The use of hydraulic models for carrying out flood simulations is a common practice globally. The current study used HEC-RAS (2D) in order to simulate different flood scenarios on the River Yesil (Ishim). Comparison of different mesh sizes (25, 50 and 75 m) indicated no significant difference in model performance. However, a significant difference was observed in simulation time. In addition, the inclusion of breaklines showed that there was a slight improvement in model performance and a shortening of the simulation time. Sensitivity analysis and the consequent manual calibration of sensitive parameters resulted in a slight improvement (an increase in the model accuracy from 58.4% for uncalibrated to 59.7% for calibrated). Following the simulations inundation maps for 10-, 20- and 100-year flood events were obtained. Hazard classification of the flood extents generated indicated that the settlements of Zhibek Zholy and Arnasay were flooded in all the simulated events. Volgodonovka village experienced flooding when a 100-year flood event was simulated. On the other hand, settlement No. 42 did not experience any flooding in any of the scenarios. The model results also demonstrate that the Counter-Regulator was not overtopped in the event of the 100-year hydrograph.

Flooding events have been negatively affecting the Republic of Kazakhstan, with higher occurrence in flat parts of the country during spring snowmelt in snow-fed rivers. The current project aims to assess the flood hazard reduction capacity of Alva irrigation system, which is located in the interfluve area of Yesil and Nura Rivers. The assessment is performed by simulating spring floods using HEC-RAS 2D and controlling the gates of the existing system. A digital elevation model of the study domain was generated by integration of Sentinel-1 radar images with the data obtained from bathymetrical survey and aerial photography. Comparison of the simulated inundation area with a remote sensing image of spring flood in April 2019 indicated that the main reason for differences was due to local snowmelt in the study domain. Exclusion of areas flooded by local snowmelt, which were identified using the updated DEM, from comparison increased the model similarity to 70%. Further simulations of different exceedance probability hydrographs enabled classification of the study area according to maximum flood depth and flood duration. Theoretical changes on the dam crest as well as additional gates were proposed to improve the system capacity by flooding agriculturally important areas, which were not flooded during the simulation of the current system. The developed model could be used by local authorities for further development of flood mitigation measures and assessment of different development plans of the irrigation system.

Introduction. The article analyzes water security issues in river basins of the Kazakhstan-Russia border region, as well as transboundary cooperation in this area. These issues are analyzed from a Kazakhstani perspective, which has distinct characteristics compared to the Russian perspective but cannot be considered without taking the latter into account. Methods and materials. The study is based on the concept of water security. For the first time, the northern water basins of Kazakhstan with their transboundary rivers are viewed through the lens of this concept as a single entity with common problems, many of which require solutions at the international level. The study also relies on an analysis of the strengths and weaknesses of Kazakhstan-Russia agreements on transboundary river issues, as well as a quantitative analysis of water levels, pollution, and other characteristics of the relevant water basins. Data obtained from Kazakhstani state institutions, particularly from the state enterprise “Kazhydromet,” are analyzed. Using this data and the ArcGIS program, maps of Kazakhstan’s hydrographic basins were compiled. Analysis. The key security issues of the northern Kazakhstani transboundary water basins, including water scarcity, floods, pollution, and the degradation of biodiversity in coastal areas, are examined. Additionally, the effectiveness of Kazakhstan-Russia cross-border cooperation in addressing these issues is evaluated. Results. In the long term, water scarcity is the most serious challenge to water security, but natural disasters also require serious attention and more effective transboundary cooperation. It would be unjustified to place the primary responsibility on either single side for the water security issues in the region, as both countries have similar infrastructure and inherited economic development priorities from the Soviet era. The effectiveness of Kazakhstan-Russia cooperation in addressing water security issues remains ambiguous: on the one hand, the parties strive to resolve existing problems constructively, but on the other hand, their willingness to undertake coordinated and costly steps is quite limited. Contributions. K. Abdrakhmanov conducted SWOT analysis of empirical issues related to transboundary rivers and (together with S. Golunov) issues of transboundary cooperation between Kazakhstan and Russia; S. Golunov conceptualized the problem of water security, applied it to the empirical parts of the work, and analyzed the issues of floods and threats to biodiversity; M. Muzdybayev collected and analyzed data on hydrography, hydrology, water use, and the environmental state of Kazakhstan’s water basins; Ye. Karakulov and A. Kabdeshev categorized and compiled cartographic material for the hydrographic basins of Kazakhstan using the ArcGIS program.