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Flooding

The Marlborough District Council has a major role in alleviating flood situations to reduce threat to life, damage to property and to keep roads and other infrastructure operating.

Real-Time On-line Flood Information

Flood Watch

Flood Watch is an informative, easy-to-use web-based mapping tool to help you judge if there is a flood risk in your area. The Flood Watch map displays current rainfall, river flow and river level data from monitoring sites around Marlborough.

See more information on Flood Watch

Flood Watch  View Flood Watch

Flood Index Map

The current river levels at Council's recorders and recent rainfall amounts can be accessed directly from the Flood Index Map. The river levels are shown compared to normal and rainfall is shown for the last three days.

The rainfall data is collected as the rain is falling and river level data as rivers rise. This is done at several sites throughout Marlborough and telemetered to Council's Blenheim office. During floods this data is collected every few hours. 

Hydrotel System

Alternatively, actual rainfall data and riverflow data can be viewed on Council's Hydrotel system.

Flood Infoline Answerphone

A summary of the data is also recorded on Council's River and Flood Infoline answerphone system, Ph: +64 3 520 7488.

  • The InfoLine gives up-to-date river levels and recent rainfall from the Council's recorders throughout Marlborough, so as to warn of probable flooding.
  • This flood warning advice should be used as the basis to move stock or machinery from the riverbed.
  • The information is also useful for river recreational users.
  • The InfoLine is updated frequently during flood events and at other times twice weekly.

Explanatory Notes about Flood Level Information

  1. Wairau (including Waihopai and Branch)
    For the Wairau River upstream of the Waihopai River, the Branch River recorder is a good indicator of flood conditions. A Branch flood level greater than 1 m above normal threatens Wairau River flats. Farmers living in the Wairau Valley area will get a Wairau flood about six hours later than for the Branch River. Rainfall at Top Valley rain-gauge is also a useful indicator of a likely flood. Rainfall at Top Valley exceeding 50 mm in the previous nine hours is a likely indicator of a flood in the Wairau or its tributaries above Waihopai. River flood level information is also available for the Waihopai River.

    The Wairau at Tuamarina recorder is indicative of flood conditions for the main Wairau floodplain. The Council can predict flood levels here up to nine hours in advance from rainfall. A flood level greater than 2 m above normal threatens Wairau floodway land. A flood rise greater than 3 m floods the Wairau Diversion and Lower Wairau floodway land. Rainfall at Onamalutu rain-gauge is also a useful indicator of a likely flood. Rainfall at Onamalutu exceeding 50 mm in the previous nine hours is a likely indicator of a flood in the Wairau on the floodplain. Rainfall exceeding 75 mm on the floodplain measured at Wairau rain-gauge is also an indicator of local flooding or drainage impairment.
  2. Omaka (Opawa, Taylor, Doctors, Fairhall, Gibsons, etc.)
    The Omaka at Tyntesfield Gorge is a good indicator of expected floods in the Upper Opawa some six hours or so later and Roses Overflow later still. A flood level of 0.8 m above normal will close the Old Renwick Road ford. A flood level greater than 1.8 m above normal will result in flooding of floodway berm land and closure of other road fords. An Omaka, flood level exceeding 1.8 m above normal is also indicative of flooding in other southern valley rivers such as Doctors Creek, Fairhall, Gibsons Creek etc. Floodway berm land in the Opawa/Taylor becomes flooded as the Taylor Dam outflow exceeds 50 m³/sec. Rainfall exceeding 50 mm in the previous nine hours at Tinpot rain-gauge in the Taylor catchment is also an indicator of likely flooding in the Southern Valleys and the Awatere area.
  3. Sounds (Rai, Pelorus, etc.)
    The Council has less information for the variable Marlborough Sounds rivers. A flood level rise of greater than 2.5 m in the Rai River at Rai Falls is indicative of a flood in the downstream Rai and Pelorus rivers. Rainfall exceeding 75 mm in the previous nine hours at Tunakino rain-gauge is indicative of likely potential flood problems in the Marlborough Sounds.

Discussion of Flood Sizes

There are varying levels of floods:

  • Major Floods
    These occur when the Wairau, Omaka or Opawa rivers break out of their floodway stopbanks and can be life-threatening. The Police, Civil Defence organisation and other agencies will be involved, with radio stations used for messages to the public. The township of Blenheim has been hit by flood, but major floods are rare. The last was the July 1983 flood of the Wairau River.
  • Moderate Floods
    These occur when minor river breakouts occur, perhaps from smaller rivers such as the Pukaka or Waitohi, or from Gibsons Creek, or minor overflows from the bigger rivers of Wairau, Opawa or Taylor. Life is not directly threatened by moderate floods, but there is potential damage to farm stock, houses and property. Roads are often closed. Civil Defence is not involved. Such events occur typically once every five years and last occurred in July 1998, involving many rivers in the district.
  • Small Floods (freshes)
    These occur predominantly in the Wairau River and affect farmers and contractors using riparian or floodway land. Stock and machinery need to be moved to higher ground. These floods typically occur every four months.

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