Assessing sediment-induced storage capacity loss in the Hisorak Reservoir, Uzbekistan

• Ordinary Kriging (OK) showed the highest accuracy for geostatistical sedimentation analysis. • Sedimentation exceeded projections, with a 23.2 % storage capacity loss over 42 years. • Sediment rate 2003–2022 was 0.88 Mm 3 yr −1 , three times higher than design. • A 40 m thick sediment layer has accumulated near the dam site. • Surface Difference Map (1980–2022) revealed upstream sedimentation and downstream erosion. This study examines the long-term sedimentation dynamics and their impact on the storage capacity of the Hisorak Reservoir over 42 years (1980–2022). Sedimentation rates, capacity loss, and spatial volume changes were analyzed by comparing the original design data with bathymetric surveys conducted in 2003 and 2022. Four interpolation techniques—Inverse Distance Weighting (IDW), Radial Basis Function (RBF), Ordinary Kriging (OK), and Empirical Bayesian Kriging (EBK)—were applied to process bathymetric data and evaluated using RMSE, MAE, R 2 , and SDpred. Among them, OK provided the highest accuracy (RMSE = 1.13, MAE = 0.008, R 2 = 0.996). The resulting spatial model enabled precise capacity calculations, showing a reduction of 39.4 Mm 3 (23.2 %) in reservoir storage due to sedimentation. Between 2003 and 2022, sediment accumulated at an average rate of 0.88 Mm 3 yr −1 , more than three times the design estimate of 0.272 Mm 3 yr −1 . A Surface Difference Map revealed concentrated deposition in upstream zones and erosion along reservoir boundaries. These findings demonstrate that sedimentation is progressing faster than anticipated, causing accelerated storage loss. The study highlights the usefulness of geostatistical methods and surface difference analysis for assessing reservoir sedimentation and supports the development of more effective management and sediment-control strategies in arid-region reservoirs such as Hisorak