NZ Historic Weather Events Catalogue
March 1986 Canterbury and Otago Flooding
(
1986-03-12
)
100+
Very intense rainstorm brought flooding to large parts of South Canterbury and North Otago resulting in very high damage costs and stock losses.
South Island
Heavy Rain
at
South Island
Duration: 2 days - There was heavy rain over Canterbury and Otago from the 12th to the 13th.
Three features collaborated to make an extreme event. Firstly - there was a tropical cyclone near Kermadecs. Warm air from this system spread down onto the South Island in a weak anticyclonic flow. At this point, the air became caught up in a second system – a large, slow-moving depression was centred in the Tasman Sea. The third system, a high-latitude anticyclone, then brought cool southeasterly air up the east coast of the South Island. Convergence between cool air and warm tropical air then led to intense convection. Thermal gradient in the lowest 3-500 metres across convergence zone was 6-7ºC.
300 hPa analysis for 6am on the 13th shows the South Island lying within a strongly difluent flow, in poleward exit region to a jet stream. Strong upward motion is therefore indicated. Cloud tops temperatures were –60 to –70ºC, indicating cloud top heights of around 13,000m. At around this time, Rangiora was raining at up to 37mm/h. As the high to the south moved northeastwards, flow over Canterbury turned northeast, and the convergence zone broke up.
Flooding
The insurance industry payouts in Canterbury and Otago was $18,500,000 ($37,720,000 2004 dollars).
Heavy rain in the foothills of the Southern Alps generated the region's largest flood in more than 100 years.
Water overflowed the stopbanks and escaped onto the floodplains causing major damage.
Canterbury
Heavy Rain
at
Canterbury
The highest rainfall occurred in the Timaru district and the western foothills of Ashburton, especially Peel Forest. Rainfall with an average recurrance interval (ARI) of at least 100 years occurred from Woodbury to Cave and across Timaru.
Heavy rain resulting in serious flooding throughout the region in the 24 hours up to 9am on the 13th.
In some places total rainfalls reached up to 25.0cm.
There were areas that received a burst of up to 5.0cm in two hours at the end of the downpour.
A heavy rain warning was issued, but it was too late to be of any real use to catchment authorities.
Flooding
There was a Civil Defence Declaration over the whole region from the 13th to the 16th.
There was a Civil Defence Declaration over the Aorangi Region from the 13th to the 24th.
There was a Civil Defence Declaration for Strathallan County, Waimate Combined District, Temuka Borough and Timaru City.
Waihao River had a peak discharge of 1250 cumecs (the design flood was at 800 cumecs).
DRC was appointed on 16/03/1986 for 28 days, renewed for 28 days and concluded on 28/05/1986.
1160 people were evacuated from Pleasant Point to Timaru.
200 people were evacuated from Seadown to Temuka.
Rail and road damage was estimated at $30,650,000 (1991 dollars).
Agricultural assistance was estimated at $4,670,000 (1991 dollars).
All rivers in the district in high flood especially Orari River.
Floods,slips, washouts and surface flooding occurred in areas near and south west of Rangitata River.
The effect of the flood was enhanced by the already high soil moisture content, preceding the event.
The damage cost to the whole of south Canterbury was estimated at $60,000,000 ($103,000,000 2004 dollars) to property, roads, railway lines, bridges, crops and livestock. Other damage costs included another $6,170,000 ($11,671,000 2004 dollars) to river control works such as embankments, groynes and plantings.
Many roads were scoured.
The estimated return period for the flood was 100 years.
There was one casualty.
Nearly $15,000,000 of stock were lost due to the floods ($30,000,000 2006 dollars).
There was extensive flooding around Pleasant Point and Geraldine.
Flooding
at
Geraldine
Geraldine reported its worst flood since 1929.
Flooding
at
Hakataramea Valley
Within Hakataramea Valley, all farmers were forced to evacuate their farms .
Heavy Rain
at
Heatherleigh
Heatherleigh recorded 16.7mm of rain in 24 hours (which has a return period of over 100 years).
Heavy Rain
at
Kakahu Bush
Kakahu Bush recorded 14.5cm of rain in 12 hours (which has a return period of over 150 years).
Heavy Rain
Kakahu Bush recorded 10.6cm of rain in six hours (which has a return period of over 150 years).
Flooding
at
Pareora River
The Pareora River was at a flow estimated to occure only once every 150 years.
Heavy Rain
at
Peel Forest
Peel Forest recorded 15.0cm of rain in three days.
Heavy Rain
at
Pleasant Point
The most intense rainfall occurred in the Tengawai River catchment, flooding Pleasant Point up to a depth of 1.5m.
1200 people were evacuated as the Tengawai River burst its banks and water up to
Heavy Rain
at
Rangiora
Rangiora recorded 10.1cm of rain in six hour ( which has a return period of over 150 years).
Heavy Rain
at
Timaru Airport
Timaru Airport recorded 7.0cm of rain in six hours.
Heavy Rain
at
Woodbury
Woodbury recorded 19.3cm of rain over 24 hours.
Otago
Multi Hazard
at
Otago
Very intense rainstorm brought flooding to large parts of South Canterbury and North Otago.
References
- Burgess, S.M. (1986). New Zealand Weather. Weather and Climate (1986)6:80-82.
- Headline: Civil Defence declaration since 1 January 1963.
- Declared Civil Defence Emergencies,
- Insurance Councils, The Cost of Weather Loses, Claims History (Updated 2004)
- Major weather events in New Zealand, FLOODS AND HIGH RAINFALL, Floods to 31st July 2006
- Meteorological Observations for 1986, Stations in New Zealand and Outlying Islands, and Antarctica. New Zealand Meteorological Service.
- Mosley, M.P., and Pearson, C.P. (1997). Floods and Droughts: The New Zealand Experience.
- NZ Met Service. (2008). Meteorology of Extreme Rainfalls in New Zealand (Mark Pascoe, Ed.).
- Headline: Dam may have prevented flood.
- The Press, 22 April 1994.
- Headline:Major South Island Floods
- The Press,11 August 2007,
March 1986 Canterbury and Otago Flooding
(
1986-03-12
)
100+
Very intense rainstorm brought flooding to large parts of South Canterbury and North Otago resulting in very high damage costs and stock losses.
South Island
Heavy Rain
at
South Island
Duration: 2 days - There was heavy rain over Canterbury and Otago from the 12th to the 13th.
Three features collaborated to make an extreme event. Firstly - there was a tropical cyclone near Kermadecs. Warm air from this system spread down onto the South Island in a weak anticyclonic flow. At this point, the air became caught up in a second system – a large, slow-moving depression was centred in the Tasman Sea. The third system, a high-latitude anticyclone, then brought cool southeasterly air up the east coast of the South Island. Convergence between cool air and warm tropical air then led to intense convection. Thermal gradient in the lowest 3-500 metres across convergence zone was 6-7ºC.
300 hPa analysis for 6am on the 13th shows the South Island lying within a strongly difluent flow, in poleward exit region to a jet stream. Strong upward motion is therefore indicated. Cloud tops temperatures were –60 to –70ºC, indicating cloud top heights of around 13,000m. At around this time, Rangiora was raining at up to 37mm/h. As the high to the south moved northeastwards, flow over Canterbury turned northeast, and the convergence zone broke up.
Flooding
The insurance industry payouts in Canterbury and Otago was $18,500,000 ($37,720,000 2004 dollars).
Heavy rain in the foothills of the Southern Alps generated the region's largest flood in more than 100 years.
Water overflowed the stopbanks and escaped onto the floodplains causing major damage.
Canterbury
Heavy Rain
at
Canterbury
The highest rainfall occurred in the Timaru district and the western foothills of Ashburton, especially Peel Forest. Rainfall with an average recurrance interval (ARI) of at least 100 years occurred from Woodbury to Cave and across Timaru.
Heavy rain resulting in serious flooding throughout the region in the 24 hours up to 9am on the 13th.
In some places total rainfalls reached up to 25.0cm.
There were areas that received a burst of up to 5.0cm in two hours at the end of the downpour.
A heavy rain warning was issued, but it was too late to be of any real use to catchment authorities.
Flooding
There was a Civil Defence Declaration over the whole region from the 13th to the 16th.
There was a Civil Defence Declaration over the Aorangi Region from the 13th to the 24th.
There was a Civil Defence Declaration for Strathallan County, Waimate Combined District, Temuka Borough and Timaru City.
Waihao River had a peak discharge of 1250 cumecs (the design flood was at 800 cumecs).
DRC was appointed on 16/03/1986 for 28 days, renewed for 28 days and concluded on 28/05/1986.
1160 people were evacuated from Pleasant Point to Timaru.
200 people were evacuated from Seadown to Temuka.
Rail and road damage was estimated at $30,650,000 (1991 dollars).
Agricultural assistance was estimated at $4,670,000 (1991 dollars).
All rivers in the district in high flood especially Orari River.
Floods,slips, washouts and surface flooding occurred in areas near and south west of Rangitata River.
The effect of the flood was enhanced by the already high soil moisture content, preceding the event.
The damage cost to the whole of south Canterbury was estimated at $60,000,000 ($103,000,000 2004 dollars) to property, roads, railway lines, bridges, crops and livestock. Other damage costs included another $6,170,000 ($11,671,000 2004 dollars) to river control works such as embankments, groynes and plantings.
Many roads were scoured.
The estimated return period for the flood was 100 years.
There was one casualty.
Nearly $15,000,000 of stock were lost due to the floods ($30,000,000 2006 dollars).
There was extensive flooding around Pleasant Point and Geraldine.
Flooding
at
Geraldine
Geraldine reported its worst flood since 1929.
Flooding
at
Hakataramea Valley
Within Hakataramea Valley, all farmers were forced to evacuate their farms .
Heavy Rain
at
Heatherleigh
Heatherleigh recorded 16.7mm of rain in 24 hours (which has a return period of over 100 years).
Heavy Rain
at
Kakahu Bush
Kakahu Bush recorded 14.5cm of rain in 12 hours (which has a return period of over 150 years).
Heavy Rain
Kakahu Bush recorded 10.6cm of rain in six hours (which has a return period of over 150 years).
Flooding
at
Pareora River
The Pareora River was at a flow estimated to occure only once every 150 years.
Heavy Rain
at
Peel Forest
Peel Forest recorded 15.0cm of rain in three days.
Heavy Rain
at
Pleasant Point
The most intense rainfall occurred in the Tengawai River catchment, flooding Pleasant Point up to a depth of 1.5m.
1200 people were evacuated as the Tengawai River burst its banks and water up to
Heavy Rain
at
Rangiora
Rangiora recorded 10.1cm of rain in six hour ( which has a return period of over 150 years).
Heavy Rain
at
Timaru Airport
Timaru Airport recorded 7.0cm of rain in six hours.
Heavy Rain
at
Woodbury
Woodbury recorded 19.3cm of rain over 24 hours.
Otago
Multi Hazard
at
Otago
Very intense rainstorm brought flooding to large parts of South Canterbury and North Otago.
References
- Burgess, S.M. (1986). New Zealand Weather. Weather and Climate (1986)6:80-82.
- Headline: Civil Defence declaration since 1 January 1963.
- Declared Civil Defence Emergencies,
- Insurance Councils, The Cost of Weather Loses, Claims History (Updated 2004)
- Major weather events in New Zealand, FLOODS AND HIGH RAINFALL, Floods to 31st July 2006
- Meteorological Observations for 1986, Stations in New Zealand and Outlying Islands, and Antarctica. New Zealand Meteorological Service.
- Mosley, M.P., and Pearson, C.P. (1997). Floods and Droughts: The New Zealand Experience.
- NZ Met Service. (2008). Meteorology of Extreme Rainfalls in New Zealand (Mark Pascoe, Ed.).
- Headline: Dam may have prevented flood.
- The Press, 22 April 1994.
- Headline:Major South Island Floods
- The Press,11 August 2007,