Hydrodynamically Coupled Stormwater Model of the Auckland Central Business District

The Auckland C entral Business District (CBD) has been experiencing flooding problems, particularly in the downtown area close to Waitemata H arbour. It was thought that these problems were being caused by a number of factors; including, insufficient inletting capacity, insufficient network capacity and backwater effects. A stormwater network model was considered necessary to understand the response of the catchment and its existing network to rainfall, to identify areas potentially at risk of flooding and to identify the critical factors contributing to the flooding.

A hydrodynamically coupled one-dimensional (1D) and two-di mensional (2D) model of the CBD was developed for this purpose. Due to the complexity of the CBD catchment, a unique model setup was required to ens ure all flow regimes were represented accurately. AECOM collaborated with DHI New Zealand to conceptualise an innovative methodology that incorporated catchpit modelling and a combination of hydrological methods using MIKE 21 “rain-on-grid” approach, MIKE 21 source points and MIKE URBAN catchment loading.

This paper outlines the methodology for the detailed stormwater modelling of the Auckland CBD. This complex modelling approach posed a few interesting technical challenges that are also discussed including the relevant solutions found and the lessons learnt.