Appendix 2: Further Information on Transpower’s Corridor Management Policy
The following provides a summary of the justification for the Corridor Management Policy zone approach.
Red zone
The red zone, measured 12 metres either side of the centre of the line, plus NZECP34 distances around support structures, represents the minimum reasonable distance required for access for maintenance and operations (ie, to work around foundations, use mobile plant or a four-wheel drive vehicle, etc). This results in protecting the ‘conductor shadow’ area from development. Access is most important around structures, but is also necessary along the whole length of the line so as not to restrict the range of vehicles/plant being used, and to allow for future movements of towers along the line route if necessary.
The red zone:
- is based on the requirements to maintain and operate 220 kilovolt flat-top towers – this distance would also incorporate other smaller line configurations
- is consistent with and incorporates most NZECP34 requirements – some additional area may be needed around the tower foundations (ie, where 12 metres from the foundation may be further than 12 metres from the centreline), and this would extend into the orange zone
- provides limited ability to alter existing line specifications (maintenance or upgrading) without adversely affecting activities underneath, or being constrained or affected by those activities
- is consistent with international good electrical industry practice.
Orange zone
The orange zone, occupies an additional 20 metres beyond the red zone. The red zone provides protection for access for maintenance/operation works, but does not incorporate other adverse environmental effects, including structural and safety risks, electromagnetic field effects, earth potential rise, amenity, effects on operational requirements, and efficient management of the network (not foreclosing the ability to upgrade lines). Thus a restricted discretionary zone where these matters can be considered is appropriate.
The 64-metre ‘zone of interest’ (12 metres plus 20 metres on either side of the centreline) is estimated to encapsulate approximately 80 per cent of line spans across the country.1 The zone approach provides for an appropriate buffer corridor that can be applied as one consistent rule. This distance is consistent with the width of easements that Transpower has obtained for significant line upgrades (eg the ‘ROX-ISL-A’ line, running from Roxburgh to Islington).
The ‘discretionary zone’, assessing specific proposals on a case-by-case basis, is also consistent with international practice, and enables any NZECP34 distances that extend beyond the red zone to be captured.
Green zone
The green zone extends beyond the orange zone (with no set distance). Transmission lines do not sit in a vacuum, but are located within, and have an impact on, a wider context/environment. Therefore, it is appropriate for Transpower to acknowledge the relationship between the existing lines and the surrounding environment.
Some activities located in the green zone may actually directly affect the lines; for example, plantation forestry (fall hazard from trees), quarrying (dust), and subdivision (with the potential for reverse sensitivity issues, including amenity). Options include applying orange zone processes (eg, for forestry or dust), or sending out information or educating developers on ways to screen new houses from existing lines (eg, for subdivisions nearby). The zone is not defined, and so appropriate action will be determined on a case-by-case basis.
1 NZECP34 Table 2: Safe distances from conductors.
