Waikawa Bay Culvert Repair Project

The SH35 Waikawa Culvert repair project was designed to address critical damage caused to a section of rural state highway by a severe storm event in December 2021. The storm triggered a debris flow that destabilized the road embankment and damaged the culverts, resulting in the temporary closure of the highway. McCaffrey and Cable Consultants (MaCC) undertook Geotechnical site assessment and civil engineering design of a new culvert on behalf of the New Zealand Transport Agency (NZTA), aimed to restore safe passage along the coastal SH35 route while ensuring resilience against future erosion and storm impacts.

MaCC’s engineering team conducted geotechnical assessment to determine the necessary steps for stabilizing the embankment and preventing further slope failure. The repair plan included installing a gabion retaining wall for slope stability, reinforcing the embankment with geotextiles, and upgrading the existing culverts to 1.2m HDPE pipes for improved stormwater management. These features were chosen not only to restore the previous infrastructure but also to enhance its long-term durability, with materials selected to align with environmental guidelines for coastal highway repair.

To accommodate local wildlife, the design incorporated provisions for fish passage, an essential component of sustainable infrastructure in New Zealand’s coastal environments. MaCC also employed erosion control measures, including a rock-filled embankment and riprap, to manage water flow and protect against further erosion. This culvert repair project demonstrates MaCC’s commitment to sustainable and resilient coastal highway infrastructure solutions.