Efficient Modelling of Complex Catchments in East Christchurch

The eastern Christchurch catchments of New Brighton, Bridge Street and Southshore total approximately 600ha. Understanding and managing these stormwater catchments is complex with low lying areas, tidal boundaries, and relatively flat grades. This complexity has increased following the Canterbury earthquakes.

To assess levels of service and compare options for managing stormwater in these catchments, SCIRT engaged Beca to carry out coupled 1D and 2D modelling using MIKE FLOOD software.

The models evolved through the design stages, from concept to detailed design of pipework, roads, storage and pump stations, including assessment of pre- and postearthquake change and performance against various level of service options. To meet project timeframes a number of measures were adopted.

The model build was streamlined, with pipe and surface data exported from SCIRT’s 12d design software and imported into the models. The number of model runs, particularly 2D model runs, was restricted. Manual calculations were used initially, then storm and tide combinations were tested using a modified 1D model, before a final 2D model was run. The size of the 2D grid was also optimized to achieve sufficient resolution without excessive run-times.

This approach meant that the modelling provided the required design inputs within tight timeframes.