11. Natural Hazards Volume One (c) avoiding houses and other habitable structures in locations where they will be subject to a Level 3 flood risk. Given the potential consequences of a person choosing to reside in a flood prone area, it is considered appropriate to exercise control over any such proposal. This will enable the Council to reduce the risk to life and property from flooding. The matters in (a) to (c) identify how that risk reduction will occur given the likely severity of any flooding event. Minimum floor levels will be sufficient where land is subject to Level 1 flood risk, as this will mitigate any adverse effects by ensuring any house or other habitable structure is above flood waters and that people can still safely reside in the house/structure during and immediately after a flood event. The appropriate minimum floor level will be determined through the building consent process and in many cases a floor level of 450 mm above the natural ground level will be sufficient. Where the flood hazard is not well understood (i.e. Level 2 flood risk), it is appropriate that a precautionary approach is taken and that the flood hazard is evaluated. The results of this evaluation may trigger other policies in this chapter. It is not appropriate to allow people to reside on land subject to a Level 3 flood risk, as the deep and fast flowing water would present an unacceptable risk to life and property. [D] Policy 11.1.11 – Avoid locating intensive residential, commercial or industrial developments on land subject to a Level 4 flood risk. It is possible that areas protected by flood defences will experience extraordinary flood events that exceed the annual recurrence intervals specified in Policy 11.1.4 and subsequently overwhelm stop banks or other flood defences. In some areas, this will result in a sudden occurrence of deep, fast flowing waters that could endanger life, property and regionally significant infrastructure. Although such an event has a very low probability of occurring in any given year, the adverse effects could be catastrophic if intensive development is allowed to occur in these areas. The Council has considered this and has signalled through this policy that it would be inappropriate to allow any future commercial, industrial or multi-lot residential developments to occur in areas subject to a Level 4 flood risk. 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 less than one hectare. The density of development where lots are in excess of one hectare is considered an acceptable risk given the probability of flood breakout occurring. [D] Policy 11.1.12 – Where an activity within an area subject to a flood hazard overlay is dependent upon the provision of flood defences to reduce the risk of flooding, there must be an ongoing commitment to the maintenance of the flood defences over time. The provision of flood defences (either new or existing) may be sufficient to reduce the risk of flooding of any proposed development. The protection afforded by the flood defence (whether public or private) will only be provided if it is maintained on an ongoing basis. For example, stopbanks can erode and vegetation can compromise the efficiency of a floodway or the integrity of a stopbank. If resource consent is to be granted for a development within an area subject to a flood hazard overlay and that resource consent is dependent on a flood defence, then a requirement for the private flood defence to be maintained should be imposed. The Council is only likely to undertake maintenance of privately constructed flood defences where they directly adjoin and integrate with existing Council administered defences. In other situations, the obligation for maintenance will be that of the consent holder. 11 – 6