R.S. Chalov

Types of river channel patterns and their natural controls

River channel patterns are thought to form a morphological continuum. This continuum is two-dimensional, defined by plan features of which there are three (straight, meandering, branching), and structural levels of fluvial relief of which there are also three (floodplain, flood channel, low-water channel). Combinations of these three categories define the diversity of patterns. One of the most important factors in channel development is stream power, defined by water discharge and river slope. The greater the stream power, the stronger the branching tendency, but threshold values of stream power are different for the three different hierarchical levels of channel relief. The critical stream power values and hydrological regime together define the channel pattern, and analysis of the pattern type can be undertaken using effective discharge curves.

Channel changes in largest Russian rivers: natural and anthropogenic effects

The aim of this paper is to provide comprehensive analysis of channel changes (horizontal and vertical movements of channel boundaries due to water flow and sediment transport interactions) in rivers across Russia. Evidences from channel transformations indicate that largest Russian rivers (Volga, Oka, Amur) are sensitive to mostly human impacts (reservoir construction, in-channel quarries, land disturbance and bank fortification). Channel changes in the Severnaya Dvina, Lena, Pechora and Ob Rivers over the past 100 years have been driven mainly by natural factors at the river scale, whereas some reaches were influenced by human interventions (including single reservoirs). Reservoir construction is probably the most extended influence on morphodynamics of the largest rivers of Russia, but the influence of other controls resulting in channel boundary movement and channel pattern changes could also be detected.

Sediment runoff, transporting capacity of flows and their role in river channel formation

An analysis is made of the sediment runoff as a determining factor of channel processes and as a set of phenomena arising due to the flow-channel interaction. The amount of sediments transported by the flow is determined by its transporting capacity that is changing constantly according to hydraulic characteristics of the flow undergoing changes across space and time. The relationships between them are responsible for the directedness of vertical channel deformations, i.e. incisions and accumulations of sediments leading to an increase or decrease in bottom elevations. In this case, the leading role in channel development is played by the runoff of entrained sediments. Its proportion governs changes in morphometric characteristics of the channel and its stability and influences the development of river branches and braids of the channel.

Experimental Study of Tidal Effects on Coastal Groundwater and Pollutant Migration

The problem of current urban groundwater pollution is very serious, which has influenced social development and people’s daily life. Around the land-sea interface, tide obviously changes nearshore the groundwater flow regime and makes the pollutant migration process become more complex. In the present study, the effect of tide-induced groundwater table fluctuations and on the pollutants migration in beach aquifers is investigated by constructing a two-dimensional sand trough physical experimental model. The model considered brackish-water density differences and the tide by controlling experimental medium properties and boundary conditions. The results showed that the groundwater table fluctuation cycle is the same as the tidal cycle and the fluctuation lag time increases linearly with the increase of the offshore distance. Tidal fluctuation flattens brackish-freshwater interface, widens the dispersion zone, and generates the upper saline and the freshwater belt. Time lag corresponding relationships between saline water and tidal fluctuation was observed. With the pollutant approaching the saline water area, the profile of the pollutant migration is gradually developed into a spindle shape until the strip shape, and the pollutant enters the saline water body along the curved edge of the upper part of the saline water. The transverse dispersion of pollutants is larger than the longitudinal dispersion in a tidal cycle and its outline presents a strip shape development. No mixing or exchange between the pollutants and the saline water body happened during the whole process. This study can provide scientific references for nearshore groundwater pollution prevention and control in the future.

Environmental and human impacts on sediment transport of the largest Asian rivers of Russia and China

The paper deals with comparative summary of sediment loads and particulate trace metals (V, Cr, Co, Cu, Zn, Cd, Pb) transport in the largest Asian rivers of Russia and China. Environmental conditions and human interventions in the selected catchments (Lena, Ob, Enisey, Selenga, Kolyma, Amur, Yellow, Yangtze, Pearl) are analyzed with respect to the rate and composition of suspended sediment loads. The paper presents calculations of sediment load changes at the downstream sections of the rivers and new database of the chemical composition of suspended matter which involves all recent studies of the last decade for the sediment geochemistry. The results indicate that fluvial system and its human modifications are the most significant drivers of sediment load. Fluvial erosion in the unconfined channels exerts a significant control on the sediment load changes due to observed permafrost melting. We concluded that construction of reservoirs has the most important influence on land–ocean sediment fluxes in the largest rivers of Asia but plays relatively weak role in heavy metal composition in suspended particulate matter (SPM) due to lowest sedimentation rates of the fine clay particles, which are mostly enriched with heavy metals. The paper also presents novel mapping approaches related to cartographic recognition of the fluvial system and its human modification and sediment transfer processes in the largest Asian rivers of Russia and China, linked with a specific legend. Finally, analysis of uncertainties associated with estimating the SPM composition in the rivers was done with respect to spatial and temporal variability. It was shown that the main error occurs due to incorporation of data only from particular hydrological seasons which usually ignore high flood conditions.

Spatiotemporal variability in channel deformations on rivers of Russia

We assess the spatiotemporal changes in channel processes on rivers of Russia, determine the causes for vertical (incision or directional sediment accumulation) and horizontal (displacement of channel forms) deformations and show the distribution of stream channel of different morphodynamical types and with a different reconfiguration rate. The conditions are revealed, under which the channel types change over time. Particular emphasis is placed on the analysis of spatiotemporal changes in channels caused by anthropogenic disturbances and by direct technogenic interferences in the life of rivers (hydroelectric schemes, quarries in the river channels, and waterway dredging).