CFD Kroisbach - Detailed hydraulic assessment of the maximum flow capacity in the covered Kroisbach incl. subsequent Grazbach

According to an available model assessment, a flood discharge of the Kroisbach can no longer be completely drained from a statistical return period of about 100 years (HQ100) in the covered area of the Kroisbach in the park of the Graz University of Music. The flooding potentially resulting from an HQ100 would presumably endanger the area between the inlet of the Kroisbach in the park of the University of Music and the main square of the city of Graz. For this reason a) the inlet area of the Kroisbach stream is modelled in detail in the covered stream cross-section, b) the hydraulic capacity from the confluence of the Kroisbach with the Leonhardbach (from this point on referred to as Grazbach) is checked in the following Grazbach, and c) a possible hydraulic influence of the confluence on the performance of the inlet area of the Kroisbach stream is assessed. The objectives of the project are a) to be able to estimate as accurately as possible the actual hydraulic discharge capacity in the covered Kroisbach and then further in the following Grazbach and b) on this basis to have the basis for possible structural adaptation options in order to increase the pumping capacity in this covered stream section in the inflow area (e.g. by removing a wall on the left bank, which currently narrows the free cross-section at the beginning of the covered stream section of the Kroisbach). For the detailed hydraulic assessment of the inlet area and the hydraulic impact of the confluence of the Kroisbach and Leonhardbach rivers, high-resolution 3D CFD models are required for these two locations. These 3D CFD models are flanked by 1D or 2D hydrodynamic models in the boundary and transition areas. To support and validate the 3D simulation results, hydraulic model tests must be carried out on a suitable scale.