Method of Reconstructing Digital Elevation Model for Large-scale River Based on Copernicus DEM 30

[Objective] To address the challenges of incomplete remote sensing imagery and insufficient measured terrain data in large-scale river numerical simulations, this study proposes a novel method for river channel terrain reconstruction that integrates Copernicus DEM 30 data with limited measured data, aiming to solve the problem of constructing large-scale river channel DEMs in data-scarce areas and to verify its applicability in MIKE 21 hydrodynamic-sediment numerical simulations. [Methods] This study took the Alar-Xinquman river section of the Tarim River as the study area and utilized relevant hydrological data and measured terrain elevation data from 2011 as the basic dataset. The specific reconstruction process was as follows: (1) Using ArcGIS software, combined with Google Earth historical imagery and Copernicus DEM 30, the inner and outer bank lines of the river channel were delineated by scaling overlapping imagery proportionally to determine the main channel boundary.(2) The river DEM was corrected stepwise. First, the quadratic interpolation method was applied to densify the elevation data of the main channel cross-sections. Second, the mean difference method was used to calculate the deviations in elevation between measured points and the Copernicus DEM at corresponding locations, enabling an overall vertical correction of the Copernicus DEM data. Next, a locally weighted regression (LOESS) algorithm was introduced to correct the longitudinal cross-section elevations of the main channel, smoothing the riverbed terrain and generating the main channel DEM. Finally, the main channel and floodplain DEM data were merged to construct the complete river channel DEM.(3) The reconstructed DEM was imported into the MIKE 21 hydrodynamic-sediment module. Measured data such as water level, flow, and sediment concentration were selected as boundary conditions for numerical simulation. The accuracy and reliability of the reconstructed DEM were evaluated by comparing the errors between the simulated and measured values. [Results] Comparison between numerical simulation results and measured data revealed that the results for flow velocity, flow-stage relationships, and river channel erosion-deposition tests all met the allowable deviation requirements specified in relevant technical standards. This indicated that the river channel DEM constructed in this study was reasonably suitable for two-dimensional hydrodynamic-sediment numerical simulations. [Conclusion] (1) The river channel terrain reconstruction method proposed in this study, integrating Copernicus DEM 30, quadratic interpolation, mean difference method, and locally weighted regression (LOESS) algorithm, can effectively address the lack of measured underwater terrain data for large-scale rivers. It demonstrates superior continuity and accuracy compared to traditional single-interpolation methods.(2) The hydrodynamic model established based on the reconstructed DEM achieves simulation accuracy within the allowable deviation limits specified by relevant technical standards. This method is characterized by low cost, high efficiency, and strong applicability, providing a practical new approach and technical support for the numerical simulation of large-scale rivers with scarce data, such as the Tarim River.