Dangerous Dams Policy

Adopted 7 November 2006

The Building Act 2004 covers dam construction and safety management for large dams. It ensures the structures are well built, that larger dams are regularly monitored and the potential risks to people and property are minimised. Regional Councils are given the task of issuing building consents for dams, and ensuring they pose no risk to the public.


Download the Dangerous Dams Policy (266KB PDF).

Dam safety

Dam safety has been a concern for a number of years and this has been brought to a head by the Opuha Dam incident in 1997 and flood events of the late 1990s and in 2004. The risk factors for a dam can change over time, and there are currently no systems in place to recognize this. A dam’s continuing safety can be dependent on site conditions, the effectiveness of maintenance and natural hazards, with flooding being the main threat.

Like many other structures, all building work on dams is covered by the Building Act. However, the Act also introduced some specific safety requirements for large dams.

Affected dams are affected

Within the Nelson City boundary there are very few dams. However, for a rough guide, if your dam is capable of holding 20,000 or more cubic metres (about the capacity of 5 to 6 Olympic sized swimming pools) and is 3 or more metres deep, the Dam Safety Scheme will affect the dam. Smaller dams are not affected by the Dam Safety Scheme.

Who's responsible

The new legislation sets out clear functions and responsibilities for both larger dam owners and regional authorities in regard to the Dam Safety Scheme. Some of the new responsibilities must now be written into Regulations to be prepared by Government, so they can be implemented.

Nelson City Council will identify and assess dams which could fall within the definition of a high potential impact dam or a medium potential impact dam. Inspect where necessary, require owners to carry out initial evaluation to ensure it is not leaky and also require owners to prepare a detailed assessment of the dam’s performance under a moderate earthquake or flood.

Contact us

For more information on the Dangerous Dams Policy please contact Manager Building Unit, +64 3 546 0200.


dangerous-dams-policy.pdf (pdf, 266 KB)