4. Mitigation Measures

As outlined above, the diversion of the Huia 2 watermain as part of the Mt Eden Enabling Works will impact seven trees within Fenton Street. In order to mitigate the effects of tree removal on the local streetscape, the following mitigation measures will be implemented during the Mt Eden Enabling Works.

4.1 Trees Requiring Removal

4.1.1. Transplanting Trees

Transplanting the seven pohutukawa trees was considered, however, the timing of the works means that they would be transplanted during the late summer months of Q1 2020, which would affect the potential for these trees to survive the process. Auckland Council during consultation (November, 2019) have indicated that the removal of the trees and their replacement with a healthy tree in an appropriate location would be a better outcome than transplanting the current trees.

4.1.1. Permanent Removal and Replacement

It is known that it will not be possible to replant the trees in the same location, therefore, replacement trees will be planted in an appropriate location elsewhere within the CRL designation. The locations of replacement trees will be included in a replanting plan prepared as part the Urban Design DWP for the public realm reinstatement works. The Urban Design DWP and replanting plans will consider the following in accordance with designation condition 55.3(c):

Replanting of removed trees at a ratio of at least 1:1. Document input from the Auckland Council Parks Department (now Auckland Council Community Facilities) with regard to tree species / vegetation selection, tree pit construction and positioning of replacement trees. An outline of the maintenance periods and responsibilities for care of the trees (i.e. maintenance is to be undertaken by the Requiring Authority for a period of five years for specimen trees and 3 years for all other landscape planting). Any consultation undertaken in relation to the replacement planting (refer to Section 5 of this TV DWP).

4.2 Trees not Requiring Removal

On review of the current work plans it is not anticipated that tree (root or canopy) protection will be required for the Mt Eden Enabling Works. However, there are trees present along Wynyard Road and Normanby Road. It will be the Project Arborist’s responsibility to verify that this assumption is correct as works progress. If the Project Arborist identifies that tree protection is required the Council Arborist will be informed and offered the opportunity to undertake a site walkover to review the approach to tree protection and to inspect its implementation. If the Project Arborist identifies that trees will require pruning these works will be registered with the council call centre as a request for tree maintenance as far in advance as possible.

If it is determined that tree protection is required, guidelines are provided in Section 4.2.1.

The Tree Protection Zone encompasses the root and crown area of the tree that would need to remain isolated from construction disturbance to maintain tree health. The height of the Protection Zone is dictated by the height of the tree and the width (or radius) around the tree is typically calculated by multiplying the tree’s diameter at breast height (DBH) by 12 (AS 4970-2009):

Tree Protection Zone = DBH x 12

The Tree Protection Zone will not be less than 2m nor greater than 15m, except where crown protection is required.

If a tree is multi-stemmed at 1.4m above the ground (refer to Figure 4-1) the Australian Standard (AS4970-2009) indicates that in this situation the following equation should be used to determine the DBH, which would then feed into the equation above to calculate the Tree Protection Zone:

Figure 4-1: Tree forks below 1.4m where the arborist would measure DBH (AS4970-2009).

Crown protection may also be required to ensure that the trees do not receive injury from machinery such as excavators, drilling rigs, cranes, trucks and hoarding installation. Crown protection will be located 1m outside of the perimeter of the crown, which may be within the Tree Protection Zone.

Figure 4-2: Indicative Tree Protection Zone (AS4970-2009).

The following activities will not be permitted in the Tree Protection Zones:

Mechanical excavation on the road, footpath or any public space. Stockpiling of building materials, debris or soil. Vehicular traffic except on existing paved surfaces. Installation of service pits or hatches. Vehicular crossings. Severing of tree roots with a diameter greater than 30mm.

Alteration of soil levels and structure.