National rainfall and runoff guidelines - We'd like you to get involved

For several years, the IPENZ/Water NZ Rivers Group, the Water NZ Modelling and Stormwater Special Interest Groups, as well as a number of other individuals have been pursuing the development of national rainfall and runoff guidelines for New Zealand. These would be analogous to guidelines found in other countries, including the well-known Australian Rainfall and Runoff (ARR) guidelines, which have recently been updated.

There is widespread support within the sector for this work. The guidelines would support improved decision-making (and therefore cost efficiencies) on matters such as natural hazard risk assessment and infrastructure investment including flood protection schemes, stormwater systems, and the design of structures such as bridges and culverts. The work is also critical to understanding water quality pressures more accurately so that costly mitigation options can be robustly assessed.

In NZ, geographically specific methods of undertaking hydrological analyses have been developed in bigger centres (for example, TP108 in Auckland). These are frequently used outside the regions where they were developed, often inappropriately. In addition, where methods do exist for an area, they can be applied inconsistently giving different results from the same input data. The scale of error can be as high as +/- 50-100% which presents a high risk of poor or sub-optimal investment decisions. Communities are bearing the cost of these decisions through higher rates and housing costs, or through physical damage as a result of infrastructure failures (e.g. flooding).

Progress to date and next steps

In 2015-16 funding was sought from the Treasury’s better business case seed fund. Unfortunately the bid was rejected. The significant scale of the project is a particular challenge to securing funding.

Work plan and priorities

We are now looking to break the work into more manageable chunks and prioritise effort on some priority sub-projects.

To that end, we are conducting a two-stage gap analysis as follows:

  1. Initial screening survey about priorities (in progress) – click here to download the survey.
  2. More detailed gap analysis of specific topic areas identified in Stage 1 as being the most important and urgent (to begin soon)

We will build on the material previously collected by NIWA in 2014.

We have also been exploring how a web-based platform could be used to collate and present existing guidelines and other relevant information – a big thanks to Auckland Council for their assistance with this (a special shout out to Ken Williams).

The desired outcome from this process is to better understand:

  • What existing guidelines and methods are being used across the different geographic areas of NZ?
  • How up-to-date are they and/or are they meeting the needs of the sector?
  • What work is needed to get national consistency in each topic area?
  • What are the relative priorities across topics and within topics?

We are currently establishing a technical team to contribute to the above work – if you want to be involved in this process, please get in touch with us ASAP.

We also intend to establish a web-based discussion forum for this project at a later date – sign up to our email list to receive updates about this in due course.

Establishing a Steering group

Over the past few years, the work has been driven by various individuals and groups at various points of time, and has often involved volunteer-based committees. Given the scale of the project and the multiple interests involved, continuing to rely on this model presents a real risk that little progress will continue to be made. Water NZ is therefore establishing a Steering Groupto guide the work towards the ultimate objective of producing and rolling out nationally applicable rainfall and runoff guidelines. The immediate objective will be to agree on some priority projects and identify pragmatic ways to get the work started.

The Steering Group (and affiliations)

Mark Pennington,Tonkin + Taylor
Helen ShawEnvironment Canterbury
Nick BrownAuckland Council
Graham LevyBeca

IPENZ/Water NZ Rivers Group

Zeb WorthOpus

Water NZ Stormwater SIG

Nadia NitscheAuckland Council

Water NZ Modelling SIG

Assad ShamseldinUniversity of Auckland
Roddy HendersonNIWA
Martin DoyleTasman District Council
Central government representation To be confirmed

It was not the intention that the Steering Group be representative of all interests involved but rather to ensure any Steering Group has:

  • a mix of government (central and local), industry and science/academic perspectives;
  • strong technical knowledge and understanding; and
  • the drive to get the work done and hold others to account.

The individuals were mostly chosen from people who had made a notable contribution to the initiative to date.

For more information

Please get in touch with us to be added to the email list to receive periodic updates about this work. If you know others (members or non-members) who may have an interest in this work, please send them the link to this article.

The Water New Zealand contact for this work is Charlotte Cudby (Senior Policy Advisor) at or 04 495 0893.