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Flooding & Storm Events in Hawke's Bay

Floods and storms are the most frequent hazard in Hawke’s Bay. Many major damage causing floods have been recorded in Hawke’s Bay, and stopbanks, pumping stations and other protection measures have been put in place. Find out what you need to know, how to prepare, what to do when it happens and also what to do after the event.

What warning will there be?

Usually there will be sufficient warning of a storm.  Keep up to date with daily weather forecasts online (websites and apps ) or through radio and television. You can sign up to receive MetService Severe Weather Warnings and Watches as they are issued – the MetService has good information on the services it provides.

However sudden storms and flash flooding can occur without warning in individual catchments.

How do I get prepared?

  • Find out about floods in your location and how high the worse of these got– check the flooding information on hazard portal. Calculate where a similar flood would reach in your home and know how you can reach the nearest high ground.
  • Make sure you have appropriate household and contents insurance and keep those details handy.
  • If you live in a flood prone area, consider storing sandbags to protect your home in a flood situation. Know what to do if a flood happens and how you can get out.
  • Farmers and lifestyle block owner need to consider how and where you will relocate stock in a flood situation.

Learn more at Get Thru.

What to do when it happens and after?

Neighbourhood

  • Never assume that you are safe close to a river, stream, drain or other type of waterway during a flood. The water may overtop banks or erosion could cause the ground around waterways to give way. Debris can also build up blocking waterways creating dams which have potential to suddenly release a large volume of water.
  • Stopbanks are designed to provide a specific level of protection from flooding.  However if it has been raining heavily for a while and the river/stream has risen high, this can increase the risk of water over-topping or breaking a hole in the stopbank. If you and your family feel at risk, leave immediately and contact the local council.
  • If you are by the coast or at the beach, be wary of storm surges. It can be particularly dangerous around river mouths and low lying areas. Avoid situations where you could get cut off or swept into the water.
  • In town, flash flooding can overwhelm the stormwater system and cause surface flooding. In flat urban areas – like Napier and Hastings – pumping is needed to get stormwater out of drains and it can take a while to clear backed up water.

Home and business

  • If you feel at risk of flooding and can leave safely, get to higher ground.
  • Lift valuable household items and chemicals above the estimated high-water mark for flooding.
  • If strong winds are forecast, make sure heavy items (trampolines, garden furniture, gazebos) are taken indoors or well secured.  Flying objects will break windows, damage other property and even kill people.
  • Turn off power, gas and water if told to do so by authorities as this can help prevent damage to your home or community. Unplug small appliances to avoid damage from power surges.
  • Do not attempt to drive or walk through floodwaters.  There can be unknown hazards, like open drain holes and debris, and unseen hazards such as septic tank and sewage pollution.
  • Blocked gutters and down pipes can mean water gets into your roof and inside your walls causing damage and electrical faults.
  • If your property is damaged, take photos and contact your insurance provider as soon as possible.
  • Renters should contact their landlord if there’s any damage.

Floods may be listed as Hawke’s Bay’s number 5 hazard, but it is our most frequent hazard in terms of losses and declared civil defence emergencies.

Much of the built up and farmed areas of Hawke’s Bay are on low lying land and river flood plains. This means there is a risk of flooding.

Frequency of storms and floods

A severe storm or flood happens every 10 years on average.

Major storms affect wide areas and can be accompanied by strong winds, heavy rain or snowfall, thunder, lightning, and rough seas. They can cause damage to property and infrastructure, affect crops and livestock, disrupt essential services and cause coastal inundation.

Rivers normally flood every winter when a storm brings more rainwater than can soak into the soil. In Hawke's Bay stopbanks have been built alongside many of the rivers to hold in the extra flood water. However in a severe storm, rivers could breach stopbanks and the flood waters may go through farms, homes, shops, schools and damage roads and other infrastructure.

Examination of the rainfall and flood records shows that there have been long periods without major floods and other periods where they have been more frequent.

Common Factors in Floods

The common factors in most flood events in Hawke’s Bay are:

  • Heavy prolonged easterly or southeasterly rains.
  • The greatest percentage variation of rainfall in New Zealand, with hot dry spells followed by heavy rains, resulting in high runoff across dry land.  Climate change is expected to intensify this variation.
  • Comparatively shallow soils. Our soils have limited capacity to absorb large amounts of rainfall. Plus impermeable layers underneath, especially mudstone, does not let water through.
  • Short, steep catchments in the hill country.  These result in rapid runoff, and are further  aggravated by highly erodible soils.
  • A lack of lake/wetland storage with few ponding areas.  Draining and filling in of almost all wetlands/swamps in Hawke’s Bay over the centuries has not helped, which is why many wetland restoration projects are underway to improve flood protection plus water quality and biodiversity values.
  • Three major rivers on the Heretaunga Plains - the Ngaruroro, Tukituki and the Tutaekuri. These discharge into the sea within about 5 km of each other, causing water to back up, especially if there is a strong prevailing easterly wind and current and/or high tide.
  • Many major river headwaters in areas where the rainfall averages are much higher than the plains. The annual rainfall for the ranges is 3500 mm a year - compared to only 800 mm for the Napier/Hastings area.

Stopbanks and other flood protection systems

Almost immediately after the 1886 flood which flooded most of Meeanne, Hastings and parts of Napier and changes the course of the Ngaruroro River, local people started to demand stopbank protection for their land, property and families.

Hawke’s Bay people and property are now protected from flooding by a significant network of stopbanks and protection systems on both the Heretaunga Plains and the Ruataniwha Plains.

Level of protection

These flood protection works are designed to contain a 1% annual exceedance probability flood – which is the same as saying a flood with a 1 in 100 chance of occurring in any one year and a 10% chance of occurring in any 10 year period.  

These protection works have significantly reduced the effect of small to medium sized floods on surrounding land and property, but a large flood could still overwhelm the protection systems and have a devastating effect. Such a flood is called a Super Design Flood because it is exceeds the water capacity that the flood protection system has been designed to.

Flooding from localised downpours in urban areas can also overwhelm drainage systems, especially in the cities which are on flat land and rely on pumping for drainage.  These local storms/flash floods often aren’t able to be predicted.

Climate Change Effects

With climate change, rainfall patterns in the Hawke’s Bay will change over the next century; winters are predicted to become drier, but overall flood risk is not expected to decrease as single events may be more intense.

 

 

 

 

 

 

History

By national standards Hawke’s Bay’s rivers are not large with the exception of the Wairoa and Mohaka Rivers. However, many major damage causing floods have been recorded. Individual floods have ranged in size from cyclonic storms that have caused regional flooding to localised downpours that have affected minor catchments or caused drainage systems to overflow.

Since 1867 there have been numerous major storms resulting in severe flooding in Hawke’s Bay (see the Table below [insert from current website]). You can learn more about these events on the NIWA historical weather events database.  

flooding 5Type of Event: Flood
When: 18 October 2004
Where: Napier

A thunderstorm dumped several days' worth of rain on Napier in just a few hours. Described as a rain bomb, this deluge was a 1/50 year event. Rain quickly filled drains and then covered roads, which are constructed below the level of properties to act as large drains.

However, the rain was so intense (up to 180mm of rain was recorded in a few hours in the epicentre of Tamatea/Greenmeadows) that water then spilled over into numerous properties. Eight homes were flooded as well as businesses in the Onekawa industrial area. Losses were estimated in the millions of dollars.

Summary of Events

  • On Sunday, 17 October 2004, Metservice issued a heavy rain warning for Hawke's Bay. Heavy rain started to fall late that day.
  • In the early hours of Monday, 18 October, Napier City Council Services staff, the Fire Service and Police responded, increasing their activities as the rain steadily intensified to a peak over a period of four hours.
  • An electrical storm and hail accompanied this weather front and downpour.
  • Napier City Council's Services Department Depot office was activated and began managing pumping and drainage operations.
  • The Fire Service established an operations centre at Napier Fire Station, although the Wellington Communications Centre continued managing calls and deployment.
  • Napier Police responded to the Napier Fire Station, coordinating the resources of both organisations.
  • As water levels rose, ground-sited electrical transformers began failing. Electrical reticulation was disrupted and as many as 2000 homes lost power.
  • Telephone services also experienced some disruption.

Situation During Peak Flooding

Council Services staff, the Fire Service and Police closed a number of roads to minimise the impact of vehicle bow wave action. Many roads and properties in Napier's southern suburbs were flooded including in Taradale, Tamatea, Pirimai, Greenmeadows and the more rural area of Meeanee.

Fortunately, because of the design of Napier's road profile, very few homes were affected by floodwater.

The Fire Service mobilised the Salvation Army to cater for emergency workers at the Napier Fire Station. The Salvation Army catered for over 60 staff and 10 displaced people.

The Salvation Army Centre in Greenmeadows was offered as a refuge for those who needed it, and some 12 residents from that area visited the centre.

Police and the Fire Service assisted a number of stranded motorists to get to higher ground.

All the agencies involved in the response coped well and additional assistance was not required, so the threshold for declaring a state of emergency was not met.

Access was limited to some schools, including Tamatea Intermediate. Student safety and the risk of power failure were also considered in not reopening a number of schools on 19 October.

Property Count

  • Napier City Council is aware of eight properties where floodwater entered the houses.
  • More than 100 plus commercial and industrial premises may have also been affected.

Napier Civil Defence Response

  • Hawke's Bay Regional Council advised Civil Defence that 111mm of rain had fallen in Taradale and 137 mm in Tamatea.
  • The Napier Emergency Operations Centre (EOC) was partially activated with a Local Controller, Civil Defence Manager, Napier City Council's Chief Executive and a Communications Volunteer.
  • Local Volunteers were put on standby and asked to provide communications from around the city and report on the changing situation.
  • The Napier Civil Defence Controller met regularly with Emergency Services and the Napier City Council's Services Department and Works Assets Department at the Napier Fire Station to keep up-to-date on the situation.

Standing Down

  • By mid morning on 18 October most of the floodwaters had receded. Pumping stations continued working to discharge remaining floodwaters, completing the mop-up by nightfall.
  • There were no formal evacuations. Residents who left their homes made their own arrangements for relocation.
  • Restoration of power was complete by end of day on 18 October.

The Maraekakaho community was flooded in July 2007. A few houses were evacuated, while others were accessible only to residents.

Type of Event: Cyclone
When: 7 March, 1988
Where: East Coast, North Island

One of the most damaging cyclones to hit New Zealand, Cyclone Bola struck Hawke's Bay and the Gisborne/East Cape region in March 1988. Slowing as it moved over the area, it resulted in continuous torrential rain for three days.

What Happened?

  • Winds up to 100kph toppled trees and tore off roofs.
  • Heavy rain (how many mm?)  resulted in landslides, power outages , shut down or failure of sewage services and road closures.
  • The East Coast of the North Island suffered devastating floods.
  • State Highway 2 was closed in several places by slips and flooding.
  • Three people died when their car was swept away by floodwaters. Two other occupants in the car were saved.
  • Te Karaka, a small settlement inland from Gisborne, had to be evacuated when the swollen Waipoa River came close to flooding the township of 500 people. In another location, people couldn't be evacuated by helicopter, and horses were brought in to get them out.
  • In Gisborne, the water supply pipeline from dams was lost.
  • States of emergency were declared in Wairoa, Gisborne and the East Cape.
  • In Northland torrential rain caused flooding and cut power and telephone services.  A state of emergency was declared in Dargaville. The main water line was washed away with a bridge, disrupting supply to the township.

Other Impacts and Outcomes

  • A Disaster Relief Committee was set up to assess storm damage on the East Coast.
  • A peak rainfall of 916 millimetres over the three days was recorded inland from Tolaga Bay.
  • The most intense rainfall was on steep East Coast hill country. Areas where there had been little or no soil conservation work done or no flood control schemes suffered the worst damage.
  • Flooding affected some 3600 hectares of farming and horticultural land, with the associated losses estimated at $90 million.
  • 1765 farmers were affected by damage to their land and crops and stock losses. Cyclone Bola hit some areas just as harvesting was about to start.
  • Repairs to Gisborne's water supply cost an estimated $6.6 million. Damage to East Coast forests was estimated at $8.6 million.
  • Insurance payouts for the whole event totalled $37 million ($63 M in 2008 dollars), excluding Earthquake Commission claims .
  • An inquiry into flood management followed. Recommendations included soil conservation work, improved river control and management and better land use planning.
Statistics  
Formed February 24, 1988
Dissipated March 4, 1988
Highest Winds 165 km/h (105 mph) (10-minute sustained)
195 km/h (120 mph) (1-minute sustained)
Lowest Pressure 940 hPa (mbar)
Fatalities 3 direct
Damage $87 million (1988 USD)
Areas Affected Fiji, Vanuatu, New Zealand

The Heretaunga Plains in flood in 1935 before stopbanks had been built by the Hawke’s Bay Rivers Board and Hawke’s Bay Catchment Board. This photograph highlights how horticultural land would regularly be flooded if we weren’t protected by stopbanks.

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