Investigation of the influence of bank re-formations on the actual usable capacity of the Tasutkol reservoir

In southern Kazakhstan, the increasing demand for water necessitates a reassessment of ageing reservoir capacities affected by siltation and shoreline changes. This study quantified the usable capacity of the Tasutkol Reservoir (commissioned in 1974) through long-term field observations, shoreline analyses, hydrometric measurements, and bathymetric controls from 2008 and 2020. Wave regime data from the Baytyk and Shu stations were used to calculate design wave heights and storm powers. Sedimentation mechanisms were analyzed, revealing that bank reworking contributes 29–32% of total siltation, while fine suspended material bypasses the reservoir, flowing downstream. The reservoir’s useful capacity decreased from 342 to 263.1 million m3, with a net loss of 8.3 million m3 from bank-derived material, despite a 4.9 million m3 gain from shoreline retreat. The approach’s accuracy was supported by a 7–9% agreement between calculated and bathymetric estimates. Projections suggest that by 2030, useful storage could decline to 200 million m3, with sediments occupying 80–90% of the volume by 2040. These results highlight the importance of regular bathymetric monitoring and targeted bank-protection measures to ensure ongoing irrigation and operational safety.