The article describes the methodology for constructing digital elevation models for the vast delta areas of the Don and Volga rivers for further use in mathematical models of flooding from surges. The initial cartographic data and features of the delta regions are described. The methods of information processing are considered in detail. An algorithm for constructing a DEM has been developed to obtain highly detailed digital elevation models. The algorithm is based on combining the DEM of individual key features - land, the depths of the hydrographic network and the bathymetry of the receiving reservoir for the river. The topographic maps, maps of the navigable route depths, hydrographic maps, and satellite images Landsat-8 and Sentinel-2 were used to create the DEM of the Don and Volga river. To build individual DEMs, a raster of the absolute depth of the channels, a hydrography DEM, a land DEM, and a shelf DEM were created using geoinformation systems. To assess the possibility of using obtained DEMs in hydrological models based on HEC-RAS, we conducted training and verification calculations of water level during wind surge phenomena in Don Delta using different surface roughness coefficients. The calculation results show good reproducibility of observed water level fluctuation in the Don Delta using obtained DEM with a roughness coefficient of 0.0125. Also, we carried out similar calculations of storm surge phenomena in the Volga Delta using obtained DEM and combinations of various riverbed and not riverbed roughness coefficients. The combination of 0.007 for riverbed and 0.02 for not riverbed surfaces reproduces the observed water level fluctuation during storm surge phenomena in Volga Delta. The constructed DEMs for the Volga and Don deltas made it possible to reproduce the observed dynamics of river discharges and water level fluctuations during surge events. Such detailed DEMs, taking into account all the complexity of the coastal and delta relief, were created for the first time for the Volga and Don.