Volume One 11. Natural Hazards Flooding – management of activities in flood prone areas [D] Policy 11.1.8 – Unless provided for by Policy 11.1.10(a), avoid locating houses and other habitable structures, including associated on-site wastewater management systems, where they could be inundated or otherwise damaged by flood events. The policy directs that to avoid or mitigate the adverse effects of flooding, any house or other habitable structure should be free from inundation. It also recognises that the servicing of the house in terms of domestic wastewater is important in terms of avoiding material damage to properties. The exception recognises that Policy 11.1.10(a) provides a means of mitigating the adverse effects of flooding by establishing minimum floor levels. [R, D] Policy 11.1.9 – Establish a hierarchy of flood risk as follows: (a) Level 1: Land that suffers flooding of shallow, low velocity water in a flood event with an annual recurrence interval of 1 in 50 years; (b) Level 2: Land that suffers flooding but the depth/velocity of the flooding is not well understood, or cannot easily be expressed relative to natural ground level, in a flood event with an annual recurrence interval of 1 in 50 years, or land within 8 metres of any lake, river or wetland; (c) Level 3: Land that suffers flooding of deep, fast flowing water in a flood event with an annual recurrence interval of 1 in 50 years, or land in the bed of any lake or river or in any wetland; and (d) Level 4: Land that has the potential to suffer flooding of deep, fast flowing water in an extreme flood event that overwhelms stopbanks and other constructed flood defences. Through a combination of historical records and modelling, the Council has been able to characterise the nature of likely flood events. The different flood hazard levels in the policy (in terms of depth and velocity) reflect the potential severity of flooding. Flood risk increases from Level 1 to Level 4, creating a hierarchy of flood risk. The hierarchy allows the management of flooding to be specifically tailored to reflect the risk. In other words, avoiding or mitigating a Level 1 flood risk requires a different response to avoiding or mitigating a Level 4 flood risk. This is reflected in subsequent policies. The four levels of flood risk will each be represented by separate flood hazard overlays. An annual recurrence interval of 50 years has been used as the relevant measure of flood risk as it reflects the standard specified in the New Zealand Building Code for managing flood risk to buildings. Level 2 and Level 3 also include land within or in close proximity to lakes, rivers and wetlands. This is because this land has a greater potential to be flooded. It also ensures that the risk of flooding is managed where no historical records exist or where no modelling has been undertaken. Level 4 is an extreme flood event and is rarer than a flood with an annual recurrence interval of 1 in 100 years. [D] Policy 11.1.10 – Control the erection and placement of houses and other habitable structures within areas subject to a flood hazard overlay, and reduce the risks to life and property by: (a) establishing minimum floor levels for houses and other habitable structures subject to a Level 1 flood risk, set at least 450 mm above the natural ground level as measured at any point of the building footprint. The building footprint includes any associated on-site wastewater management system; (b) requiring houses and other habitable structures subject to a Level 2 flood risk to be subject to evaluation of the flooding hazard and effective mitigation actions; and 11 – 5