What this measures
For every block, Lotline takes its lowest ground from LINZ’s elevation data (LiDAR where it exists, otherwise the national 8 m model) and compares it with the level of the nearest mapped river within 1 km. The river’s level is the lowest ground along it within 100 m of the point nearest the block. Small streams are left out: on almost every block there is a drain or creek at its own level, and that says nothing about a river flooding.
It is a measurement, not a flood map. It doesn’t see stopbanks, rain falling on the block, water running off the hills, the coast, or streams too small to be mapped. A council flood map, where there is one, is the authority.
| Lowest ground on the block | Blocks | Share | |
|---|---|---|---|
| Up to 3 m lower than the river at its nearest point | 44,530 | 11.0% | Often floodplain, or land behind a stopbank. |
| Within 2 m above it | 32,858 | 8.1% | Low land close to a river. |
| 2 to 10 m above it | 47,692 | 11.8% | |
| More than 10 m above it | 45,467 | 11.2% | |
| Falls away well below the river point (more than 3 m) | 14,824 | 3.7% | Usually a block running down a valley away from the river: no single height is meaningful. |
| No river of this size within 1 km | 218,790 | 54.1% | Smaller streams and water off the land can still flood. |
Does it say anything about flooding?
We checked it against the one flood we hold a mapped extent for: Cyclone Gabrielle, February 2023 in Hawke's Bay, which the regional council mapped from what actually flooded. Of the 14,242 blocks inside that map’s area, 2,025 (14%) had a quarter or more of their land flooded.
| Lowest ground on the block | Blocks | Flooded in 2023 |
|---|---|---|
| Within 2 m of the river’s level, or up to 3 m lower | 3,007 | 41% |
| 2 to 10 m above it | 1,973 | 18% |
| More than 10 m above it | 1,992 | 4 of 1,992 |
| Falls away well below the river point | 597 | 9% |
| No river of this size within 1 km | 6,673 | 6% |
Low land close to a river flooded far more often than the region as a whole, and land well above its river almost never did. Blocks that fall away well below the river point they were compared with flooded less often than average, which is why the report gives them no height. Blocks with no river of this size nearby still flooded too, from smaller streams and water off the land. This is one region and one extreme event: it shows the measurement points the right way, not how likely any one block is to flood.
By region
| Region | Blocks | Within 2 m of the river’s level, or up to 3 m lower | No river of this size within 1 km |
|---|---|---|---|
| Canterbury | 51,188 | 28.4% | 50.8% |
| Southland | 21,847 | 25.6% | 48.7% |
| Marlborough | 8,921 | 24.9% | 51.4% |
| West Coast | 10,314 | 24.8% | 42.4% |
| Hawke’s Bay | 18,180 | 24.6% | 41.5% |
| Tasman | 11,077 | 22.0% | 46.6% |
| Gisborne | 7,801 | 21.8% | 38.9% |
| Wellington | 18,953 | 21.7% | 45.9% |
| Otago | 29,457 | 21.3% | 46.7% |
| Manawatū-Whanganui | 39,866 | 19.8% | 45.7% |
| Waikato | 58,496 | 18.1% | 52.6% |
| Bay of Plenty | 23,524 | 16.8% | 59.2% |
| Northland | 46,126 | 13.6% | 67.1% |
| Taranaki | 18,348 | 12.3% | 57.3% |
| Nelson | 1,052 | 11.4% | 63.6% |
| Auckland | 39,010 | 6.1% | 76.8% |
What to check
- Look the block up. The full report gives its lowest ground against the nearest river, and the council flood maps Lotline holds for its district.
- Get the council’s LIM. It records the flood hazards the council knows about, and whether a stopbank protects the block.
- Earth Sciences NZ’s national flood map shows where a 1-in-100-year rainstorm is modelled to flood, across 256 floodplains. It is free to view; its licence allows non-commercial use only, so Lotline links to it rather than including it.
- Ask neighbours how high past floods came. Nothing in the records knows that better.
Lowest ground: LINZ elevation (CC BY 4.0). Rivers: MfE River Environment Classification, reaches of Strahler order 4 or larger (CC BY 4.0). Flood extent: Hawke’s Bay Regional Council’s mapped 2023 flood (CC BY 4.0). Heights are to the nearest 0.5 m.