Problems, methods and technologies of combined 3D model construction for underwater and above-water relief

In the article we describe the methods for construction of underwater 3D relief (bathymetry) and combining it with the corresponding ground relief (terrain) when the bathymetry information is of much lower quality than that of terrain. We have developed an algorithm for combining the low quality underwater relief with the higher quality ground relief using Delaunay triangulations. The resulting combined 3D model of relief has no noticeable artifacts and can be used to solve various hydrological tasks, such as computation of the HPP reservoir water level in dependence to the water discharges of the hydroelectric power plant. We have tested the technology for building combined relief 3D model in several scientific projects intended to estimate the changes in the coastline under various water flow scenarios in the basins of Angara River and Lake Baikal.