Dams Policy Information

Policy on Dangerous Dams, Earthquake-Prone Dams and Flood-Prone Dams

Horizons is required to update our existing policy on Dangerous Dams, Earthquake-Prone Dams and Flood-Prone Dams (the dams policy) which was adopted by Horizons in 2014. Since then, Building (Dam Safety) Regulations 2022 (the regulations) on dam safety have been released. Given the age of Horizons’ current policy and the new dam safety regulations, it is timely for the Horizons’ policy to be reviewed as it will be outdated once the regulations come into effect on 13 May 2024.

Section 161 of the Building Act 2004 (the Building Act) requires all regional councils to adopt a policy on dangerous dams, earthquake-prone dams and flood-prone dams.

The purpose of the policy is to help prevent the catastrophic failure of a potentially dangerous dam, and to ensure deficiencies in earthquake-prone or flood-prone dams are addressed, reducing the likelihood of significant harm and damage to people, property and the environment in the Horizons Region.

The Policy was adopted by Council on 28 May 2024. You can view a copy of the Dangerous Dams Policy here.

The regulations come into effect on 13 May 2024. From this date, owners of dams that meet the classifiable dam height and volume thresholds are required to classify their dam according to the potential impact of a failure of the dam, and have the classification audited and certified by a recognised engineer.

The recognised engineer certifies if the classifiable dam has a low, medium or high potential impact classification. The potential impact assessment considers the impact to the community, cultural sites, critical and major infrastructure, and the natural environment.

If it is a medium or high potential impact dam, the Building Act then requires the owner to prepare a dam safety assurance programme e.g. dam safety plans and dam inspections etc.

A classifiable dam (as defined in regulation 5 of the Regulations) is a dam that is four (4) metres or more in height and holding 20,000m³ or more in volume*.

*This definition was changed by the New Zealand Government on 28 March 2024 and comes into effect on 13 May 2024.

This proposed policy applies to dams that have a high potential impact classification or a medium potential impact classification and that are likely to fail in the ordinary course of events (“dangerous dam”), or a “moderate earthquake” or “moderate flood” (as defined in the regulations).

These terms are defined in the Building Act. The Building Act states that a dam is dangerous if it is:

A high potential or medium potential impact dam; and is likely to fail –

A dam is an earthquake-prone dam for the purposes of the Building Act if the dam –

a. Is a high potential impact dam or a medium potential impact dam; and

b. Is likely to fail in an earthquake threshold event (as defined in the regulations).

A dam is a flood-prone dam for the purposes of the Building Act if the dam -

a. Is a high potential impact dam or a medium potential impact dam; and

b. Is likely to fail in a threshold event (as defined in the regulations).

The dam owner or recognised engineer must immediately notify Horizons if they believe a dam is dangerous, earth-quake prone or flood-prone.

The policy sets out what Horizons will do if we are notified of a dangerous dam, earthquake-prone or flood-prone dam in our region.


The policy has three key sections:


1. How we will perform our legislative functions in relation to dangerous, earthquake-prone or flood-prone dams.

We have a variety of functions under the Building Act, and our approach is explained in more detail in the policy.


2. Our priorities when performing these functions.

The policy sets out that we will prioritise safety at all times, following a risk-based approach. When undertaking our functions, we will also protect the health and wellbeing of the environment and have regard to cultural and heritage values.


3. How the policy will apply to heritage dams.

If a dangerous dam has been classed as a heritage dam, we will account for the need to facilitate the preservation of significant heritage values.

The policy does not apply to all dams or farm ponds. It only applies to classifiable dams that are either a high potential impact dam or a medium potential impact dam that are likely to fail in the ordinary course of events (“dangerous dam”), or a “moderate earthquake” or “moderate flood” as defined in the Building Act.

The policy does not classify dams. The regulations require the owner to classify their dam according to the potential impact of a failure of the dam, and have the classification audited and certified by a recognised engineer.

The policy also does not cover consenting matters under the Resource Management Act 1991.

Submissions should relate to the contents of the dams policy. Horizons Regional Council is not able to change anything in the Building Act or the Building (Dam Safety) regulations.

Where can I find more information?

For more information about classifiable dams and dam safety, please visit MBIE's Building Performance website.

Dam safety frequently asked questions are available on Waikato Regional Council's website.

Dams Policy Submission Form

Consultation closed on 22 April 2024.

Anyone can make a submission on the proposed policy. Submissions should relate to the contents of the dams policy. Horizons Regional Council is not able to change anything in the Building Act or the Building (Dam Safety) Regulations.

Horizons will receive submissions:

  • Online by: submitting the form below.
  • By post to: Private Bag 11025, Manawatū Mail Centre, Palmerston North 4442.
  • In person: drop a form off at one of our offices.

Please note, the contents of your submission will be made public through council agendas and as a result will be published on our website. If you wish to have your name and contact details removed, please email district.advice@horizons.govt.nz.