CHRISTCHURCH CITY MEGA MODEL - MAGIC OR MADNESS?

The Canterbury earthquake sequence resulted in significant changes to the land drainage network in Christchurch. In order to better understand the impacts of the earthquakes on flooding the Christchurch City Council (CCC) undertook an ambitious three-way coupled hydraulic modelling project across almost all of ‘flat-land’ Christchurch. This will be used by the Land Drainage Recovery Programme (LDRP) to support identification and prioritisation of repair and remediation options. It will also be a powerful tool for CCC to use to investigate resiliency of the city against climate change and sea level rise effects.

The goal of the modelling was to establish earthquake effects and to develop a tool to inform options assessments. The level of detail required to accurately quantify the effects and to support investigations required modelling of the road corridors, 304 km of waterways and 554 km of pipes down to 300 mm diameter across an area of 17,195 ha. The high level of detail was required to capture the full extent of the earthquake changes, for example, settlement in areas remote from the main river channels. These project requirements have led to innovative modelling approaches.

This paper briefly explains the scale of the problem, solution definition, model development and some of the early findings of the modelling. Some of the challenges that were overcome include; building a high resolution surface model following a significant change to the land surface, deciding how a pre-earthquake model should be defined, building a large complex model that runs quickly, dealing with inter-catchment flows in very flat topography, addressing data gaps, and meeting tight programme deadlines. The paper also explains the benefits and detriments of the approach and how an open dialogue between the Council and the Consultant led to a robust and powerful tool.