Managing Post-Earthquake Stormwater Risk in New Brighton

The Christchurch suburb of New Brighton is bounded by the Pacific Ocean to the east and the Avon River/Ōtakaro and Avon-Heathcote Estuary/Ihutai to the west. It drains towards the lower Avon River and the Estuary, both tidally influenced. During the Canterbury earthquakes, the area suffered from liquefaction, land settlement (up to 600mm) and lateral spreading. Some areas are now very low-lying relative to extreme high tides. This creates significant challenges to restoring the stormwater drainage performance.

This case study of the Bridge Street catchment in South New Brighton explores the challenges in servicing the area and managing stormwater runoff and flood risk. These challenges include draining low-lying land during high tide events, difficult ground conditions, high and tidally influenced groundwater, and heightened seismic risk, as well as maximising reuse of existing infrastructure. Solutions include reconfiguring the catchment outlets, providing a new stormwater basin to contain stormwater during high tide events and a pump station for large events, plus careful material selection and detailing to provide a more resilient system.

The design involved a multi-disciplinary team of civil, geotechnical and structural engineers working together with modellers, landscape architects and Council stormwater staff and parks planners. The works are currently under construction.