Using the ArcGIS and HEC-RAS software and the HEC-GeoRAS interface, I modelled floods with a 100-year return period on the Poljanska Sora river from the village Log nad Škofjo Loko to the confluence of the Poljanska Sora and Selška Sora rivers in Škofja Loka. On the basis of LIDAR data, I created the geometry of the river with compulsory data, such as stream centerline, bank lines, flow path centerlines, XS cutlines, and non-compulsory data, such as levees, ineffective flow areas, bridges, blocked obstructions and land use. With the latter, I extracted the roughness coefficients, i.e. Manning’s n Values. with the HEC-GeoRAS interface, I exported those data to HEC-RAS where I supplemented it with the geometry of bridges, which I got from the field measurements. I entered flow data and boundary conditions before running the model. The result of flood modelling shows the extent of the floods and the depth of the water. I displayed the result in the RAS Mapper and then exported it in ArcGIS where I displayed the layer of the modelled floods on an orthophoto. I classified the depth of the modelled floods in the classes as defined in the layers of flood risk areas. In the end, I compared those two layers and made the flood risk map.