Dynamic Coupled Modelling of Oakley Catchment - Auckland New Zealand

The Oakley Catchment (1230 Ha), centred around Oakley Creek, is a long narrow stormwater catchment on the Auckland Isthmus. The stormwater response to extreme events creates flooding across a broad floodplain adjacent to the creek. State Highway 20, Stage 1 was completed in 2007/08 and is now programmed for extension to Waterview. The highway will run alongside Oakley Creek, therefore the predicted flooding will influence the design of the motorway and portals for the tunnel section.

Previous models developed to represent flooding in the catchment provided low confidence results. Flooding in Oakley results in complex flow regimes including a wide range of velocity profiles and flow directions in the creek and surrounding floodplains. Recent advancements in modelling software allowed for complete dynamic modelling of flows by coupling the creek, pipe network (1D model) and floodplains (2D model) into one complete, higher confidence, dynamic model.

This paper outlines the improvements made and the lessons learned whilst developing this model. The paper concludes that a coupled model is a valuable tool for flood risk assessment and input to the motorway design and flooding solutions. It was identified that a 1D, and even a 2D model alone, is not appropriate for representing Oakley catchment hydraulics.