and the use of river resources. The article deals with dangerous manifestations of riverbed processes, their causes and consequences, but the main part of the paper is devoted to the cartographic method of assessing the danger of riverbed processes: determining the danger degree and various ways of displaying it on maps. There are given examples of showing danger on previously compiled maps. In conclusion, the article provides a brief geographical analysis of the distribution of various types and the manifestation degree of dangerous riverbed processes in a variety of natural conditions in Russia.

Studies of turbulent flow characteristics of dividing open water streams

The movement of water in the areas of division of open streams has a particularly turbulent character. For a detailed study of river bed processes, it becomes necessary to identify the patterns of turbulent motion [1]–[29].The aim of these studies was to study and determine the turbulent characteristics of the flow and to establish the relationship between the intensity of flow turbulence with the channel deformations observed.Theoretical and experimental research methods, laboratory studies, field surveys of existing water intake units were used. When processing the results of experimental studies, the methods of mathematical statistics were used.On a specially constructed hydraulic model, detailed experimental studies of the flow structure in the fission unit were carried out under conditions of rigid and eroded channels. [3], [28], [29].Detailed studies have revealed the kinematic structure of the flow in the section of flow division.The nature of the change in the intensity of the turbulent characteristics of the flow in different sections of the fission unit in rigid and eroded channels is determined.The relationship between the nature of the change in the flow turbulence intensity and the channel deformations observed in the division unit has been established.

Studies on the threshold density of Phragmites australis plant concentration as a factor of hydraulic interactions in the riverbed

The paper features the results of numerical analyses and field survey concerning the density threshold for concentration of Phragmites australis plants in the aspect of its impact on hydraulical flow conditions in the river. Simulations were performed for a typical vegetation concentration mapped from representative natural rivebed of Sleza River (Lower Silesia/Poland). The numerical model was constructed, which was calibrated on the basis of field survey conducted with use of hydrometric current meter and an acoustic Doppler current profiler (ADCP). For given fixed spatial configuration (of the area) of analysed riparian plant community, in numerical model, the community density was altered by i.a increase of stems distribution density. Such boundary measure of plant concentration (density) was sought, that after it is exceeded, the flow through the plant community is negligibly small in comparison to dominant stream circumfluenting the plant „obstacle”. The analysis was also conducted on variable and dependent on vegetation density hydraulic interactions between the vegetation zone and water stream in river. Knowledge of boundary density for particular vegetation species in riparian zones can be used in ecological engineering, especially in proecological river regulation. The conservation practices can be performed in the riverbed that allow to keep vegetation communities, interfering only its density and by that there is an opportunity to control the riverbed processes.

Problems of riverbed evolution in the basin of the Ural River

Aspects of riverbed evolution including bank erosion in the Ural River basin have been considered in this paper. The natural morphodynamic types of riverbeds have been described. The spatial features of their genesis have been characterized within the Ural River basin. To study the riverbed processes, decoding of remote sensing data of the water surface has been used. The risks for the infrastructure facilities and for the residential districts have been analyzed in terms of the bank erosion in the Ural River basin. The issues concerning the border between the Russian Federation and the Republic of Kazakhstan due to riverbed reconfiguration of the Ural River have been outlined. Maps of the development of bank erosion in the Ural River basin have been created. A way to solve the problem of riverbed evolution along the border area has been proposed by organizing an Intergovernmental Specially Protected Natural Zone.

Effects of biofilm on river-bed scour

Biofilm acts stabilising river-bed sediments, interfering with particle entrainment and, consequently, preventing bed disturbance. In this paper we present the results of a series of experiments carried out in indoor channels, aimed to understand biofilm alteration of bed material motion and topographic changes in stream channels. We analysed the erosion patterns and bedload rates in non-cohesive sediments in channels colonised by biofilms and compared them to biofilm-free others. All the channels had the same conditions of light irradiance, temperature, slope, and particle size (sand). Discharge and water surface slope were modified to create a range of hydraulic conditions, with pairs of colonised and non-colonised channels subjected to the same flows. We observed that biofilm slightly modified bed roughness and flow hydraulics, but that highly influenced bed disturbance. Biofilm caused bed scour to occur in patches unevenly distributed along the channel length, as a result of localised weaknesses of the biofilm. Once biofilm was ripped up it was transported in chunks, and sand grains were observed attached to these chunks. In non-colonised sediments the erosion was more homogeneous and the formation and movement of bedforms were observed. On average, bedload rates were 5 times lower when biofilm was present. Overall, the protective effect of the biofilm prevented generalised erosion of the channel and delayed the entrainment and transport of sand grains. Results emphasised the important role of biofilm in the incipient motion of bed-material in stream channels; this role may affect the magnitude and frequency of subsequent river bed processes, notably the onset of bedload and associated channel morpho-dynamics.

GEOGRAPHICAL RIVER-BED STUDY AND RIVER-BED MORPHODYNAMIC

The justification of the geographical river-bed study as substantive research field is founded. The structure of this study is under consideration. Special attention is paid to its component - river-bed morphodynamics that deals with river-bed morphology, river-bed deformation and water regime, technogenic changes of river-bed processes and forms, hydromor-phological interrelations between river-bed forms parameters and factors of river-bed processes. The connections of riverbed morphodynamics with flood-plane study, longitudinal profile theory, and studies of factors and conditions of river bed processes.

Dynamics of river bed processes of the Ural River in Western Kazakhstan

A retrospective analysis of river bed deformation over a 34-year period has been carried out for the first time for the Ural River in West Kazakhstan, in different environmental conditions. Horizontal shifts of the Ural riverbed have been defined according to space shots made in 2012. Erosion risk, as a result of horizontal displacement of the river bed has been determined in West Kazakhstan. A geomorphologic description of the Ural River bed and floodplain, and the dynamics of channel processes in the river within West Kazakhstan are given. The probable pattern of channel realignments for the Ural River has been determined. The paper describes the results of map compilation and related data consolidation with respect to the horizontal river bed shifts in West Kazakhstan, and includes a review of characteristics of the hydrologic and hydrochemical regimes of the river. The main river bed types, which are typical of flat terrain, are also discussed. West Kazakhstan is a region where there is medium-level ecologic stress on the river beds and floodplains.

Elucidating the nature of surface water - groundwater interactions beneath a large unregulated river system with the aid of AEM data

The Fitzroy River with its associated alluvial aquifer in northern Western Australia has been considered in planning for Perth?s future water supply and for agricultural development but its potential needs to be informed by detailed understanding of groundwater-surface water interactions occurring along its extent, and in particular must consider and account for the consequences that might arise when extracting groundwater from shallow and deep aquifers linked to this river system. Results from the interpretation of a regional scale longitudinal transect (~274 line kms) of SkyTEM helicopter EM data are presented which elucidate river-bed processes occurring along its extent. The AEM indicate a variable groundwater quality and related aquifer characteristics associated with different parts of the river. A 1D laterally constrained inversion (LCI), was examined against hydrochemical, environmental tracer (including 222Rn and Cl-), and hydrogeological data sampled longitudinally. Combined, they indicate a link between the Fitzroy?s alluvial aquifer system and with underlying Canning Basin sediments. The results demonstrate the value of regional, reconnaissance scale AEM surveys to better define groundwater processes beneath large unregulated river systems.

Ice-rock avalanche of 2002 in Genaldon River valley, North Caucasus, Russia: consequences and problems

The biggest glacial disaster in the Russian history occurred in September 2002. A huge ice- rock-water flow from the Kolka Glacier went down the Genaldon River valley with a speed of 320 km/h. Having travelled a distance of 18.5 km, it was stopped by the 2 km long narrows of the Rocky Mountain Range and it filled the hollow with 120 ml of deposits. The ice­ rock-water mass pressed through the narrows forming a debris flow which went down the valley for 10 km devastating all the settlements on the riverbed. As a result, 125 people lost their lives. In 2002, two months before the disaster, a series of collapses from an elevation of about 1000 m at the backside of the glacier had activated the avalanche. The last ice- mass collapse had a volume of 10 million ml. The material accumulated in the glacier hollow was knocked off and went down the valley. The 100-150 m high ice- rock- water mass (with air also) was moving down the 400- 500 m wide valley. The flow on its way down the valley trough was fed by the frontal masses of three huge ancient landslides situated on the left bank. The hazards and risks after 2002 can be attributed mainly to the filling up of the hollow by the ice-rock material, the formation of a dammed lake, and the filling up of the narrows by debris flow and mudflow deposits. Presently the dammed lake is discharging naturally and there is about 0.5 million ml of water in it. The future behaviour of the ice-rock dam is not clear and it is difficult to make any forecast due to its melting on the one hand and the formation of underground outflows with sporadic floods on the other hand. In 2002-2004 the debris flow deposits on the riverbed were still unstable and loose. A surge with a discharge of more than 20 m3/sec and (or) a storm flood of such a magnitude can adversely affect the riverbed processes in the overpopulated foothill areas requiring mitigation and protective measures.

River energy budgets with special reference to river bed processes

River energy budgets with special reference to river bed processes

River energy budgets with special reference to river bed processes

This paper uses detailed hydrometeorological data to evaluate the influence of channel bed processes on the river energy budget at an experimental site on the regulated River Blithe, Staffordshire, UK. Results from a pilot study are presented for eight days during July, September, October and November 1994. Total energy gains were dominated by net short-wave radiation (97·60%) with significant contributions from sensible heat exchange and friction (1·17 and 1·06%, respectively) and minor additions from condensation and bed conduction (0·16 and 0·01%, respectively). Net long-wave radiation, evaporation, conduction into the river bed, sensible heat transfer and the energy advected during evaporation accounted for 53·98, 23·56, 16·27, 5·25 and 0·94% of the total heat losses. On average, over 82% of the total energy transfers occurred at the air–water interface. Approximately 15% of the total energy exchanges occurred at the channel bed, but maximum daily heat exchanges accounted for up to 24% of the daily total energy transfer. The amount of short-wave radiation attenuated in the water column, and values measured at the channel bed varied considerably from those calculated using a standard coefficient. Values of bed conduction varied in response to different vertical thermal profiles in the channel bed, reflecting the variable influence of sedimentology and groundwater flux. Fluctuations in levels of periphyton and macrophyte cover were also shown to have a significant effect on energy fluxes at the channel bed. © 1998 John Wiley & Sons, Ltd.

Operating difficulties at the maikopsk hydroelectric station caused by scouring in the lower pool

1. When designing and operating retaining structures on rivers carrying heavy sediment loads and flowing in unstable channels, it is necessary to take into account possible consequences of the accumulation of sediment in the upper pools and possible river-bed processes in the lower pools which can lead to a deterioration in the operating conditions of the turbines and hydraulic structures. 2. Depending on the extent of expected channel deformations, measures should be taken to maintain the level in the lower pool at the prescribed elevation.

Investigations by specialists in the USA in the Area of bed-load movement and river-bed processes

Investigations by specialists in the USA in the Area of bed-load movement and river-bed processes

Conference on Problems of Water Intakes and River-Bed Processes

Conference on Problems of Water Intakes and River-Bed Processes