Cardno Pty Ltd and Scentre Group
Managing Flooding of Warringah Mall in Brookvale

Warringah Mall is a regional shopping centre located within the Brookvale Creek catchment in the Sydney’s northern suburbs. Studies in 2006, 2007 and 2008 identified that under existing conditions Warringah Mall is flooded by overland flows and overflows from Brookvale Creek. 1D/2D modelling approaches were adopted to assess existing flooding problems and structural options including a major drainage augmentation through Warringah Mall.

A major stormwater augmentation scheme within the Warringah Mall site was developed, assessed and approved with conditions by Warringah Council. One of the conditions of consent required a physical model study of the two large junction boxes, to confirm the hydraulic losses which were assumed in the computer model studies and to provide advice on how the hydraulic losses in each junction box can be minimised.

A comparison of the predicted and observed hydraulic losses and flood levels concluded that the current numerical 1D/2D model results appear to be conservative in comparison with the physical model results (which may be due to differences in adopted conduit roughness values in the numerical model and the roughness of the conduits in the physical model) and that the flood levels estimated by the numerical model are likely to be conservative.

Photos below show one of the modelled culvert configurations during testing and the first stage of culvert construction.