Dam safety under the Building Act
The Building Act 2004 (the Act) introduces new requirements for dam construction and dam safety management.
Dam safety has been a concern for a number of years. This was brought to a head by the Opuha Dam in South Canterbury failing during construction in 1997, various flood events around the country during the late 1990s and there were serious concerns that a river-fed reservoir dam above Picton might not cope with extreme rainfall that had caused floods in the township in February 2004. Scientific evidence of climate change indicates changed future weather patterns for New Zealand, with rising temperatures, increased rainfall and increased extreme weather events potentially increasing the flood flows that dams will need to accommodate without failure. The potential impact factors for a dam can change over time and there are currently no regulatory systems in place to recognise this.
Dam failure could result in significant damage to life, property, infrastructure and the environment. Like other buildings, all building work on dams is covered by the Act. The Act also includes some safety requirements for dams.
The dam safety scheme will help ensure the safety of large dams and provide community confidence that dams in New Zealand are built well, managed correctly and adequately maintained.
Karapiro Dam on the Waikato River
Overview of the dam safety scheme
Regulations for the dam safety scheme are currently being developed and are intended to take effect in early 2010. The scheme will apply to dams that meet the definition of a dam as prescribed by the Act. It will ensure that these dams have a formal system of dam monitoring, inspection and maintenance.
The scheme will require that large dams be classified as a low, medium or high potential impact dam and registered with the regional authority for their area.
Medium and high potential impact dams will require a dam safety assurance programme, and an annual certificate of compliance with that programme.
Need for a dam safety scheme
The intent of the Act is to encourage better practice in building design, construction and regulatory building control. This means that all buildings (including dams) should be designed and built properly the first time.
The Act aims to provide a clear and comprehensive regulatory scheme for ongoing dam safety management, particularly for dams whose failure would put populations at risk downstream of the dam and would cause major damage to property, infrastructure or the environment.
Several important factors influenced the Government’s decision to introduce a regulatory scheme for larger dams:
- Dams sometimes fail and there is the potential for loss of life and property damage.
- Once constructed and commissioned, dams need ongoing monitoring, maintenance and repair to maintain their integrity.
- A more structured and formal system of compliance monitoring is needed to ensure the safety of dams, in light of the changing nature of public ownership and commercial arrangements for owning, operating and managing dams.
Inside a gallery at Whakamaru Dam on the Waikato River
Definition of a large dam
As a rough guide, if a dam is capable of holding 20,000 or more cubic metres (about the size of eight Olympic-sized swimming pools) and of retaining 3 or more metres’ depth of water, it will be covered by the dam safety scheme.
The dam safety provisions of the Act and related Regulations will generally not apply to dams capable of holding less than 20,000 cubic metres of water. However, even with small dams or stopbanks, other requirements of the Building Act still apply, such as that building work needs a building consent, and that finished work must meet the performance standards of the Building Code.
Section 7 of the Act gives a precise definition of the type of dam that will trigger the provisions of the new scheme, including flood control dams, significantly modified natural features and canals.
Section 7 states that a ‘dam’:
(a) means an artificial barrier, and its appurtenant structures, that –
(i) is constructed to hold back water or other fluid under constant pressure so as to form a reservoir; and
(ii) is used for the storage, control, or diversion of water or other fluid; and
(iii) retains 3 or more metres’ depth, and holds 20,000 or more cubic metres volume, of water or other fluid; and
(b) includes –
(i) a flood control dam; and
(ii) a natural feature that has been significantly modified to function as a dam; and
(iii) a canal; but
(c) does not include a stopbank designed to control floodwaters.
To work out if the Act may apply to your dam, look at Figure 1 and Figure 2 below. This figure is illustrative only. It shows that a dam designed to hold 20,000 cubic metres of water is a large structure and the area of the reservoir would be significant.
Figure 1: Cross-section of a Dam
Figure 2: Plan view of a Dam
Figure 3 illustrates that at minimum, a dam affected by the dam safety scheme is similar in size to a rugby field filled up the crossbar.
Figure 3: Rugby field comparison
The Department will develop further guidance material on dam classification once the dam safety scheme’s Regulations are approved.
Number of large dams
An estimated 1150 dams meet the definition of a large dam. About 700 of these are council reservoirs or power generation dams and about 50 are privately owned power generation dams. The remaining 400 are on rural properties – farm, irrigation, reservoir/fire-fighting, effluent dams etc.
Requirements for large dam owners
Many large dams already have safety management programmes, and these are still relevant. However, there is currently no formal system of dam monitoring, inspection and maintenance. Owners of large dams will be required to classify and register any large dam on their property within 3 months of the regulations taking effect in late 2009 or, if the dam is being built during that time or later, within 3 months of the dam being commissioned.
The Act requires dam owners to:
- assess their dams against regulatory standards and classify dams as having low, medium or high potential impact. The different levels of classifications refer to the potential impact to the inundation area and people in the area if the dam were to fail or break and release the reservoir. The dam classification must be certified by a ‘recognised engineer’ ( to be defined in the Regulations)
- register the dam and its classification with the appropriate regional authority
- for medium and high potential impact dams, to prepare and submit to that regional authority a dam safety assurance programme
- to provide ongoing evidence of implementing surveillance and maintenance procedures in accordance with their approved safety assurance programme by submitting an annual compliance certificate
- to seek advice from a recognised engineer with suitable qualifications to certify audits of the safety assurance programme.
Most dam owners will be able to work out whether their dam meets the definition of ‘dam’ under the Act. A dam owner will, however, need a recognised engineer to assist with ascertaining the dam’s potential impact category.
Face of the Whakamaru Dam on the Waikato River
Compliance costs
A ‘dam’ as defined by the Act will incur costs for engaging a recognised engineer to review information, confirm the classification of the dam and, if required, prepare a dam safety assurance programme.
There is also likely to be a charge payable to the regional authority for approving the classification of the dam and, if required, its dam safety assurance programme.
The Department aims to provide sufficient information within the proposed Regulations on classification, registration and the preparation of dam safety assurance programmes (if required) to help make compliance as simple as possible.
‘Recognised engineers’
Dam owner obligations under the Act require the exercise of professional knowledge and judgement. The Act requires that classifications and safety assurance programmes are certified by a ‘recognised engineer’. These requirements are intended to ensure that a dam is correctly classified and that a safety assurance programme has been prepared and audited by an appropriately qualified professional. Regulations will define the qualifications and competencies of ‘recognised engineers’.
Costs to accredited dam owners
The Act allows dam owners to become accredited for the tasks relating to the classification and management of dam safety assurance programmes. Becoming an accredited dam owner will be voluntary.
Accredited dam owners will be exempt from the need to seek approval of a dam safety assurance programme from a regional authority because the owner’s processes and procedures will be formally accredited. Future regulations are intended to implement the accreditation scheme.
Relationship with the Resource Management Act 1991
Some dam owners have resource consents under the Resource Management Act 1991 for operating their dams. These cover the control of taking, using, damming and diverting water, and controlling the quantity, level and flow of water. Some existing conditions of a resource consent may require a dam owner to monitor, audit and implement dam safety assurance programmes, as anticipated through the dam safety provisions of the Building Act.
The new regulatory scheme for dams under the Act is being designed to complement the provisions of the Resource Management Act 1991. It is anticipated that, for dams constructed and commissioned after 31 March 2005, the provisions of the Building Act may reduce or remove the need for resource consent conditions to be imposed.
Face of the Karapiro Dam on the Waikato River
Effect of the scheme on regional authorities
Regional authorities (regional councils and unitary authorities [regional and city councils]) must be accredited and registered as building consent authorities to carry out their dam-related responsibilities. The Building Controls newsletter Codewords No.8, Oct/Nov 2005 includes an article on how the Building Act clarifies the role of territorial authorities and regional authorities in relation to dams, particularly their responsibility for consent processing, inspecting and monitoring compliance with the dam safety scheme.
The Act requires regional authorities to:
- after 30 June 2008, provide building consent processing and inspection services for dams, such as issuing project information memoranda (PIMs), building consent processing, compliance monitoring and enforcement of the Building Code and Regulations
- administer and monitor the dam safety scheme, which means that regional authorities hold a register for dams, consider and approve or refuse dam classifications (based on whether they have been certified by a recognised engineer as will be defined in the proposed Regulations), approve or refuse dam safety assurance programmes, and issue dam compliance certificates
- adopt and implement a policy on dangerous dams, establishing the nature of processes and procedures that would be triggered for medium or high potential impact dams (based on potential impact categories [PIC] as will be defined in the proposed Regulations) in circumstances of likely collapse in a moderate flood, a moderate earthquake or if the dam is leaky.
Dangerous dams
The Act’s requirements for regional authorities to develop a dangerous dams policy in order to reduce the risks of dam failure over time and came into effect in late 2006.
Section 153 of the Act states that a dam is ‘dangerous’ for the purposes of the Act if it:
(a) is a high potential impact dam or a medium potential impact dam; and
(b) is likely to collapse –
(i) in the ordinary course of events; or
(ii) in a moderate earthquake (as defined in the regulations); or
(iii) in a moderate flood (as defined in the regulations);
The purpose of the dangerous dams policy is to set a minimum benchmark against which dams should not collapse.
Consultation
Summary of submissions – available from September 2007
In late June 2006, the Department of Building and Housing issued Regulations for the Dam Safety Scheme: Discussion Document. Responses were received from 58 organisations and individuals representing dam owners/operators or users, regional and territorial authorities, consultants, professional bodies, non-government agencies, government agencies and one individual.
Stakeholders expressed clear support for the proposed Regulations, with a number of comments made about minor technical issues and definitions. The Department has consulted the Regional Authority Working Group (RAWG) to ensure these issues are incorporated, where appropriate, into the final proposals.
The RAWG represents three regional councils, the Ministry of Agriculture and Forestry, Federated Farmers, New Zealand Society On Large Dams, a large dam owner and an energy company. Consultation with the RAWG has helped the Department identify operational issues in the transitional period of the scheme, and in analysing issues raised in submissions on the discussion document.
A summary of submissions on the discussion document can be viewed.
Copies have been sent to all key stakeholders and submitters. The Department thanks all submitters for their contributions.
If you have any queries relating to the dam safety scheme, please contact:
Hassan el Maaroufi
Advisor, Operational Policy
Department of Building and Housing
DDI +64 4 496 4732
Fax +64 4 494 0290
Email: Hassan.el.maaroufi@dbh.govt.nz