Vol 51, No 5 (2024)

Based on stationary and expeditionary hydrological data and information about the water management complex and volumes of water use, we have calculated for the first time the minimum permissible, average, and optimal hydrographs (in monthly increments) of the influx of Ural waters from Russia to the West Kazakhstan and Atyrau regions, which would not limit the functioning of the main participants of the Kazakhstan water management complex, would not deteriorate the quality of life of the population and existence conditions for aquatic and near-water biocenoses, and would preserve the river as a hydrographic object. The resulting hydrographs summarize (1) the values of current and future water consumption in the cities of Uralsk and Atyrau and numerous rural settlements, as well as water intake by irrigation and water supply canals, including the Kushum Canal; (2) the needs of river navigation for controlling depths and continuous navigation from May to October; (3) the environmental flow necessary for the reproduction of sturgeon fish species and the preservation of the bioproductivity and biodiversity of floodplain ecosystems. The latter element required nonstandard solutions, including those based on the existing domestic approaches to determining critical and optimal values (with respect to floodplain–channel ecosystems) values. Another and completely new result of this research is analysis of the long-term dynamics of maximum and minimum levels in the lower reaches of the Ural River and the frequency, duration, and depth of floodplain flooding

The spatially distributed ECOMAG runoff formation model was used to calculate physically based changes in the water regime in the Ural River basin in the XXI century with the use of data of an ensemble of Earth system models and scenarios of anthropogenic impact on the climate system, leading to a considerable decrease in the uncertainty of the existing estimates of the future runoff of the Ural River. Water management calculations for the Ural River were made with the use of the VOLPOW simulation model, which implements the solution of water balance equation by time intervals. The results of variations of the annual and seasonal runoff of the Ural River at different sections were obtained taking into account the effect of the Iriklinskaya Hydropower Station and the Sakmara River under scenarios RCP 4.5 and RCP 8.5 in the nearest future and in the late XXI century. The current potential of runoff regulation in the Ural River by reservoirs was evaluated, and variants of reservoir operation curves for the optimal use of the available water resources are presented. Variants are proposed for adaptation of the rules of runoff regulation by the Iriklinskoe Reservoir and its operation characteristics under expected climate changes in the XXI century, based on water management calculations with the use of long-term series of daily water inflow, determined by the ECOMAG model under scenarios RCP 4.5 and RCP 8.5 relative to the base period 1976–2005.

A numerical hydrodynamic model was constructed for the segment of the Ural River from the Iriklinskoe Reservoir (inclusive) to a site 30 km downstream of the Sakmara River inflow; therefore, the total length of the model reach was >700 km. To reduce the time of model development and to accelerate the calibration and variant calculations, the segment was divided into three successive parts of the channel, interacting through consistent boundary conditions. The simulation is carried out with the use of a domestic highaccuracy software package STREAM 2D CUDA, taking into account abrupt changes in bottom elevation and multifractional soil composition. The model was calibrated for constant water discharges. Calculations were carried out for a spring flood with an exceedance probability of 1% and a breakthrough wave of the Iriklinskii Hydropower System under two scenarios. Maximal water levels, depths, and inundation zones were obtained. An effect of a many-time increase in the steepness of the leading front of the flood wave within the domain was revealed.

The cartographic data on anthropogenically transformed areas within the Ural River basin were analyzed to reveal the features of their spatial heterogeneity. The characteristics of the distribution and longterm development dynamics of the main types of nature management, settlement system, transport infrastructure facilities, and large industrial plants were taken into account. The main factor of the spatial distribution of various types of economic activity was found to be the difference in the natural-resource potential due to the latitude-zonal and geological-geomorphological diversity of landscapes in the drainage area. It has been found that the most deeply transformed areas are located along the Ural River valley, which is due to the existing settlement system and the presence of guaranteed reserves of water resources. An important factor of the transformation of the Ural River drainage area is the mining industry, which forms large industrial agglomerations and serves as the main source of pollutants that enter river water.

Based on the analysis of the currently existing provisions applied in the management of water use in the river basins of the Russian Federation, taking into account the artificial regulation of river flow by reservoirs, it can be revealed that there are some flaws in them. For example, the guiding documents, including the “Methodological guidelines for the development of standards for permissible impacts on water bodies” the main characteristics of river basins that affect the conditions for the formation of river flow, the ecological and economic characteristics of the location and operation of reservoirs on small rivers, as well as indicators of the formation of additional water losses resources from their surface as a result of evaporation are not fully taken into account. This is primarily related to the basins of small rivers located in arid areas, which include the watercourses of the Ural River basin within its middle and lower parts. Taking into account the above, methodological provisions are proposed that, when designing and constructing reservoirs, provide for the need for a differentiated analysis of the physical and geographical conditions (geographical location, orography, water balance and other characteristics) of the territories where the basins of the studied rivers are located. This is of the greatest importance in the context of the formation of a regional response to global climate warming with the emergence of a set of adverse economic and environmental consequences.

The geosystem approach and the basin principle have been adopted as a methodological basis, which make it possible to comprehensively take into account the peculiarities of the influence of a combination of natural and anthropogenic factors on the formation of variability in quantitative and qualitative characteristics of watercourses and environmental conditions in them. The research methods include: physical and geographical zoning of the Ural River basin within the Russian Federation, statistical and graphical analysis of materials from long-term hydrometeorological observations, analogies, cartography, etc.

As a result of the conducted research, methodological provisions on optimal regulation of the flow of small rivers of the Ural River basin by reservoirs within the Russian Federation, taking into account ecological and economic criteria, are substantiated and proposed. They are part of an extensive list of proposals aimed at the hydrological and ecological restoration of small rivers, taking into account the need for various activities. In particular, the need to determine the optimal number and volume of small ponds and reservoirs in the basins of small rivers, taking into account their normal functioning in low-water conditions and ensuring regulatory water content in the lower links of the hydrographic network along the Ural River basin within the Russian Federation is of leading importance. Accordingly, these methodological provisions have been developed in order to maintain surface and groundwater in a condition that meets the requirements of the water legislation of the Russian Federation.

Transboundary transport of pollution by riverbed water flows creates environmental and economic losses in areas located downstream of rivers. At the same time, very serious problems arise not only on watercourses crossing state borders, but also on the borders between individual entities of the same country. First of all, the problem of reliability of water quality assessment arises, in conditions of significant instability of the hydrological regime, based on existing monitoring systems. This problem is considered using the example of a transboundary river. Ural. An algorithm for forming a constructive dialogue between interested parties is proposed by taking into account the statistical characteristics of the measurement results obtained at neighboring hydrochemical observation sites. The expediency of taking into account for this purpose the threshold of distinguishability of controlled indicators, assessment and regulation of errors of the 1st and 2nd types is shown. The possibility of establishing economic losses due to the lack of constructive relations between the parties in terms of assessing controlled indicators has been demonstrated.

Over the entire period of studies in the water bodies in the Ural River basin, comprehensive hyd-robiological studies have not been carried out in many areas both on the main watercourses of the Ural andSakmara rivers and on a large number of tributaries of different levels. The results of such studies carried outby the Water Problems Institute, Russian Academy of Sciences, during expeditions in the summer andautumn 2022 are discussed. A large body of data on phytoplankton, zooplankton, zoobenthos, and juvenilefish was collected and processed.