11. Natural Hazards Volume One [R, D] Policy 11.1.16 – Refine the boundaries of flood hazard overlays in response to: (a) changes to levels of protection provided by flood defences and other flood mitigation/management works; or (b) new observations of flood events or more detailed assessment of the flood hazard; or (c) changes in catchment hydrology due to land use change or climate change; or (d) changes in flood hydraulics due to channel aggradation or erosion, vegetation growth within the floodway or sea level rise. The mapped flood risk will change from time to time either because the flood risk physically changes or because the Council’s knowledge of flood risk improves with more information and/or analysis. Where the extent of the flood hazard changes as a result of the matters set out in (a) to (d), it will be necessary to refine the boundaries of the flood hazard overlay in the MEP. This refinement is likely to occur on an ongoing basis. Any such changes will have to pass through the First Schedule process of the RMA. Earthquake and liquefaction [D] Policy 11.1.17 – Avoid locating residential, commercial or industrial developments on Rural Environment or Rural Living zoned land on the Wairau Plain east of State Highway 1/Redwood Street, unless remediation methods are to be used to reduce the level of liquefaction risk to an acceptable level. Liquefaction is the process by which earthquake shaking causes increased pore water pressure in soils that in turn reduces the strength of the soils. The potential for shaking intensities sufficient to trigger liquefaction is significant given the overall seismicity of the District. Land underlain by the “Dillons Point Formation” on the Wairau Plain has an elevated risk of liquefaction. The Dillons Point formation is marine sediment deposited on the eastern margin of the Plain by previous marine processes and consists of grains of small and relatively uniform particle size. These characteristics, combined with high groundwater levels, are conducive to liquefaction. The western extent of the Dillons Point formation (at a thickness that represents a significant liquefaction risk) is approximately State Highway 1 and Redwood Street. This policy signals that it would be unwise to allow any future commercial, industrial or multi-lot residential developments to occur on rurally zoned land underlain by the Dillons Point formation due to the high risk of liquefaction. Such liquefaction has the potential to cause significant damage to buildings and infrastructure and would therefore cause significant disruption to residential, commercial or industrial activity. A policy of avoiding such development of land ensures that significant investments and community infrastructure is not subject to unnecessary risk. In some situations, it may be possible to implement remediation methods to reduce the level of risk to an acceptable level. This will be assessed on a case-by-case basis. This policy applies to the rezoning of land that would facilitate these developments or to resource consent applications for subdivision or development. In the case of resource consent applications for residential subdivision and development, the threshold for the application of the policy is the creation or development of lots smaller than one hectare. The density of development where lots are in excess of one hectare is considered an acceptable risk given the probability of an earthquake occurring. 11 – 8