Managing Specific Natural Hazards

Introduction

The following section sets out how specific hazards can be managed through RMA plans.

The primary classes of natural hazards in New Zealand are:

• earthquake/seismic
• landslip/landslide/land instability/subsidence
• coastal
• flooding
• geothermal
• meteorological
• tsunami
• volcanic.

An overview of these hazard classes and the principal means for managing them across the 4Rs is contained in the National Hazardscape Report (2007). They are referred to here as classes in that, for effective management, a specific hazard or risk by location must be considered. For example, the Hutt Valley flood hazard is not the same as the Matuara River flood hazard as a different set of risks are involved in each case.

Generally, resource management plans can contain objectives, policies and rules to manage:

• the effects of hazards themselves (such as coastal erosion)
• the effects of land use on hazard risk (such as the removal of dune vegetation)
• the effects of treating hazard risk (such as the loss of coastal access following the construction of a seawall).

The management response for specific natural hazards is highly dependent on the nature, location and effects of the particular hazard, and the community in which the hazard is located. No one policy response to natural hazards can address all hazards or all locations. Natural hazards policy should consider adapting the 'best fit' hazard response to the nature of the particular hazard relative to its location, recognising that the methods (or mix of methods) used to address the risk will often be different.

Many local authorities take an ‛all-hazards' approach to developing hazard-related objectives and policies in their plans. This provides simplicity and may be acceptable for an overall hazard objective and some policies. However, a hazard-specific approach is likely to be more effective and easier to implement and monitor as the guidance it provides to those making decisions on, or monitoring, resource consents is more likely to be stronger, clearer, and more targeted towards the issues that need to be dealt with.

Plan provisions should focus on the effects that need to be addressed to achieve natural hazard objectives, and state how those effects are going to be dealt with. Plan provisions should also provide for a review of current policy where increased knowledge of a hazard becomes available.

Earthquake/seismic

New Zealand has earthquake hazards that can impact on the built environment in a number of ways including, shaking, liquefaction and mass movement.

A fault is a fracture in the Earth's crust. Opposite sides of the fracture are held together by pressure and friction, but as stress builds up a fault may suddenly rupture. In a large rupture, shock waves cause the earth to shake violently and produce an earthquake. An active fault is a fault that has ruptured repeatedly in the past, and whose history indicates that it is likely to rupture again. Active faults include faults that weren’t previously identified. An active fault therefore creates a fault hazard risk.

When the ground shakes, and/or when there is surface rupture on a fault line causing ground deformation, there is likely to be damage and/or destruction of structures built across the fault line or within the crush zone. Earthquakes may also trigger other hazards, such as liquefaction, tsunami, landslides, and flooding.

Councils can plan for active faults through the identification of active faults on planning maps, with specific rules that limit development in higher risk areas.

Landslip/landslide/land instability/subsidence

Land instability includes landslides, subsidence, and issues around alluvial fans. There are many types of landslides, including earth flows, topples, debris flows, rock falls, block slides, debris avalanches, lateral spreads, and rotational and translational landslides. The most common trigger of landslides is prolonged or intense rainfall, however large earthquakes, volcanic eruptions and geothermal activity can also trigger landslides.

Land instability can result in threats to life, property, and infrastructure. In hilly or mountainous areas with limited access, landslides and landslips can isolate communities and have disruptive side effects such as clogging water treatment facilities with silt.

The general approach taken in plans to landslides, land instability or subsidence is to reduce the risk and avoid activities in areas prone to these hazards. RMA plan provisions (typically district plans) can manage the hazard risk through:

• the identification and mapping of areas of land instability
• zoning to avoid development in areas subject to the hazards
• requiring site investigations and/or possible engineering works to assess and reduce risk in areas of identified land instability where avoidance is impractical or not warranted
• developing rules and standards to assess consents for activities in areas prone to these hazards.

Where risks are identified in policy statements and plans, councils should adopt a precautionary approach to development.

Guidelines for assessing planning policy and consent requirements for landslide prone land have been published that detail how a risk-based approach can be taken to planning for land instability risk, plan methods that could be employed, and mapping of land instability risk. 

 

 

Coastal hazards

Coastal hazards include storm surge, coastal erosion, sea-level rise, coastal flooding, and tsunami. These are all natural processes that become a hazard where they pose a threat to property and life.

The NZCPS 2010 aims to ensure that coastal hazard risks are managed by locating new development away from areas prone to coastal hazard risk, considering responses for existing development in coastal hazard areas and protecting or restoring natural defences to coastal hazards. Regional policy statements, regional plans and district plans are required to give effect to the NZCPS 2010.

Coastal hazards are generally well recognised in existing RMA plans with provisions aimed at managing coastal erosion and the inundation of land from coastal flooding, storms and sea-level rise.

There are a range of methods available for managing coastal hazards through resource management plans, including:

• mapping where coastal erosion will occur in the future (hazard zones)
• setting back buildings an appropriate distance from the shoreline to minimise risk from erosion (building setbacks)
• placing only appropriate structures (for example, relocatable buildings) not key facilities in areas of known risk
• restoring sand dunes and vegetation which provide protection from the sea via a buffer zone
• removing structures from areas of risk via a programme of managed retreat
• installing engineered protection in the form of appropriate seawalls and rock walls
• beach nourishment (introducing extra sand to a beach system)
• doing nothing and letting the sea dictate.

Plans may identify and map areas that are subject to coastal hazards and include objectives, policies and methods, and standards that look to:

• reduce the risk of coastal hazards (such as through directing sensitive developments away from hazard prone areas)
• manage effects of, or effects of development on, hazards
• provide buffer areas between development and areas of high hazard risk
• identify engineering solutions
• control activities by consent activity status and using standards.

In areas subject to existing or new development, councils should consider both structural and non-structural options to managing coastal hazards. Coastal plans should provide guidance when considering which option is appropriate.

There is on-going debate about the best methods for determining the positioning of hazard zones and setback zones. As there is no one fit-all approach for coastal areas, councils need to determine the appropriate hazard and setback zones for their particular section of the coast.

A methodology for identifying hazard zones and setbacks should take into account the physical characteristics of a location, the quality of information available regarding the particular hazard, and the resources and expertise available. The hazard zone should be able to be easily understood by the community. EnviroLink has produced a guide to good practice – Defining Coastal Hazard Zones for Setback Lines (PDF) which focuses on approaches to defining present and future coastal hazard exposure as an input to development setbacks to manage risk from coastal-related hazards and the effects of climate change.

Details on how to incorporate climate change effects and sea-level rise into planning for coastal hazards can be found in the Ministry for the Environment publication Coastal hazards and climate change: a guidance manual for local government in New Zealand.

Flooding

Flooding in this context is defined as the inundation of land by water. Coastal flooding is addressed in the coastal hazards section.

The magnitude of the flood risk is dependent on the probability of a flood occurring, the value and type of assets or resources exposed to the risk, and the vulnerability of those assets or resources to damage.

The effects of flooding include the movement of debris, the build-up of debris against structures, silt and/or mud deposition, erosion, and water damage to buildings and vehicles. Consequential contamination and health effects may arise from overloaded sewerage systems or transportation of hazardous substances.

Flooding can be caused by a range of factors and circumstances including:

• high, or particularly intense, periods of rainfall
• snowmelt (which may also coincide with high rainfall)
• blocked waterways or drainage systems (including natural damming after landslips or earthquake, or vegetation blocking drains, creeks or streams).

Human activity can also contribute to, or exacerbate, flood hazards by, for example:

• obstructing natural overland flow paths (such as by placing buildings, raised roadways, embankments and other similar obstacles in the flow path or flood channel)
• increasing the flow of water into natural or man-made drainage systems (removing vegetation, increasing areas of impermeable surfaces, or increasing the number of stormwater outlets, and thereby the amount of stormwater, that enters a particular drainage system).

There are many ways to mitigate the flood risk, but generally they fall into two groups:

• structural works: designed to contain floods and to limit erosion and deposition by controlling river behaviour
• non-structural methods: including land-use planning, emergency management planning, and flood-proofing of buildings. These methods are designed to either remove people and assets from risk or to manage exposure to flood effects.

In the main, RMA plans primarily address non-structural methods. However it is important that those preparing plans are mindful of structural works and the possible need to accommodate them when drafting plans. Plan provisions may need to consider such matters as the placement, building, maintenance, operation and protection of structures such as stopbanks, weirs, groynes, flood gates, diversions, or other flood protection measures when writing objectives, policies and rules. District councils may also find that they have designations or notices of requirement for such structures that need to be included in their plans.

The potential tools available for land-use planning to manage flood risks through RMA plans are outlined below. As a general rule, the level of control imposed through plans should be commensurate with the potential flood risk.  

 

Tool	Use and links to RMA plans	Level of control imposed
Identifying flood hazard through mapping and description of issues and scenarios	Generally used as an information tool that informs RMA plan provisions. It can either be part of a plan rule, or may dictate when plan provisions for managing flood risk apply. In other guises, it can be used to inform PIMs and LIMs.	Low when used as an information tool only. High when linked to plan rules.
Plan provisions that direct sensitive development away from areas of high flood risk (areas that experience frequent flooding and where there is a high potential for damage due to water level or water velocity)	Zoning land for less vulnerable land uses, such as 'open space recreational use', conservation, or hazard management. Such zoning may be linked to areas identified as being at most risk in mapping and scenarios. Provisions will generally exclude land uses such as commercial, residential, or industrial uses.	High
Rules that restrict the type of development that may occur	Often associated with hazard overlays linked to particular plan objectives, policies and rules. These work in a similar way to zoning, but do not replace the underlying zone. Plan rules restrict the type of development allowed to occur to those that are less vulnerable to flooding (e.g. grazing or recreational activities). Rules may also be written specifically to exclude activities that may obstruct flow paths (such as raised road embankments, concrete block walls, buildings, raised spectator facilities for sports grounds, or other barriers). Some regional plans also contain provisions relating to management of vegetation and structures in waterways that would otherwise clog or diminish the ability of a waterway to drain in a flood event.	Moderate to high
Development standards for activities located in flood prone areas.	Activities located in areas identified by zoning, overlays or other hazard mapping may be required to comply with objectives, policies and rules specifying: minimum floor or ground levels necessary to avoid a prescribed flood scenario (e.g. a 1% AEP event) restrictions on the ground coverage of any building or extension to an existing building minimum lot size or maximum building density controls (e.g. one building not exceeding 100 m2 per hectare) a requirement that buildings have 'sacrificial basements' or ground levels (areas under buildings that can be used for such things as garaging, but that are designed to ensure areas of the building vulnerable to flood damage are clear of anticipated water levels).	Low to moderate
Plan provisions concerning the establishment, ooperation, maintenance and protection of flood protection works.	Regional plan rules or consent conditions that: require the operation of flood protection works to be carried out in accordance with an approved management plan protect works such as stopbanks from unauthorised removal, partial removal, lowering, or undermining (including vehicle or stock access over or along a stopbank or other flood protection work) permit the use and repair of flood control structures on the beds of rivers and lakes provided that they have been legally established require resource consent applications for new structures or work that are located in a flood channel, bed of a river or lake to include an assessment of effects that includes consideration of impacts on existing flood protection works (such as increasing scouring, erosion, or decreasing flow rates) encourage the use of wetlands and restoration of natural channels where such action can avoid or mitigate flooding and erosion.	Moderate to high

 

Note that for district plans there are limitations in how effective land-use restrictions may be if existing use rights apply.

Councils should incorporate new flood risk-information into resource management plans as it comes to hand.  

 

Geothermal

Geothermal activity is generally restricted to a few locations around New Zealand.

Geothermal hazards include scalding hot water, geyser eruptions, geothermal chemicals in water (including sulphur), boiling mud, steam and other gases, geothermally altered ground (prone to subsidence and landslides), landslide, and hydrothermal eruptions.

Geothermal hazards are natural in origin and can be induced by human activity such as large-scale geothermal extraction activities. They can result in:

• changes in surface geothermal activity, including hydrothermal eruptions
• subsidence
• increased micro seismic activity
• effects on ecosystems, flora and fauna.

Regional and district plans should provide objectives, policies and methods for significant geothermal resources in their jurisdiction [if any]. Approaches to managing geothermal hazards include:

• scientific investigations to identify the scale, extent and nature of geothermal hazards, both when plans are developed or when consents are applied for in areas prone to geothermal hazards
• conditions on resource consents for geothermal extraction providing for specific monitoring of geothermal hazards. If monitoring establishes that there is a risk to life or property the resource consent should be reviewed under s128 of the RMA
• ensuring development avoids areas of high geothermal hazard risk
• where limited information is available, adopting a precautionary principle approach towards planning for activities in areas of actual or likely geothermal hazard risk
• re-injection of geothermal water in order to limit subsidence and land instability in geothermal areas
• requiring the provision of assessment of the effects of development on geothermal hazard risk in resource consent applications through RMA planning documents.

Local authorities should find a balance between the use of geothermal resources and protection from geothermal hazards in their policy responses.

When preparing plans, plan changes or variations local authorities should consider including assessment criteria for applications to use and develop geothermal resources to address geothermal hazards.

Meteorological

Meteorological hazards include weather-related events such as:

• flooding
• drought
• sea-level rise including storm surges
• extreme wind (including tornado)
• snow, frost, extreme temperature
• hail, lightning and fire (caused by lightning strike).

The effects of these hazards can be damage to infrastructure and property and the loss of life.

Modelling suggests climate change will increase the frequency and severity of such events to varying extents around New Zealand. The Ministry for the Environment has produced a guide to assist local government in planning for the effects of climate change: Preparing for Climate Change – A Guide for Local Government in New Zealand (PDF). NIWA has also produced a toolbox on the Impacts of Climate Change on Urban Infrastructure and the Built Environment.

Relatively few RMA plans currently contain provisions for meteorological hazards. In part this is largely due to the unpredictable nature of some of these events. However, a number of planning responses can be investigated for specific metrological hazards. Some aspects, such as building performance, are covered by the Building Code under the Building Act.

Issues and options that could be addressed through RMA plans could include:

• drought: the impact of drought is closely related to the availability and use of water. Objectives, policies, methods and rules in regional plans can be used to address the allocation of water resources. District plans can include rules requiring water storage for new subdivision and development.
• wind: district plans can include a requirement to mitigate the effects of wind on, or exacerbated by, new development
• fire can be caused by lightning strike. District plans can include fire setbacks for residential areas.

Outside the RMA, the Building Code and various standards provide some options for dealing with meteorological hazard risks.

The Building Act 2004 contains requirements for design to address issues associated with meteorological hazards. AS/NZS 1170 Structural Design Actions Set and 4203 General Structural Design and Design Loading for Buildings address earthquake forces, wind forces, snow loads, rainwater ponding loads, ice loads, soil loads and groundwater loads.

Tsunami

Tsunami are a series of large waves generated by sudden displacement of water (caused by earthquake, volcanic eruption or submarine landslide) capable of propagation over large distances and causing a destructive surge on reaching land. (The US National Oceanic and Atmospheric Organisation website has some useful material on tsunami).

Tsunami pose a risk to life, property and the environment by the inundation of water, which may also contain debris. Information on the risk to New Zealand and our level of preparedness is available via reports (compiled by GNS Science) on the Ministry of Civil Defence and Emergency Management website. The latest modeling was updated in mid-2013.

To date, few plans have addressed tsunami risks beyond general provisions and taking a precautionary approach. Councils should provide more direction by planning for the tsunami hazard and the management of its effects. This can be achieved by mapping areas susceptible to tsunami hazard and taking a precautionary approach in areas vulnerable to effects from tsunami.

The publication 'Designing for Tsunami: Seven principles for planning and designing for tsunami hazards' provides some concepts and ideas relevant to second-generation RMA plans based on United States experience. Key ideas that may be useful in a New Zealand context include:

• identifying areas that may be at risk of tsunamis and incorporating this information into short and long-term planning decisions. Incorporating information on tsunami risks into hazard registers can be used to help evaluate consent applications for major developments in coastal areas
• acquiring, designating or zoning areas at high risk from tsunamis for public open space use
• avoiding new development in identified or likely tsunami run-up areas. Development that may be directed away from such areas could include: residential, commercial, and industrial uses (especially those involving hazardous materials), and critical facilities and systems (communication, emergency response, electrical power, water supply, and natural gas systems)
• in areas where it is not feasible to restrict land to open-space uses, using other land-use planning measures. These include strategically controlling the type of development and uses allowed in hazard areas, and avoiding high-value and high-occupancy uses to the greatest degree possible. This approach could form the basis of objectives, policies and rules in RMA plans
• considering site-specific mitigation measures aimed at slowing, blocking, or redirecting water, or raising structures above the area of expected inundation. Such considerations could form the basis of resource consent conditions.

GNS has also produced guidance for integrating tsunami inundation modeling into land use planning(PDF).

Any land-use planning for tsunami needs to be integrated with a warning system and evacuation plan as, without these, many measures will not be effective. Good urban design can aid evacuation, such as the layout of roads and pathways (for example, ensuring there are roads that facilitate quick evacuation away from vulnerable areas by running perpendicular to areas such as beaches).

Overview of site-specific tsunami options

No one solution will fully address tsunami risk in all situations. Professional advice and design input should be sought when considering the following measures to reduce the risk of damage caused by a tsunami.

• Slowing techniques -
  These involve creating friction that reduces the destructive power of waves. Specially designed forests, ditches, slopes and berms can slow and strain debris from waves.
• Steering techniques
  These guide the force of tsunamis away from vulnerable structures and people by strategically spacing structures, using angled walls and ditches, and using paved surfaces that create a low-friction path for water to follow.
• Blocking
  Hardened structures such as walls, compacted terraces and berms, parking structures, and other rigid construction can block the force of waves. Blocking, however, may result in amplifying wave height in reflecting or in redirecting wave energy to other areas.
• Building design
  Where buildings are to be constructed in a tsunami hazard area, the design and construction of the buildings (including construction materials, building configuration and tsunami-specific design features), can reduce loss of life and property damage. Design and construction of new buildings should address forces associated with water pressure, buoyancy, currents and waves, debris impact, scour and fire. Substantially constructed buildings of concrete, masonry and heavy steel frames are likely to perform fairly well in a tsunami unless compromised by earthquake shaking. Wood-frame buildings, manufactured housing and light steel-frame structures at lower elevations close to the shoreline are likely to fare poorly in a tsunami.

Volcanic

Volcanic hazards include:

• lava flows
• ash fall
• gases
• lahars
• earthquakes
• debris avalanches (landslides)
• and pyroclastic flows.

These hazards are demonstrated in a diagram of volcanic features produced by the United States Geological Society. More information on the types and nature of volcanic hazards is available on the United States Geological Society website.

Pyroclastic flows can travel in excess of 15 kilometres from a volcano, and, depending on the wind, ash clouds can travel around the world from a single eruption.

Ashfall of 1 millimetre covers road markings, affects vehicle motors, water supply, wastewater, agriculture, horticulture, aircraft safety, electricity, buildings (for example, roof collapse) and communications. There are many areas in New Zealand where volcanic activity is now dormant, but may reoccur in the future.

To date, plan provisions addressing volcanic events and the management of the effects of this natural hazard have been limited to engineering solutions, emergency management planning, monitoring, and specific volcanic contingency plans. These plans are predominantly reactive, emergency management operational plans rather than specific land-use plans.

Councils should take a proactive approach to managing volcanic hazards through the inclusion of appropriate provisions in regional policy statements and plans (objectives, policies and methods) and encouraging good urban design. This could include:

• avoiding or restricting the location of facilities such as hospitals, schools, and other facilities that may be difficult to evacuate quickly in areas at risk from lahars, lava and pyroclastic flows, and debris avalanches
• requiring buildings in volcanic hazard areas to be designed and located in such a way that minimises risks (such as requiring strengthening of the roof and frame to withstand ash falls, or locating on higher ground away from likely mud or debris flow paths). These site-specific and activity-specific measures could be addressed through conditions on consents such as where design features to reduce risks from volcanic hazards are a matter of control or discretion. In Japan, buildings are designed to mitigate the effects of ashfall. This includes changes to roof design and stormwater collection from impervious surfaces
• designing safeguards for critical community networks (for example, water supply).

In Washington State (US) all counties are required to regulate land use and development within critical areas (for example, those defined as habitat and hazard).