Terrain Topography amd Debris-flow Modelling : Topografija površja in modeliranje gibanja drobirskih tokov

Debris flow hazard and risk assessment is not only based on assumptions on source areas and magnitudes of possible debris flows and their rheological characteristics, but also on their runout predictions. With regard to topographic presentation of slope surfaceover which a slope debris flow runs or presentation of a torrential channel along which a debris flow runs, this paper reports on the results of two-dimensional modelling of possible debris flows on selected torrential fans in the Sava Dolinka valley as a function of the numerical square grid (5 x 5 m, and 15 x 15 m), generated from freely available digital elevation model DEM 5. From the aspect of debris-flow numerical modelling we showed that buildings that are not shown on DEMs should be modelled, because they have largeinfluence on the flow field close to them. The approach to introduce buildings into the numerical grid model by simply defining them as blocked (dry) cells proved to be better solution than raising the roughness coefficient in these cells to account for flow obstructionby buildings. We also checked the applicability of the digital elevation model DEM 12.5 and generated from it a numerical grid 12.5 x 12.5 m. In the case of the Trebiža torrential fan it can be concluded that DEM 12.5 can be more geomorphologically representativethan DEM 5. The next step in modelling natural hazards such as debris flows will eventually be the application of even more precise numerical grid, generated from LIDAR surveys of relief