Accuracy and Uncertainty Assessment of Spatial Interpolation Methods for Reservoir Bathymetric Modelling

Abstract

Accurate estimates of reservoir storage and long-term capacity loss are essential for reliable operation, sediment-management planning, and risk-informed decision making. However, bathymetric point surveys are irregularly distributed, and the reconstruction of the submerged surface introduces interpolation uncertainty that propagates into stage–storage curves and capacity-loss estimates. This study investigates the influence of spatial interpolation uncertainty on reservoir capacity-loss estimates and evaluates long-term sedimentation by comparing reservoir-bed conditions in 1987 and 2023 using Kamashi Reservoir (Uzbekistan) as a case study. Historical reservoir-bed conditions were reconstructed from digitized and georeferenced engineering topographic maps prepared in 1987, while the 2023 reservoir bed was modelled using bathymetric survey data. Five surface modelling approaches Inverse Distance Weighting (IDW), Radial Basis Functions (RBF), Ordinary Kriging (OK), Universal Kriging (UK), and Empirical Bayesian Kriging (EBK) were calibrated under a unified grid, extent, and neighbourhood design and assessed using leave-one-out cross-validation (LOOCV). Uncertainty was propagated via residual-bootstrap Monte Carlo simulation (10,000 realizations per method), and differences among methods were tested using ANOVA and Tukey’s HSD (p < 0.001). EBK provided the most robust performance (RMSE = 0.569 m; R² = 0.9806), while OK minimized MAE (0.32 m); both showed near-zero bias. Comparison of the reconstructed reservoir-bed surfaces from 1987 and 2023 revealed substantial sediment accumulation and morphological changes within the reservoir basin. Updated elevation–volume relationships derived from the reliability-ranked EBK model indicate a total capacity loss of approximately 7.7 Mm³ (30.8%) since 1987 and near-complete infilling of dead storage (~97.5%). DEM-of-Difference (DoD) analysis revealed spatially heterogeneous sedimentation, with deposition reaching +8.26 m and localized erosion of up to −1.20 m. The proposed workflow provides practical quality control for bathymetric modelling and supports reliable assessment of reservoir sedimentation and capacity loss. The results can assist operational reservoir management and provide a scientific basis for planning sediment-removal and dredging activities.