ABSTRACT Flooding is one of the costliest natural hazards in Aotearoa New Zealand. To enable consistent nationwide flood modelling, necessary for comparing hazards and risks between regions and for collating results at a national scale, hydrologically conditioned Digital Elevation Models (DEMs) and hydraulic roughness maps are essential. While Aotearoa New Zealand has widespread LiDAR coverage, there is no national integrated land and sea hydrologically conditioned DEM or hydraulic roughness maps suitable for flood modelling. We have produced a nationally consistent 8m hydrologically conditioned DEM and hydraulic roughness product using the latest data available, in April 2025, across the three main islands of New Zealand (North, South and Rakiura Islands) to a minimum distance of 20 km offshore. Land elevations are primarily derived from LiDAR surveys, while offshore and coastal elevations including 97 estuaries and rivers are primarily derived from a curated elevation dataset developed for tidal modelling with spatial resolution down to 5 m in estuaries to 15 km offshore. The dataset also incorporates measured bed elevations for 58 lakes and the estimated bed elevations for a further 99 rivers and river mouths. Finally, culverts and waterways (as defined on OpenStreetMap) were daylighted (obstructions removed and opened to the sky), while the crest elevation from 5284 km of stopbanks was preserved. This product is freely accessible in a Zenodo dataset 10.5281/zenodo.16734446 . This dataset is generally applicable for use in compound flooding, coastal hazard, coastal impacts of tectonic deformation, landslide modelling, catchment and river network generation, and fish passage modelling.
Pearson et al. (2026) studied this question.