CFD Modelling of Stormwater Overland Flow at the Entrance to a Road Underpass

The Buckle Street underpass is part of the Memorial Park project being delivered by the Memorial Park Alliance. Investigations of stormwater systems for the proposed Buckle Street underpass indicated that overland flows posed a flood risk to the underpass. Star CCM+ Computational Fluid Dynamics (CFD) software was used to model the stormwater flow through the intersection. The flow of water entering and bypassing the underpass was quantified.

The site is located at the intersection of Taranaki, Buckle and Arthur Streets, Wellington. The Taranaki Street catchment above the intersection is 23.3 ha and relatively steep with a high proportion of impervious surfaces. The overland flows entering the intersection were predicted to be 5.4 m3 /s. Some of the overland flow from Taranaki Street will be diverted down the underpass. The design of the intersection and underpass drainage has been designed to accommodate these overland flows.

CFD modelling was undertaken to refine the intersection surface design, to assist in striking the best balance between a safe road alignment and flood protection. The exact nature of CFD modelling allows the evaluation of the effect of small changes in camber on the volume of water entering the underpass. The results from this study show an encouraging progression in the application of CFD to complex overland flow applications in engineering.