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Planning for Development of Land on or Close to Active Faults

1 Introduction

2 Principles for Planning Approaches

3 Understanding Earthquakes and Active Faults

4 Taking a Risk-based Approach

5 Mapping Active Faults

6 Fault Avoidance Zones

7 Fault Recurrence Interval

8 Fault Complexity

9 Building Importance Category

10 Planning for Fault Rupture Hazard

11 Taking a Risk-based Approach to Resource Consents

12 Case Studies - Implementing the Guidelines

13 Acknowledgements

14 Further Reading

Appendix 1: Classification of Faults

11 Taking a Risk-based Approach to Resource Consents

11.1 Determining consent categories

Determining consent categories for buildings within a fault avoidance zone involves evaluating the fault recurrence interval, fault complexity, and Building Importance Category alongside the risk the community is prepared to accept.

Differing types of buildings will be placed into different resource consent activity categories, based upon the risk. The council needs to be satisfied that the risk is not significant, or that appropriate mitigation measures have been taken, before granting resource consent.

As the risk increases, the consent category should become more restrictive, and the range of matters the council needs to consider will increase. The council needs to set requirements for the bulk, location and foundations of any structure, so it can impose the consent conditions that will avoid or mitigate the adverse effects of fault rupture.

If the overall risk is low, the provisions contained in plans may be more permissive and make use of the permitted or controlled activity consent categories. If the risk is high, then planning provisions in plans become more restrictive and greater use made of discretionary and non-complying activity consent categories.

A rule may require resource consent for a new building, but with a requirement that a geotechnical report be included with the application (confirming that the building will be located at least 20 metres from an area subject to fault rupture, or that necessary engineering precautions have been taken).

For example:

• "For all structures and buildings, an engineering report will be required to confirm that the Wellington Fault is not within 20.0m of any proposed structure or building; or that the necessary engineering precautions have been taken" (Standard 14H 2.1.1.2 to Rule 14H 2.1 of the Hutt Proposed District Plan).

Each council will want to apply the resource consent activity status categories that suit its own circumstances. The key is to ensure that the council has the ability to address the fault rupture hazard risk properly when assessing a resource consent application. The matters over which the council can reserve control or restrict its discretion include:

• the proposed use of the building
• site layout, including building setback and separation distance
• building height and design
• construction type (for resource management purposes)
• financial contributions (for example, reserves contributions).

Tables 11.1 and 11.2 show an example of resource consent activity status for proposed buildings within a fault hazard avoidance area. The activity status will depend on the Building Importance Category, the fault recurrence interval, and the fault complexity.

Table 11.1: Resource consent activity status for greenfield sites

Note: Faults with a recurrence interval of greater than 125,000 years are not considered active.

* The activity status is permitted, but could be controlled or discretionary because the fault location is well defined.

** Although the activity status is permitted, care should be taken in locating BIC 4 structures on or near known active faults. Controlled or discretionary activity status may be more suitable.

= Where the fault trace is uncertain, specific fault studies may provide more certainty on the location of the fault. Moving the fault into the distributed or well defined category would allow a reclassification of the activity status and fewer assessment criteria.

Italics show that the activity status is more flexible. For example, where discretionary is indicated, controlled activity status may be considered more suitable.

Table 11.2: Resource consent activity status for developed and already subdivided sites

Note: Faults with a recurrence interval of greater than 125,000 years are not considered active.

* The activity status is permitted, but could be controlled or discretionary because the fault location is well defined.

** Although the activity status is permitted, care should be taken in locating BIC 4 structures on or near known active faults. Controlled or discretionary activity status may be more suitable.

= Where the fault trace is Uncertain, specific fault studies may provide more certainty on the location of the fault. Moving the fault into the Distributed or Well Defined category would allow a reclassification of the activity status and fewer assessment criteria.

Italics - show that the activity status is more flexible. For example, where discretionary is indicated, controlled activity status may be considered more suitable.

Note that the restricted discretionary category has not been shown in Tables 11.1 and 11.2 but may be considered more effective than the non-complying activity status as it allows for targeted assessment criteria to be developed.

11.2 Exercises

Example 1

A developer with a Greenfield site proposes to build a Building Importance Category 2a structure (a typical New Zealand wood-framed house) within a fault avoidance zone. The fault through this zone has a Fault Recurrence Interval Class of III (>3500 to ≤5000 years) and the Fault Complexity is A (well defined).

Q: What type of resource consent would have to be applied for?

A: __________________________________________________1

Example 2

A philanthropist decides to make use of a spare plot of land she owns to build an art gallery to display local work. The site is located within a densely built-up inner city suburb in a fault avoidance zone. The proposed art gallery will have a floor area of 700m2 (refer to section 9.1 of this report to determine the Building Importance Category). The Fault Recurrence Interval Class is III and the Fault Complexity is B.

Q: What type of resource consent would have to be applied for?

A: __________________________________________________2

Example 3

The philanthropist decides to move the proposed gallery to the country, where she owns 20 hectares of undeveloped rural land. The proposed location is within a fault avoidance zone where the Fault Recurrence Interval Class is II and the Fault Complexity is C?

Q: What type of resource consent would have to be applied for?

A: __________________________________________________3

Example 4

A local health care facility is proposed that will accommodate up 60 elderly patients who will live at the facility (refer to section 9.1 of this report for the Building Importance Category). The proposed site is in a rural area that has recently been subdivided into five-acre blocks, and is within a fault avoidance zone. A well-defined active fault with a 4000-year fault recurrence interval runs through the site.

Q: What type of resource consent would have to be applied for?

A: __________________________________________________4

11.3 Answers

1. Permitted* activity (but a district plan may want to make this activity controlled or discretionary given that the Fault Complexity is well defined).
2. Permitted. The building is a Building Importance Class 2b structure (defined as either a retail building less than 10,000m2, or a public assembly building less than 1000m2) to be located where the Fault Recurrence Interval is greater than 3500 but less than 5000 years (Class III) and the Fault Complexity is distributed (B).
3. Non-complying activity. The activity is proposed where the Fault Recurrence Interval is greater than 2000 but less than 3,500 years (Class II), the Fault Complexity is uncertain (C) and the building is a Building Importance Class 2b structure (defined as either a retail building less than 10,000m2, or a public assembly building less than 1000m2). The activity is classed Non-complying as the site allows for alternative siting of the gallery outside the fault avoidance zone - which would reduce the risk to life and property.
4. Non-complying activity. The Fault Recurrence Interval Class is III (greater than 3000 but less than 5000 years), the Fault Complexity is A (well defined) and the building is a Building Importance Class 3 (a health care facility with a capacity of 50 or more residents but does not have surgery or emergency treatment facilities).

11.4 Assessment criteria

Where there are rules in a district plan limiting development in a Fault Avoidance Zone, the district plan needs to include assessment criteria that make clear what the council will consider when assessing resource consents. Matters may include:

• the risk to life, property and the environment posed by the natural hazard
• the likely frequency and magnitude of movement
• the type, scale and distribution of any potential effects from the natural hazard
• the effects of ground shaking and ground displacement caused by earthquakes
• the distance of any proposed structure from the fault (as shown on either the district plan map, or from a site-specific study locating the fault trace)
• the degree to which the building, structural or design work to be undertaken can avoid or mitigate the effects of the natural hazard
• the accuracy and reliability of any engineering and geotechnical information (eg, the extent to which such a report shows how the risk of building failure following fault rupture can be reduced to minimise the effects of the fault rupture on the safety of occupants and neighbours).

If the council has not located the fault trace, and the developer does not wish to locate it, the developer needs to prove that the building is resilient enough to withstand fault rupture.

11.5 Assessment of Environmental Effects requirements

An applicant lodging a resource consent application to build on or near an active fault is required by section 88 of the Resource Management Act 1991 to provide an adequate Assessment of Environmental Effects (AEE) with any application. The district plan needs to spell out what is required of the resource consent applicants.

An AEE should:

• consider alternatives
• provide a risk analysis
• identify the hazard
• show mitigation measures.