3l NATURAL HAZARDS AND UNSTABLE GROUND

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1 Page 1 of Section 3l 3l NATURAL HAZARDS AND UNSTABLE GROUND 3l.1 Introduction A natural hazard is the result of natural processes that form, shape and change the environment and interact or potentially conflict with human activities. Land use activities need to be carefully managed to avoid or mitigate any potentially adverse effects from natural hazards. It may be difficult to avoid adverse effects in already developed areas, but measures may be required to ensure the effect of the natural hazard is not increased or the risk to the community intensified. Taupō lies in an area subject to a number of different natural hazards and there are specific areas of the District which are particularly vulnerable to the effects of natural hazards. The risk to property can sometimes be reduced or avoided by locating a reasonable distance from known hazard areas, and in some circumstances by adopting specific design techniques. The Plan controls development in areas where there is an identified risk from a natural hazard. Where it is not possible to avoid or mitigate the risk, activities may not be appropriate in these locations. Procedures also exist outside the Plan, which can help the community prepare, plan, and respond on an individual and District level to the after effects of natural hazard events. The Resource Management Act 1991 (the Act) gives responsibilities for the control of the use of land for the purposes of the avoidance and mitigation of natural hazards to both regional and territorial authorities. The Regional Policy Statement states how the different roles and responsibilities of the different authorities in relation to natural hazards will be undertaken. This document states that territorial authorities have historically undertaken the function of controlling land for the avoidance or mitigation of natural hazards and until a new division of responsibility is determined by agreement, this situation will continue. i. LAND INSTABILITY An area historically affected by landslides is Waihi on the southern edge of Lake Taupō. Landslides in this area have resulted from the failure of hydrothermally altered rock in the thermally active area of the fault scarp. Landslides have in the past caused extensive property damage and loss of life. The potential for damage to property from a landslide in this area is high. Areas of jointed rock and cliffs can be affected by ground shaking, forming rock topple areas. A number of rock topple areas exist within the District such as Motuoapa and Waihi. Tomos are a form of subsurface erosion which occur in permeable soils such as tephra and pumice. The movement of groundwater can result in the formation of voids and channels below the surface creating pipes. The collapse of these pipes cause ground subsidence. Areas particularly susceptible to the formation of tomos are areas above the water table close to steep slopes or gullies, which allow ground water to discharge rapidly. The moving nature of tomos makes it difficult to pinpoint the exact location of these hazards. Therefore, there is a need to be aware of the tomo hazard although specific controls are not proposed through the District Plan to address this phenomenon. Uncompacted fill can cause land instability and subsidence resulting in damage to buildings and infrastructure. Sawmills were a feature of the Taupō landscape over the last century and many gully systems within what is now Taupō town provided ideal locations for the dumping of waste material from these milling operations. Waste material such as sawdust does not consolidate and eventually rots causing subsidence. The exact location of these dumping sites is unknown and therefore specific controls are not proposed through the Plan to address this hazard. FLOODING Inundation can occur as the result of water flowing over the top of riverbanks and flooding adjoining land; the capacity of a lake being exceeded and flooding lakeshore properties; and of properties being located in ephemeral waterways. The Waikato and Tongariro Rivers, along with other smaller river systems, for example, the Kinloch, Waitahanui, Hinemaiaia,

2 Page 2 of Section 3l Tauranga-Taupō, Waimarino, Waiotaka, Tokaanu and Kuratau Rivers can be affected by flooding. In some areas mitigation measures such as stopbanks exist and allow the use and occupancy of the flood plane at an acceptable level of risk. However, activities need to recognise that there is still a hazard when the capacity of the stopbanks is exceeded. i EROSION Lakeshore erosion can occur as the level of a lake rises and falls. In addition the location of structures in and around the lakeshore edge can contribute to and increase the erosion hazard. Erosion of riverbanks can occur as a result of a flood event or the on-going change of a river system. While the erosion risk can alter over time there are some areas of development within the District currently at risk from riverbank erosion, notably on the Tongariro River. THERMAL AREAS Thermal areas have the potential to cause subsidence and can create a number of hazards including subsidence, hot ground and hydrothermal eruptions. Thermal areas can be difficult to define as the boundaries and extent of areas of hot ground can change over time. These thermal areas occur in a number of locations around the District in both rural and urban areas. v. EARTHQUAKES Active faulting is common within the District and there are many known fault lines. Movement along fault lines can cause ground rupture or deformation. The severest effects of fault line movement can be avoided or mitigated by locating structures and buildings away from known fault lines or, in some circumstances, undertaking specialist structural, design or building techniques. The degree to which an area will experience ground shaking (amplification), as a result of earthquakes will depend on the type of ground materials present in that area. Low-density pumiceous material, which makes up the majority of the District, partially absorbs the energy created by the movement of the earthquake. This results in lower than expected shaking intensities. In low-lying swampy alluvial areas with soft flexible sediments, such as Motuoapa, Turangi and Rotoaira, amplification of ground movement will be intensified. vi. VOLCANIC HAZARDS Lake Taupō occupies the caldera of an active rhyolitic volcano. An eruption from the Taupō Volcanic Zone (which includes the volcanoes Ruapehu, Ngauruhoe and Tongariro, is a major threat (but of low probability) to the economy and population of the Taupō District. Ash fall from volcanic eruptions has the potential to affect a large portion of the District. Volcanic ash is abrasive, mildly corrosive and potentially conductive when wet. The impacts of ash fall will generally be disruptive rather than destructive, primarily affecting the function of infrastructure and services around the District. It is not possible to avoid the effects of ash fall on the District, however mitigative measures will either prevent or limit ash entering systems or provide for the efficient removal of ash. It is important to ensure essential services are maintained and that people are aware of the risk and the ways in which they can mitigate that risk. In rural areas and other locations where connection to a central water supply is not provided, protecting individual water supplies from ash fall will enable people to respond and recover from the effects of the hazard sooner. Lahars have the potential to affect the river valleys around Ruapehu, Ngauruhoe and Tongariro. Lahars will destroy infrastructure and buildings in their path as well as having a continuing impact on river systems, water quality and flooding. Areas around Turangi are vulnerable from lahars down the Tongariro River system. Civil Defence teams and other emergency services must deal with the effects of lahars should this hazard occur.

3 Page 3 of Section 3l 3l.2 Objectives and Policies OBJECTIVE 3l.2.1 POLICIES Protection of activities, development and life from the adverse effects of natural hazards. i. Control the design and location of activities and development within identified natural hazard areas, or areas which have significant potential to be affected by a natural hazard, to avoid or mitigate the effects of the natural hazard. Manage the location, design, and type of new activities and development to avoid or mitigate the adverse effects of flooding, erosion, ground rupture and deformation, hot ground and land instability on development and the community. EXPLANATION In the past, development has occurred in areas subject to the effects of natural hazards. This has required development of structural protection works to protect the investment made by the community and individuals in these areas. By controlling the location or type of development in areas subject to natural hazards, the loss suffered by the community and the financial burden of response and recovery from natural hazard events can be reduced. The District is subject to the effects of a range of natural hazards. Studies have identified a number of areas where the risk from natural hazards is high. The Plan has identified a number of areas where the effects of natural hazards can be avoided or mitigated through land use controls. In these areas development will be managed and controlled through rules and performance standards to reduce or minimise the risk to individuals and the community. Other areas at risk from natural hazards, which are known to the Council, have been identified on a Natural Hazards Register. The information on the Natural Hazards Register is not included in the Plan but is provided to help people make informed decisions about land and development in the District. Measures undertaken to avoid or mitigate the effects of natural hazard need to be assessed through a resource consent application. Assessment can ensure residual risk to the community and the risk to adjoining properties is minimised and also make certain appropriate measures are taken to confirm existing and future owners are aware of and accept the risk of the natural hazard. OBJECTIVE 3l.2.2 POLICIES Activities and development do not create, accelerate, displace, or increase the effects of a natural hazard. i. Ensure that activities do not alter or change the nature of a natural hazard event, increase the intensity of a natural hazard event or increase the risk of the event occurring. i Ensure that activities and structures do not increase the risk to the community or the environment from the effects of natural hazards. Ensure that where development occurs within areas subject to the effects of natural hazards, property owners and/or occupiers are informed of and manage the risk. Control the location and presence of hazardous substances in areas subject to natural hazards to ensure that there is no increase in the effects of the natural hazard or risk to the community from hazardous substances.

4 Page 4 of Section 3l EXPLANATION Activities and land uses can increase the severity of a natural hazard, alter the effects of a natural hazard, or cause the hazard to affect previously unaffected areas. Proposed activities and development including earthworks within hazard areas should not alter the nature, scale, or intensity of the hazard or pass the risk onto other sections of the community. The effects of natural hazards can be caused, accelerated, displaced, or increased by certain activities. The location of structures within hazard areas has the potential to increase the risk to other sites. Earthworks may alter the direction and intensity of a flood event by diverting floodwaters or altering drainage functions, while the presence of hazardous facilities or substances within areas subject to natural hazards may cause additional potential adverse effects from a hazard event. Measures to ensure that there is no increase in risk as a result of land use activities within natural hazard areas need to be adopted. The Plan has only identified Natural Hazard Areas where it is possible for the effects of those natural hazards to be avoided or mitigated though land use or regulatory controls. Other natural hazards exist in the District but are unable to be avoided or mitigated through the provisions of the Plan. 3l.3 Methods i. Performance standards for permitted activities within identified natural hazard areas. i Environmental assessment of activities which do not comply with performance standards through the resource consent process. Conditions on resource consents such a minimum floor levels in identified flood prone areas. Identify areas subject to the effects of Natural Hazards (Hazard Areas) in the District Plan, where activities will be controlled or restricted by rules. v. Maintain a Natural Hazards Register (held outside the Plan) to inform people about the range and extent of natural hazards which affect the District. vi. v vi ix. Civil Defence and Emergency Management Plans for response and recovery from hazard events (at a National, Regional and District level) under the Civil Defence Act Education and information of the risks associated with natural hazards Allocation of resources through the Strategic and Annual Plan processes where measures to avoid, mitigate or remedy the effects of natural hazards in public areas, is appropriate. Section 106 of the Resource Management Act 1991 to control the subdivision of land subject to a natural hazard. x. Land Information Memorandum (LIM) process under the Local Government Act 1974 to inform landowners about natural hazards which the Council is aware of on individual properties. xi. x xi Project Information Memorandum (PIM) process under the Building Act 1991 to inform landowners of potential and identified natural hazards areas. Structural works to avoid the effects of natural hazards where deemed appropriate and necessary. Section 36 of the Building Act 1991 to control the inappropriate development of land subject to a natural hazard. x Policy and rules within any Regional Plan or Policy Statement in relation to natural hazards.

5 Page 5 of Section 3l xv. Further study into the Flood Hazard Areas to ensure that the information held within the Plan is up to date. xvi. The implementation of any Joint Management Agreement between Council and Iwi. 3l.4 Principal Reasons for Adoption It is important to identify areas which are affected by natural hazards to ensure risks to people, development and the environment are avoided or mitigated through appropriate management techniques. Identifying hazard areas in which rules and performance standards manage levels of activity enables decisions to be made about the use and development of land which takes into consideration the level of risk and nature of the natural hazard. Natural hazards are unpredictable and it is not always possible to avoid or mitigate the effects of all natural hazards. Where information is inaccurate or uncertain, rules and performance standards may not always be the appropriate tool. In these circumstances non-regulatory tools such as the Natural Hazards Register, Emergency Management Plans and response strategies are more suitable. 3l.5 Anticipated Environmental Outcomes i. Activities or structures do not create, accelerate, displace, or increase the effects of a natural hazard. i Reduction of risks to the community from natural hazards. Greater public awareness of natural hazards and their potential effects on people and development within the District.