Auckland Council required a full 2D flood study as a condition of resource consent before construction could proceed. The site was crossed by two overland flow paths draining from higher ground to the east and south-west. Council needed flood depths, velocities, pedestrian hazard mapping, and safe building levels confirmed at the 1-in-100-year event with climate change.
We built a 2D HEC-RAS flood model on a 1 m x 1 m grid using 2024 LINZ LiDAR terrain data. At this resolution the model picks up individual kerb lines, low points, and drainage features that control where water concentrates across the site.
The model identified two overland flow paths - one relatively minor, the other carrying nearly ten times the volume. Maximum flood depths reached 1.2 m in the lowest areas during the 1-in-100-year event. Pedestrian hazard zones were mapped where the combination of depth and velocity exceeded the safety threshold. Safe floor levels were set for every proposed lot above the modelled flood surface with freeboard.
The report confirmed that the proposed development layout would not obstruct either flow path, and included flood depth and velocity maps both with and without climate change applied.
A flood hazard assessment report that satisfied the Auckland Council consent condition. The report included the 2D model results, flood extent maps, pedestrian hazard mapping, and floor level recommendations for each lot. The consent proceeded to construction.
