A numerical investigation of a hydropower tunnel has been implemented in this project. The tunnel geometry data were taken from a laser scanning of a tunnel positioned in Gävunda, Sweden. While the average cross-section of the tunnel is even, in accordance with the pre-excavation schematics, the instantaneous deviations are significant. ANSYS-CFX was applied for the simulations using a RANS approach with k-ε model for turbulence closure. To evaluate the results, the pressure was area averaged in 30 planes evenly spaced perpendicular to the flow direction inside the tunnel. Additionally, the pressure was sampled along a line running from the inlet to the outlet of the tunnel. Results show that the area averaged pressure is similar to the pressure modelled along the center line. This means that the roughness has a dominating effect on the bulk flow inside of the tunnel. Hence, cross-sectional based methods of evaluation (e.g. Gauckler-Manning) could potentially be used to evaluate the localized pressure inside the tunnel. Further evaluation show that the Gauckler-Manning and Haaland equation both can be used as an estimate of the modelled pressure inside of the tunnel. Both equations are highly dependent on the hydraulic radius and cross-sectional area. These results have many implications, continuous pressure measurements can potentially be used to monitor the structural integrity of tunnels. Similarly, tunnel data could be used to estimate pressure effects within the tunnel, which would enable easier and reliable risk assessment studies.