Storms

An early photo of surface flooding after heavy rain, Patapu Street, Wanganui East.

In Wanganui the most likely consequences of a storm are flooding and strong wind damage.
Images from the July 2006 and February 2004 storms

Deep depressions, tornadoes or cyclonic storm events cause damaging wind.
The National Forecasting Centre issues a strong wind warning when winds are expected to exceed 87 km/h over land. www.metservice.co.nz

What you can do to help yourself

When a strong wind warning is issued:

• Listen to your radio for information.
• Put away or secure any loose objects that may become missiles, including outdoor furniture, light sheds and caravans.
• Check that your survival kit items are all readily available.
• Make sure pets and livestock have safe shelter.

During the storm:

• Close all curtains to help slow down any flying glass or other loose objects.
• Shelter further inside the house, away from doors and windows.
• Use a mattress for added protection.
• If there is lightning about, stay away from electrical fixtures.

After the storm:

Contact your insurance agency and the District Council if your buildings are severely damaged.

Storm event February 2004

The storm emergency of February 2004 was unprecedented in its extent, its effects, and its impact on the Wanganui District. This was the first test of the revised national Civil Defence Emergency Management legislation and the improved regional structure, and resulted in the first regional declaration of emergency since the re-organisation of local government in 1989. Although this major storm affected an area from Ohakune south to Picton, and from Waitotara east to Porangahau, there were no major injuries or fatalities.

The background to this storm is reported (post event) by the MetService as 'a burst of cold air from the Antarctic ice shelf coming north while moist air from a weak tropical low came south. This mixing of moist air with cold air is the perfect recipe for rainmaking'. During the afternoon and evening of Sunday 15 February steady rain started falling over the entire southern half of the North Island. Storm force winds lasted for 29 hours in Cook Strait, and sustained winds over 100 km/hr affected Wanganui.

Heavy rain in the upper catchment caused the Whanganui River to rise to 10.06 metres at the Pipiriki gauge at 9:15am on Monday 16 February. The southerly winds and rain affected the wider Wanganui area and the Matarawa Stream rose rapidly to 2.32 metres at the City Branch gauge at 10.45 am. A band of heavy rain approximately 25 kilometres wide crossed the middle of the district 25 kilometres north of Wanganui City.

Civil Defence Emergency Management staff had been monitoring the position throughout the Sunday night. The Civil Defence headquarters was progressively staffed from 6.00am onwards on the Monday morning. Initially, concerns were with the effects of the windstorm, the potential impact of both the rising Whanganui River and possible flooding in the Matarawa catchment. There had not been any warnings from the Regional Council's Kauangaroa gauge of the event in the Whangaehu River. There has not been any precedent of flooding on that scale of the Whangaehu River.

Initial management of the event was compounded with two significant hardware failures:
- The after hours system was on overload.
- Loss of the Council and Police telephones from 8.00am for several hours.

The Civil Defence Headquarters was in 'response' mode for 19 consecutive days, before the focus was handed to the four 'recovery' teams of: Infrastructure, Economic, Welfare (Property), Welfare (Social), and Rural. Eighteen separate agencies and organisations supported the sustained effort to assist the affected community. Fifty-nine Council staff volunteers in the Headquarters were helped by another 18 community volunteers in the Rescue and Welfare teams.

Subsequent to the storm, a wide variety of debriefing activities have been held, including on-site visits to most of the rural communities, discussions with the supporting voluntary organisations and agencies, the utility companies and the emergency services, as well as volunteers, including Council staff.

Images from the February 2004 storm

Storm event July/August 2006

During 6-7 July 2006, a severe storm caused many slips throughout the Wanganui District, blocking a number of roads and damaging farms. A small number of properties were affected by both flooding and slips, resulting in the evacuation of four houses. Subsequently on July 9, as a result of the weakening of the foundations, the Ngaturi Bridge collapsed, cutting vehicle access to the Whangaehu Valley from the south. (Limited light vehicle access was available from the north involving a detour of approximately 80-90 kilometres). Also, two of Council's water supply bores were temporarily put out of action but no restrictions were necessary.

Significant flooding and slipping occurred in the rural area with immediate loss of stock carrying capacity. The movement of stock was severely restricted because of the condition of the roads, with several thousand stock units due to be transported out of the rural area in the few weeks following the event. A further heavy rainfall event occurred on August 6-7 which set back the recovery efforts and caused significantly more slipping in hill country.

Flooding affected both the lower Whanganui and Whangaehu catchments, though in most instances it was not as severe as in 2004. However, silt damage in some areas was possibly more significant this time. Major slipping occurred in areas that were not severely affected in 2004, particularly in the western area of the District.

Council's Emergency Operating Centre (EOC) was activated mid-afternoon of Thursday, July 6, and closed down late on Friday, July 14. A total of 819 'person hours' from 35 Council volunteers were committed to the response effort over the nine days, with significant support from the remainder of the Council staff to maintain normal service. A number of other volunteers were on standby to assist if the situation escalated, and helped with the 'one month later' activation on August 6 and 7, when 18 staff responded for a total of 130 'person hours'. A good indication of the 'busy-ness' of the situation is the 1300 incoming telephone calls to Council on Friday, July 7; in comparison the average daily number is between 500 and 550 calls. This is a significant difference from the 2004 event when the Council telephone, cellphone, fax and email systems were unavailable for most of the first day, effectively crippling the response efforts.

Early participation in a Transit New Zealand helicopter road survey on Friday, July 7, quickly established the extent of the damage and the potential for a number of isolated residents. A second aerial reconnaissance on Sunday, July 9, assisted with more detailed planning of the road clearance efforts. The Department of Conservation co-ordinated two jet boat trips to move stranded people in the Whanganui River Road area. Twelve helicopter flights were made to deliver groceries, fuel and gas cylinders to isolated residents. The building of the 'flying fox' cableway at the Ngaturi Bridge site for delivery of mail and groceries reduced the need for further helicopter flights to Mangamahu.

Both the February 2004 and the July and August 2007 events presented the Emergency Operations Centre (EOC) with problems in identifying the safety or otherwise of people on the isolated rural roads. The development of the "Lahar Warning" telephone tree amongst the Whangaehu Valley residents was a huge benefit in 2006, with 10 co-ordinators quickly passing information back and forth. The duplication of this arrangement amongst the more vulnerable 'inland' roads will take time and effort, and will always have a percentage of errors. While those residents still have telephone and power services, the contacts via a number of 'road networks' can help establish particular needs for aerial delivery to lessen the isolation factor. Whilst the number of Civil Defence Very High Frequency (VHF) radios in the rural area has been increased, it is not practical to have a radio on every rural road.

Images from the July/August 2006 storm