My graduation thesis is about analysing hydraulic relationships of a reach of Ljubljana river and Gruberjev prekop. Chapter of flooding is presented. Then correlation with vegetation, which slows down the flow with it's structure and shape is overviewied. Influence of vegetation in reach Gruberjev prekop is highlighted, where among other things, trees are hanging in the river. Next chapter is about construction structures that interfere with the flow. These are bridges and bridge piers, weirs, ….Program Hec-Ras, which is used as analytical model of reach of Lljubljana river is introduced . At the end, we overlook results and interpret the correlation of flow between mestna Ljubljanica and Gruberjev prekop.