Review of measures to increase the capacity of a stream culvert using 3D-CFD simulation

Mattias Deller, 12. November 2020

As part of the renovation of a culvert on the Rötelbach in the canton of Thurgau, measures to increase capacity were checked using a 2-phase (water/air) 3D-CFD simulation

Water level with flow velocities for the three examined stationary inflows

Stream culverts are hydraulically critical structures as the discharge capacities react sensitively to the condition of the bed, flow obstacles (e.g. pillars) and changes in the cross-section. In the analytical capacity assessment of stream culverts, these specific parameters cannot be taken into account, or only with great uncertainty. If the influence of these uncertainties is underestimated during planning or if incorrect assumptions are made, unexpected flooding and damage can be a result.

To minimize the mentioned uncertainties in the renovation project of a stream culvert on the Rötelbach in the canton of Thurgau, TK CONSULT AG was commissioned to validate measures for a capacity increase using a 2-phase (water/air) 3D-CFD simulation. As optimization measures, pillars in the culvert are removed and the inlet situation is improved by reducing inlet losses. The effect of these measures was checked using three stationary (HQ100, QDIM and HQ300) and one transient hydrograph. 3D-CFD simulations are a suitable and inexpensive tool that enables an enhanced understanding of hydraulic conditions. This allows optimization and planning measure effects to be determined in a targeted manner and the benefit of the investment to be maximized.

Simulation of the transient hydrograph, with a maximum inflow of 30 m3/s