This chapter establishes an overall framework for natural hazard management under the RMA. It also sets out the division of responsibilities between the Regional Council and Territorial Authorities for natural hazard management under the RMA.

The Region is vulnerable to a number of natural hazards. The principal threat is from flooding. Other natural hazards include earthquakes, tsunami, volcanic action and land subsidence. Climate change is likely to influence the frequency, scale or intensity of atmospherically influenced natural hazards such as flooding. The vulnerability of the Manawatū-Whanganui Region to natural hazard events is increased because of human activity such as:
  • land disturbance* and vegetation clearance*, particularly on hill slopes in a Hill Country Erosion Management Area*, which can increase the erosion risk and the amount of sediment in the flood channel, in turn increasing the intensity of, and effects from, floods and reducing the effectiveness of mitigation measures such as stopbanks
  • the increasing number of people living in hazard-prone areas (including associated infrastructure) such as along the coast and adjacent to rivers, which increases the damage potential from natural hazard events, putting lives at risk. It can also reduce the effectiveness of existing mitigation measures such as stopbanks.

Most of the Regional Council’s operational work on natural hazard management is carried out under the Soil Conservation and Rivers Control Act 1941, which provides for the establishment of river and drainage schemes. Emergency response, community readiness, recovery planning and research into natural hazard risks, is carried out under the Civil Defence and Emergency Management Act 2002. These roles are implemented through the Civil Defence and Emergency Management Group Plan rather than through the One Plan. The role of the Regional Council and Territorial Authorities under the RMA is primarily one of risk reduction to ensure that resource use activities do not exacerbate natural hazard risks or impede natural hazard mitigation works, thereby ensuring that developments do not put people or property in places or circumstances of undue risk.

The approach to managing natural hazards in this Plan is to:
  1. set out a clear regional framework for natural hazard management,
  2. improve clarity around the respective roles of the Regional Council and Territorial Authorities under the RMA,
  3. discourage future residential development and placement of critical infrastructure* in areas prone to natural hazard events, particularly areas at high risk of flooding, and
  4. continue to provide information to Territorial Authorities and the general public with regard to natural hazards.
Flooding occurs frequently in the Region. The impacts of floods are mostly localised, but the likelihood of a major flood occurring in any year is high. The February 2004 storm event caused widespread flooding. Recovery from that event will span many years. It showed only too well the problems that can arise from the combination of such a large storm event with vegetation clearance* on hill slopes and residential settlements and infrastructure on flood-prone or unstable land. The resulting sedimentation in water bodies and erosion on land has impacted on infrastructure, people, land use and the natural environment.

Today over half of the Region’s population lives on the floodplains of the major rivers. The establishment of river and drainage schemes (with the associated construction of stopbanks, floodgates, spillways and retention dams) has been an integral part of the development of the Region. Current schemes undergo regular review and assessments are undertaken for areas that could be included in these schemes or established as new schemes. More information on minimising the effects of erosion and flooding on the beds of rivers and lakes can be found in Chapter 5.

Hill country erosion and coastal erosion are both of concern, as human activity has the potential to greatly increase erosion risk and associated impacts on people and property. Hill country erosion is addressed in Chapter 4.

Other natural hazards
Other natural hazards that occur less frequently include earthquakes, volcanic action, land subsidence and coastal environment hazards (including tsunami, storm surge and sea level rise* hazards). Despite their low frequency, they have potential to put the Region at risk. Although little is known of the risks of these hazards, current research, such as the Regional Council’s tsunami hazards study, will enable better future planning. Due to limited knowledge of the influence climate change may have on some natural hazard events, a precautionary approach to establishing or intensifying land use activities in areas potentially subject to natural hazards is required. Potential impacts will continue to be dealt with by contingency planning, such as the regional civil defence response team and insurance schemes, until further research can be undertaken.