Regional Flood Estimation Tool for NZ


To provide up to date flood magnitude estimations for New Zealand catchments to inform the  decision making and design of built infrastructure.


This tool represents a new model of flood magnitude for New Zealand catchments, and a re-assessment of the uncertainty inherent in the existing method that this work is intended to replace.

The previous method for flood estimation, dating from 1989, needed updating because more extreme events have been observed in the interim, and because of the probable effect of climate change, which will increase into the future.

The new dataset has twice as many sites, and three times the annual maxima than the previous study. The uncertainty of the previous model for estimating mean annual flood is larger than originally stated. This is confirmed by testing the current dataset tested against the earlier method.


Flood Estm1

Maps of catchments included in 1989 modelling (left) and current 2016 modelling (right)


The derivation of a new model for mean annual flood has proved more difficult than expected, at least to the extent that the eventual uncertainty is more than twice the previously published estimate of ~±22%.

The initial intention for redevelopment of this tool was to provided a web-tool to provide access to the new estimations. However due to the current performance of the new model this has not been finalised. The proposed next step for this tool is follow-up consultation with regional council stakeholders to determine future actions for refinement and delivery.

State of Development Unknown

Development Contact


Outcome Areas Environmental
Management Domains Natural Hazards
Intended End Users
  • Regional Council Scientist
Steady State or Dynamic Unknown

Input & Output Data


Open/Closed Source Closed Source

User Information

Operating Systems MS Windows, Mac OS X
User Interface Please Select
Ease of Use Please Select

Technical Considerations

Analytical Techniques Input/output
Keywords Flood estimates, Hazards, infrastructure

Tools for estimating the effects of climate change on flood flow: A guidance manual for local government in New Zealand - Ministry for the Environment online report

Key References

Henderson, R. and Collins, D. (2016): Regional Flood Estimation Tool for New Zealand - Final Report. Prepared for EnviroLink Tools (MBIE) August 2016, NIWA Client Report No: 2016049CH