Designed to protect Kaikoura from flooding, the Lyell Creek floodwall utilises the durability and versatility of concrete to create a piece of town infrastructure that is both effective and aesthetically pleasing.

Kaikoura has been flooded 16 times since 1923, including the devastating Christmas Eve flood of 1993 that caused $12 million in damage and prompted a review of the town’s flood protection. After careful assessment of available reinstatement options, it was decided to provide a channel with the capacity to convey all the floodwater that could flow under the SH1 bridge to the sea.

case study 8_photo2.jpgThe challenge was to provide a flood channel through the backyards of shops and the most frequently used tourist area in the township. Given the very limited space available, and the requirement for increased flood capacity, a new continuous protective concrete wall was selected as the only practical solution to address flooding issues. Construction began in 2004 and was completed two years later. The project is the culmination of 10 years’ work by Environment Canterbury to provide better flood protection further upstream.

The 400m-long wall has been designed to keep floodwaters out of the town. While the floodwall can contain a 160m3 per second flood, the foundations were designed to allow the height of the floodwall to be increased to match any future growth in flood capacity that could result if the state highway bridge was raised.

The floodwall has numerous innovative features, such as a section with an adjustable weir installed, which will allow fine-tuning during floods to maximize flood capacity. Removable stop logs have also been incorporated to allow town floodwater back into Lyell Creek in the event that water gets into the town upstream at the state highway bridge.

Where possible, the position of the wall has been adjusted to improve car parking and access to buildings. A wavy wall top was incorporated into the precast concrete panels, which along with an exposed concrete aggregate surface decoration enhances the visual appeal and evokes the nearby seascape.

With co-operation from Kaikoura District Council, the finished work also incorporates a concrete amphitheatre and a new concrete footbridge to the beachfront, which are well used by locals and tourists alike. Inviting the locals to choose the wording that would be cast into the concrete contributed to community ownership of the project. After consideration, the local runanga suggestion was adopted: “KI UTA KI TAI - The Conservation and Protection of the Mountains to the Sea”.

Extensive consultation during the project revealed opportunities for associated community enhancements. The result is an innovative, flexible, cost-effective and aesthetically acceptable piece of infrastructure that relies heavily upon concrete to not only mitigate flooding, but also to foster civic beautification and social inclusion.