4 Transpower’s Corridor Management Policy
The Corridor Management Policy (CMP) was developed in response to the limitations of the New Zealand Electrical Code of Practice 34:2001 (referred to as NZECP 34) in managing the risks posed by third-party development near the transmission network. The CMP provides a policy framework for managing and protecting Transpower’s transmission corridors. The CMP is Transpower’s internal policy which guides the company’s input to plan development and submissions on specific development and activity proposals including proving its affected party approval, lodging submissions, or appealing resource consents. As a company policy, it does not hold any statutory weight. However, when adopted into district plans as an appropriate method to manage the issue of third-party risks to transmission lines, the approach holds the same status as other district plan rules. Either Transpower or your local authority can provide information on how this policy might affect existing use rights.
The CMP provides a consistent and rational basis for managing the issue of development near transmission lines. A nationally consistent approach is warranted because the effects of the lines do not vary across the 12,000-kilometre network, even though the receiving environment might. It is therefore just as important to consider the full suite of risks in rural Southland as in urban Auckland. Because of the sheer scale and national nature of this issue, a consistent approach is appropriate.
The objectives of the CMP are to:
- protect, through appropriate mechanisms, the land immediately under existing lines from activities that undermine the safe and efficient operation, maintenance and upgrade of existing lines – this can be achieved by seeking clear space immediately under transmission lines, to a distance of 12 metres either side of the centre of the line, as well as all relevant NZECP34 distances1 (the ‘red zone’)
- manage, through appropriate mechanisms, activities within close proximity of transmission lines, to a distance of 20 metres either side of the red protection zone (the ‘orange zone’)
- inform, educate or liaise, where relevant, where issues are raised by development occurring beyond the orange zone but in proximity to transmission lines (the ‘green zone’), although orange zone provisions may still be relevant outside of the set distance of the orange zone.
These zones are illustrated in Figure 2.2
Figure 2: Transmission Corridor Activity Management
Read a text description of this figure
This image graphically presents the Transmission Corridor Activity Management zones. A tower or pole and transmission lines are surrounded by:
- A red zone – measured 12 m either side of the transmission line + relevant NZECP34 distances around structures and conductor swing
- An orange zone – measured 20m either side of the red zone (including relevant NZECP34 distances)
- A green zone – no restrictions (relevant NZECP34 restrictions still apply)
The policy is based on the specific effects of development and activities on the network, and managing the effects of the network on those activities. Different types of activities are considered against the following key criteria:
- risks of electrical hazard or injury
- risks associated with ‘reverse sensitivity’ issues
- maintaining a level of amenity
- risks of disruption to transmission and effects on security of supply
- physical risks to structural integrity
- risks to the ability to inspect and maintain lines and support structures and to undertake line upgrades.
The details of the policy were developed by Transpower’s transmission experts and practitioners after considering anecdotal evidence, experience, specific examples, practices and case studies across the network (ie, on a national basis).
The red zone was agreed to as the minimum distance that could reasonably accommodate the heavy machinery required to undertake line maintenance works. It was agreed that to reduce risk of injury to persons, or damage to property, and to enable necessary maintenance and operational requirements, it was not appropriate for any development to occur in this zone. This analysis also included a review of international practice, which concluded that it is very unusual (and not good engineering practice) to allow buildings and structures (including, but not limited to, residential use) to develop near to existing high-voltage transmission lines.
A more considered approach was felt to be appropriate for a wider area either side of the red zone. Experts’ experience concluded that development proposals need to be taken on their merits in this zone, as some development may be appropriate with certain measures in place to mitigate additional electrical risk, accommodate future line upgrades, provide a level of amenity, etc. Thus it was considered a zone of 20 metres either side of the red zone would capture approximately 80 per cent of the conductor swing distances for spans along the 12,000- kilometre network. This approach is also consistent with the distances of easements obtained for significant line upgrades.
Further details of the justification for the CMP zones is provided in appendix 2.
