Chapter 15 - Natural Hazards

Transcription

1 Chapter 15 - Natural Hazards 15.1 Introduction Natural hazards arise through the impact of natural occurrences on human life and property. The primary events that give rise to natural hazards within the district are events such as storms and the resulting flooding; snow and high winds; earthquakes and the associated damage from ground deformation, liquefaction, subsidence and earth shaking; climate change and the associated increase in sea level, and extreme weather events, which in turn can cause flooding, drought or an increase in wildfires. The negative effects of natural hazards can generally best be managed by avoiding development in areas which can be subject to natural hazards. However, it is recognised that all of the district, to a greater or lesser extent, can be subject to natural hazards. While avoidance may be the preferred option in many cases, in other situations mitigating the effects of natural hazards will be the only feasible option to ensure the health, safety and wellbeing of the district s residents Issues 1. Natural hazard events are difficult to predict and the magnitude of effects is uncertain. 2. When a natural hazard event occurs it can affect a large number of people. 3. The lifespan of built infrastructure and the memories of residents are often less than the expected return period of a natural hazard event. 4. The identification of new natural hazards can have unintended consequences including potential loss of property values or increased insurance premiums. 5. Avoiding the effects of natural hazards may not be possible and mitigating the effects can be costly. 6. The management of the effects of natural hazards can only occur when the hazard has been identified, and it is likely that not all natural hazards or areas affected by natural hazards, have been identified Objectives and Policies Objective 15.1 Subdivision, use and development of land is enabled while avoiding or mitigating the adverse effects of natural hazards. Policy 15.1 To avoid new subdivision, use and development of land in areas identified as subject to natural hazards 1. If the risk from the natural hazard is unacceptable, having taken into account the likelihood of the natural hazard event and the potential consequences for people, property, infrastructure and the environment, including the level of uncertainty about the likelihood or consequences; and 2. For high hazard areas, if the matters in Policy of the Canterbury Regional Policy Statement 2013 are not met. The negative effects of some natural hazards are difficult or costly to mitigate. Therefore in many situations, particularly in the rural environment, it is preferable to avoid subdivision, use or development in areas subject to natural hazards. In some cases mitigation works are a viable alternative to avoidance, particularly where the development is within a settlement (as defined in the Planning Maps) or where the natural hazard is Proposed Hurunui District Plan as Amended by Decisions 15 October

2 not likely to have significant effects on built infrastructure or people and communities health and safety. In these cases it may be appropriate to provide for additional subdivision use or development as long as the negative effects can be managed so that risks from the natural hazard are acceptable. Determining what level of risk is acceptable or not requires consideration of the likelihood of any natural event and its potential consequences, as well as considering the level of certainty about these two matters. Policy 15.1 of this section provides an overarching policy to guide the subdivision, use and development of land. This Policy is very similar to Policy within the Canterbury Regional Policy Statement and applies across all natural hazards. In any natural hazard areas that meet the definition of a high hazard area, the specific direction in the Policy Statement for these areas must be followed. While Policy 15.1 provides general direction, more specific policy guidance is provided for specific natural hazards below. Policy 15.2 To avoid development, excluding critical infrastructure, within areas at risk from flooding or ponding during a 0.5% AEP (Annual Exceedance Probability) storm event or within high hazard areas, unless: 1. an assessment is undertaken by a suitably qualified person which shows that the land is not subject to flooding or ponding during a 0.5% AEP storm event; or 2. appropriate mitigation measures are undertaken to mitigate the risk of flooding on property; and 3. the site is outside of a high hazard area; and 4. the development will not increase the risk to life and is of a type that is not likely to suffer material damage in an inundation event. Flooding during storm events is one of the most prevalent natural hazards within the district. It is only where flood waters are so high or so swift that travel becomes difficult or where flood waters enter dwellings, that the negative effects become significant. Predicting floodwater levels where the negative effects become significant is difficult, in part because the magnitude of extreme storm events is unknown and partly because modelling the likely flow paths of flood waters is costly and time consuming. Flooding high hazard areas are defined in the Canterbury Regional Policy Statement as flood hazard areas subject to inundation events where the water depth (metres) x velocity (metres per second) is greater than or equal to 1, or where depths are greater than 1 m, in a 0.2% AEP flood event. The District Plan identifies the major river flood plains. However, it is known that there are areas within these mapped flood plains which are unlikely to flood, and there are areas outside of the mapped areas which probably will flood in an extreme weather event. Policy 15.3 To avoid the subdivision, use or development of land within the Fault Avoidance Zone unless the adverse effects of fault rupture can be mitigated so as to ensure that there is no greater risk to health and safety during and after an earthquake. Policy 15.4 To avoid the development of land within any Fault Awareness Zones for post emergency infrastructure or infrastructure which large numbers of people congregate in, unless that infrastructure has been appropriately designed and sited in relation to the fault hazard. Proposed Hurunui District Plan as Amended by Decisions 15 October

3 New Zealand is geologically active, and the Hurunui District sits in the middle of the zone of geological activity. New Zealand s largest and most active fault, the Alpine Fault, runs parallel to the districts western boundary. The Hope Fault and its subsidiary, the Hanmer Fault, are the second most active faults in New Zealand. There are numerous other active faults and folds (a fold is where a fault does not reach the ground surface) which have been identified within the district, which have a longer recurrence interval and it is expected that there are other active faults within the district which are present but are as yet unidentified because their surface expression is masked by more recent geological activity. The Hope Fault and its subsidiary, the Hanmer Fault, have been modelled and mapping has been carried out on them within the Hanmer Springs and Mt Lyford villages. Other faults have been identified through a range of other studies, but the knowledge of the location and return interval of these faults is much less than that of the Hope and Hanmer Faults in Hanmer Springs and Mt Lyford. The framework in the District Plan recognises the difference in knowledge. Where detailed fault mapping has been undertaken the District Plan identifies these faults and a buffer zone around these faults as being a Fault Avoidance Zone. Subdivision, use and development within these Fault Avoidance Zones are restricted. It is expected that geotechnical analysis to identify the exact location of the fault trace would be required and any built infrastructure is designed and situated to ensure that it can withstand the damaging effects of earth shaking. For other faults identified within the District Plan, where detailed geotechnical analysis has not been undertaken, a Fault Awareness Zone has been included within the District Plan. Because the knowledge of these faults is not as comprehensive, and the exact location of the fault or fold is unknown, a larger buffer zone has been applied. Building within the Fault Awareness Zone is a permitted activity. However, geotechnical analysis is expected at the time of subdivision or plan change. Policy 15.5 To avoid the subdivision of land in a Liquefaction Awareness Zone unless a geotechnical investigation is undertaken, the risk of liquefaction is determined, and if necessary appropriate mitigation, including foundation design and land stability engineering is undertaken. Policy 15.6 Mitigation works to minimise the effects of natural hazards shall be undertaken in a way which avoids, remedies or mitigates adverse effects on cultural, social and environmental values and the health and safety of communities. Policy 15.7 To avoid the subdivision, use or development of land within the seaward side of the Coastal Hazard Line unless the proposed development is the repair or upgrade of existing infrastructure; and mitigation is undertaken to ensure that there is no increased risk to life or built infrastructure or a consent has been sought and granted for the proposed development under the Regional Coastal Plan. The Canterbury Regional Council manages activities within the Coastal Hazard Area. However, the Regional Council does not have the ability to control subdivision under the RMA. The Council recognizes that, in limited situations, there may need to be additional subdivision, within this area. Where the subdivision of land within the seaward side of the Coastal Hazard is required to repair or upgrade existing infrastructure, the Council may consider this development appropriate. However, in Proposed Hurunui District Plan as Amended by Decisions 15 October

4 most cases, unless consent has been applied for and granted by the Canterbury Regional Council additional subdivision will not be appropriate within this area. Policy 15.8 To recognise that climate change could alter the frequency and duration of some natural hazard events. Any mitigation works should take into consideration the need to be precautionary given the uncertainties as to the magnitude of effects from climate change. New subdivision, use and development should consider the consequences of a mean sea-level rise of at least 0.8m relative to the average. The majority of the international science community now agrees that global climate change is occurring. However, there is still uncertainty as to the magnitude of the future effects of this climate change and the extent to which human activities are causing this change in the global climate system. Despite this uncertainty the Council recognises that climate change can exacerbate some natural hazards like flooding and sea water inundation, therefore mitigation measures that are developed are constructed in such a way that they take into account the likely effects of this change. Policy 15.9 To assess the risks of natural hazards prior to land being rezoned and to avoid or mitigate those risks. The Council s knowledge of the natural hazards that may affect the district is not perfect. It is recognised that the most in-depth studies have occurred within the area s which are already zoned for urban purposes. Prior to any new land being rezoned a full assessment of natural hazard risks should be undertaken and any mitigation works which are required are included within the District Plan. It is generally expected that any mitigation required will be constructed prior to the construction of any other built infrastructure, particularly dwellings. Policy To ensure that new subdivision within the Mt Lyford area appropriately addresses the risk of uncontrolled wildfire to provide for residents and visitors health and safety. Mt Lyford village is a unique area within the district. The Mt Lyford area is based on buildings being of log construction. The Mt Lyford area also has significant areas of native vegetation close to dwelling sites. Firefighting capability in the area is also limited. Policy To recognise that the risk of flooding can be reduced by mineral extraction activities in river beds that increases their flood carrying capacity Rules General Rules 1. Determining activity status where the same matter is controlled by more than one rule: (a) the user must firstly review the activity status of the activity and its associated controls within the zone or district-wide provisions applying to the site; then (b) taking the activity status resulting from clause (a) above, the user must then review any overlays that apply to the site. If an overlay rule applies to the same matter then the most restrictive activity status will apply; and Proposed Hurunui District Plan as Amended by Decisions 15 October

5 2. The rules in Chapter 15 do not apply to land use between the Coastal Hazard Line (as detailed on the District Plan maps) and the Coastal Marine Area which are managed under the Regional Coastal Plan. The Canterbury Regional Council s functions do not include the control of subdivision. Therefore, while the management of the effects of coastal hazard arising from the use and development of land (and vice versa) to the seaward side of the Coastal Hazard Line is achieved through the Regional Coastal Environment Plan, the management of subdivision is controlled by this Plan (see Chapter 5 Subdivision) Permitted activities 1. The following activities are permitted activities: (a) Any activity within a Natural Hazard Area or a Natural Hazard Assessment and Awareness Area that complies with the standards in Rule Note 1. The control of the use and development of land to avoid or mitigate coastal hazard on the seaward side of the Coastal Hazard Line is achieved through the provisions of the Regional Coastal Environment Plan. Any land use in this area must comply with the provisions of that Plan and may require resource consent approval from the Canterbury Regional Council. Refer to Policy Note 2. Refer to the Planning Maps and Appendix 15.1 Schedule of Natural Hazard Areas and Appendix Schedule of Natural Hazard Assessment and Awareness Areas. (b) Building on sites within the Residential (River Edge) or Woodbank (River Edge) Zone in Hanmer Springs following: (i) the provision to the Council of written confirmation that the flood protection work authorised by the Canterbury Regional Council in Consent Number CRC has been completed along the Chatterton River boundary to the Residential (River Edge) Zone to the satisfaction of the Canterbury Regional Council; and (ii) the provision to the Council of written confirmation that the stopbank between the Chatterton River and the western boundary of this zone has been upgraded to be 600 mm above the level required to provide protection from a 0.2% AEP (1 in 500 year) flood event Standards for permitted activities 1. The following standards apply to activities within a Natural Hazard Area identified in the planning maps and in Appendix 15.1: (a) In areas listed in Appendix 15.1 Schedule of Natural Hazard Areas, there is to be no siting, erection, replacement of, or extension to, any building or structure except for: (i) community amenity facilities; or (ii) fencing; or (iii) farm accessory buildings (not including those containing any intensive farming) and nonhabitable residential accessory buildings; or (iv) normal maintenance, including repairs, which does not alter the character, footprint, intensity or scale of the existing building or structure; or (v) those activities specified in (c), (d) and (e) below; and (b) There is to be no trimming or removal of trees in Land Instability Areas except for maintenance and pruning limited to: (i) living branches that have a diameter of 50 mm or less, or are within 2 m of the outermost foliage; or (ii) any dead wood; or (iii) activities in accordance with an approved reserve management plan; or (iv) works required by the Electricity (Hazards from Trees) Regulations (c) For dwellings, extensions to dwellings, habitable accessory buildings or principal buildings located within the Fault Avoidance Zone, the location, design and construction complies with the recommendations of an organisation or individual that has been authorised by the Chief Executive of Hurunui District Council as being appropriately qualified and experienced; and Proposed Hurunui District Plan as Amended by Decisions 15 October

6 (d) Buildings on sites in the Woodbank (River Edge) Zone in Hanmer Springs are to have a minimum floor height of mrl; and (e) For activities located within the Coastal Hazard Zone, the activity is a permitted activity under any relevant Regional Plan or a resource consent for the activity has been granted by the Canterbury Regional Council. 2. The following standards apply to activities within a Natural Hazard Assessment and Awareness Areas identified in the planning maps and in Appendix 15.2: (a) For dwellings, extensions to dwellings that increase the floor area by no more than 10% from that existing at 15 October 2016, habitable accessory buildings or principal buildings located within the Flood Assessment Zone, a floor level is provided which is at least 400 mm above the 0.5% annual exceedance probability (1 in 200 year event) flood event. Compliance with this standard shall be demonstrated by a flood assessment from an organisation or individual that has been certified by the Chief Executive of Hurunui District Council as being appropriately qualified and experienced; (b) For buildings or structures located within a Fault Awareness Zone, the building or structure is not a Building of Importance. Note: The Canterbury Regional Council is authorised under Rule 15.3(2)(a) to provide advice on what a likely water level is during a 0.5% annual exceedance probability flood event Discretionary activities 1. Any activity that does not meet any one or more of the standards for permitted activities in Rule and is not classified as a non-complying activity under Rule Non-complying activities 1. The following activities are non-complying activities: (a) A Building of Importance located within a Fault Avoidance Zone Assessment Criteria When considering an application and whether or not it can be granted pursuant to Part 2 of the RMA, the Council will have regard to the relevant assessment criteria: 1. The probability and possible magnitude of the event; 2. The type, scale and distribution of any potential effects of the hazards; 3. The nature of the activity and the degree to which it may increase the potential risk to human life, property or the environment; 4. Any recommendations from a qualified professional such as a specialist engineering geologist or geotechnical engineer; 5. The outcome of any consultation with the Canterbury Regional Council and any recommendations resulting from that consultation; 6. The extent to which a proposed development meets the objective, functional requirement and performance provisions of the New Zealand Building Code; and 7. Anticipated natural hazard damage and costs and the estimated benefits to the community of the proposed development. (Costs and benefits to take into account both monetary and nonmonetary costs and benefits). Proposed Hurunui District Plan as Amended by Decisions 15 October

7 Appendix 15.1 Schedule of Natural Hazard Areas Natural Hazard Areas Coastal Hazard Area Coastal erosion: Coastal Hazard Line Planning maps B,E,G,K,M,N,2,3,4,5,9,10,16 Note: Coastal Hazard Lines 1 and 2 established by the Canterbury Regional Council as part of its Regional Coastal Environment Plan have been incorporated into the District Plan in order to integrate the management of coastal hazards. The Regional Council Coastal Hazard Lines cover land which is at risk from coastal erosion within the next 50 (line 1) and 100 (line 2) years. The Coastal Hazard Line detailed on the District Plan maps shows the most landward of these two lines. Any land use on the seaward side of the Coastal Hazard Line shown on District Plan maps must comply with the provisions of Regional Council Environment Plan. Refer to Policy 15.8 and the associated methods. Earthquake hazards Fault Avoidance Zones Fault lines: Hanmer fault, Hanmer Springs Hope Fault, Mt Lyford Planning maps I,Ia,Ib,6,7,18 Planning maps O,17 Note: Including an area 20 m wide on either side of the fault lines identified on the planning maps Land Instability Areas Slope Hazards: Slope hazard areas 3 and 4 Hanmer Springs Planning map Ib Proposed Hurunui District Plan as Amended by Decisions 15 October

8 Appendix 15.2 Schedule of Natural Hazard Assessment and Awareness Areas Flood Assessment Zones Rivers: Blythe River Chatterton River Hanmer River Waitohi River Pahau River Conway River Hurunui River Mason River Jed River Motunau River Waiau River Kowai River Planning maps 4, 10 Planning maps I, 6 Planning maps 6, 7, 15 Planning maps 11 Planning maps 10, 11, 14, 15 Planning maps 16 Planning maps 10, 11 Planning maps Q, 15 Planning maps D, 5, 10 Planning maps 3, 9 Planning maps P, Q, 5, 6, 7, 14, 15, 16 Planning maps A, B, L, M, S, 1, 2, 9 Ponding: Amberley Beach Leithfield Beach Hawarden Planning maps 2, B Planning maps 2, M Planning maps J Note: The coastal area from Amberley Rocks to the southern boundary of the district is in the Flood Assessment Zone due to a combination of flooding from the Kowai and Waipara River mouths, low lying land, run off from Hursley Terrace to the east and sea water inundation. As such the potential flooding is not from one single source. Fault Awareness Zones Fault lines: Awatere fault Island Pass fault Fowlers fault Clarence fault Elliot fault Hope fault Hanmer fault Kakapo fault Poulter fault Planning maps 19, 20 Planning maps 20 Planning maps 18, 19, 20 Planning maps 7, 13,14,18,19 Planning maps 18 Planning maps I, O, 6, 7, 13, 14, 15, 17, 18 Planning maps I, Ia, Ib,6, 7, 18 Planning maps 7, 13, 14 Planning maps 12, 13 Proposed Hurunui District Plan as Amended by Decisions 15 October

9 Mt Leslie fault Lottery River fault Mason River fault Conway - Charwell faults Oronoko fault Esk fault Hurunui Peak fault zone Balmoral fault Mt Culverden fault Red Post fault The Humps fault Leonard Mound fault Lowry Peaks fault Hurunui Bluff fault Virginia fault Heathstock fault Masons Flat fault Horsley Down fault Medbury faults Trig C faults Mt Alexander fault Moores Hill fault Kaiwara fault Leamington faults Royal Stream fault Hundalee fault Lees Valley fault Birdseye fault Karetu fault Birch fault Doctors anticline Boby Stream fault Coastal fault-fold belt Amberley fault Seadown anticline Kate anticline Mound anticline Omihi fault Hamilton fault Monserrat anticline Planning maps 6, 7, 15 Planning maps O, 15, 17,18 Planning maps O, 17 Planning maps 17 Planning maps 12 Planning maps 11, 12 Planning maps 11, 14 Planning maps 11, 14 Planning maps 14, 15 Planning maps 15 Planning maps 15, 16 Planning maps F, 10, 15 Planning maps 10, 15 Planning maps 10, 11 Planning maps 11 Planning maps 11 Planning maps 9, 11 Planning maps J, 9, 11 Planning maps 11 Planning maps 9, 11 Planning maps 10 Planning maps R, 9, 10, 11 Planning maps 9, 10, 16 Planning maps 5, 16 Planning maps 16 Planning maps 16 Planning maps 8 Planning maps 8 Planning maps 8, 9, 11 Planning maps 8, 9 Planning maps 2, 3, 4, 5, 9, 16 Planning maps 2, 9 Planning maps A, 2, 9 Planning maps 9 Planning maps S, 9 Planning maps 9, 10 Planning maps 9 Planning maps 3, 9, 10 Proposed Hurunui District Plan as Amended by Decisions 15 October

10 Motunau faults Happy Valley fault Greta Valley fault Blythe fault Stonyhurst syncline Lower Hurunui faults Mt Seddon anticline Hawkswood anticline Planning maps 3, 9 Planning maps N, 3, 10 Planning maps H, 9, 10 Planning maps 3, 4, 10 Planning maps 3, 4, 10 Planning maps 4, 10 Planning maps G, K, 3, 4, 5, 10 Planning maps G, 5, 16 Note: Including an area 250 m wide on either side of the fault lines identified on the planning maps Liquefaction Assessment Zone Liquefaction Assessment Zone Planning maps B, L, M, 2, 9 Note: For rules related to the Fault Awareness Zone and Liquefaction Assessment Zone refer to Chapter 5 Subdivision. Proposed Hurunui District Plan as Amended by Decisions 15 October