Volume One 11. Natural Hazards [D] Policy 11.1.18 – Where it is proposed to subdivide land zoned Urban Residential 2 – Greenfields and land identified in Appendix 23 for residential purposes, the subsoil of the site must be investigated to establish if specific foundation designs of buildings are required to mitigate the effects of liquefaction or lateral spread. There are areas of land zoned for residential development that may have localised soils susceptible to liquefaction and/or lateral spread. The policy requires that, in the event of proposals to subdivide land within the Urban Residential 2 – Greenfields Zone and within the land identified in Appendix 23 for residential development, that the subsoil be specifically investigated to establish the risk of these hazards occurring in the event of an earthquake. For land zoned Urban Residential 2 – Greenfields, standards set out the nature of those investigations. The results of the investigation will determine whether specific foundation design will be required to mitigate the effects of liquefaction and/or lateral spread. Land instability [D] Policy 11.1.19 – Control the erection and placement of structures within areas prone to tunnel gully erosion. The extent of land potentially subject to tunnel gully erosion in Marlborough and the nature of the resulting hazard are well understood. The hazard is directly linked to loess soils that exist predominantly in the hill country along the southern boundary of the Wairau Plain. The Council (and its predecessor) has a long history of managing the risk of tunnel gully erosion. In areas prone to tunnel gully erosion, it is important that any new structure is not subject to an unreasonable risk of damage. The controls will be primarily applied through the Building Act 2004. The policy allows, in conjunction with Policy 11.1.20, the risks to life and property created by unstable ground to be reduced. Areas of loess soil are identified in the MEP. [RPS, R, D] Policy 11.1.20 – Continue to manage the Wither Hills Soil Conservation Reserve to maintain and enhance soil stability. The Wither Hills Soil Conservation Reserve comprises 1,100 hectares of land the length of the southern boundary of the Blenheim urban area. The soils over the Reserve are loess and are particularly vulnerable to tunnel gully erosion. Eroded material has the potential to fill stream channels at the base of the Wither Hills and create a flood risk for the Blenheim urban area. This policy signals that soil conservation management will continue for the foreseeable future to manage this flood hazard. This will be achieved through an active programme aimed at maintaining and enhancing soil stability over the Reserve. [D] Policy 11.1.21 – Locate new structures and works to: (a) avoid them being damaged from the adverse effects of land instability; and (b) avoid any increase in the adverse effects of slope instability that the structure or work may cause. Marlborough is characterised by steep terrain and in some locations, unstable geology. Combined with the potential for intense rainfall events, these factors create the potential for slope instability. Examples historically include rock/debris slumps, debris slides or flows, coastal erosion and tunnel gully erosion in various parts of the District. Establishing residential, commercial or industrial development or infrastructure supporting that development or linking our communities in locations prone to land instability will lead to unsustainable outcomes. This policy requires new structures and works to be located in environments that avoid adverse effects caused by land instability. It also addresses the situation of a structure or work exacerbating 11 – 9