Volume One 11. Natural Hazards [RPS, R, D] Policy 11.1.2 – In conjunction with Civil Defence, provide an emergency response to natural hazard events. The provision of an emergency response to a natural hazard event is important in managing the adverse effects of the hazard. The Council is actively involved in the provision of a response to natural hazard events for which they are the lead agency, including floods, urban stormwater, sewer or water supply failure. The Council may also provide support or ancillary services to agencies leading the response to other emergency events such as earthquake or major fire. Once a state of local or national civil defence emergency has been declared, the Council will continue to provide services under the direction of the Civil Defence Controller. Details of the roles and responsibilities of emergency agencies and a commitment to a coordinated and collaborative approach to hazards events are included in the CDEMP. This policy also records the intent to continue to be involved in emergency responses on an ongoing basis and recognises that the role of the Council is complimentary to that of Civil Defence. Flooding – Flood management [R] Policy 11.1.3 – To actively manage any flood hazard through the provision and maintenance of flood defences and other flood mitigation works, where there is significant community benefit. One of the means of reducing the risk of flooding is to provide flood defences to protect the existing population, properties and community infrastructure. On the Lower Wairau Plain, a significant investment has been made over a considerable period of time to protect Blenheim, other towns and the surrounding rural land through the construction and maintenance of stopbanks and the training and diversion of rivers. The Waitohi and Waikawa Rivers in Picton are the only other rivers to which the Council has administered flood defences. The costs of managing flood hazards are significant. This policy identifies a threshold for justifying such intervention. The initial expenditure to establish flood defences and the ongoing maintenance expenditure must be warranted by significant community benefit. Those benefits will have to be identified and evaluated on a case-by-case basis. This policy is also moderated by the remaining provisions of this chapter, which seek to avoid or mitigate the adverse effects of flooding by management of new land uses in flood prone areas. This should reduce the demand for additional flood defences. [R] Policy 11.1.4 – Establish and maintain floodway capacities for Marlborough’s rivers to the following standards: (a) to an annual recurrence interval of 1 in 100 years for major rivers on the Wairau River floodplain (below the confluence with the Waihopai River); (b) to an annual recurrence interval of 1 in 50 years for the Waitohi and Waikawa Rivers; and (c) to an annual recurrence interval of 1 in 50 years for rivers and drainage channels that provide for urban stormwater disposal. This policy establishes standards for the rivers for which the Council provides flood defences. It also applies to rivers and drainage channels that receive urban stormwater discharges. An annual recurrence interval is the expected period between river flows of a particular magnitude (in other words, a flood of that magnitude has a certain probability of being exceeded in any year). Historical records of flood flows are used to determine the annual recurrence intervals specified in the policy. The standards in (a) to (c) reflect those adopted by the Council in the Rivers and Land Drainage Asset Management Plan. They provide a measure of the level of protection provided by 11 – 3