Olga Kovalova, University of Latvia Abstract – In order to set up a "hydrologically accurate" digital model of landscape, which allows identifying borders of flooded territories in the period of changes in the water level, it is important to have data in the hydrography stratum on the direction of river streams. The given issue can be solved by creating a geometrical network of sustainable water streams. The geometrical network of sustainable streams represents a mathematic model of different network structures object classes