A deluge of May rainfall records

Flooding throughout Coastal Otago last week may not have broken any records but the rainfall which contributed to it did.

At Dunedin airport last month, 243mm of rain fell (406% of normal), overtaking the previous record of 198.4mm in March 1968, National Institute of Water and Atmospheric Research (Niwa) figures show.

About 235mm of that rain fell between May 24 and 31.

The airport also recorded its highest one-day May rainfall, of 79mm, on May 28.

Oamaru also broke its May record with 203mm (411% of normal).

The previous record was 155mm in May 1917.

In contrast, Otago Regional Council environmental information and science director John Threlfall said while the rainfall was prolonged and caused havoc, the floods did not rank particularly highly compared with historical events.

The flooding was about the third-highest event since the 1986 North Otago floods and also the third-highest on the Taieri River at Outram since 1968.

Some recordings did come close to breaking records, such as the 260.5mm of rain recorded over two days at the Dasher in North Otago, just short of the 265mm that fell in January 2002, he said.

Over two days, Riccarton Rd recorded 178.5mm, just exceeding the 175.5mm in 2006.

The peak flow at the Kakanui River at Clifton Falls was 443cumecs, which was close to the second-highest peak flow of 452cumecs, in July 1994.

However, the Taieri at Outram recorded only 1198cumecs, well short of the June 1980 (2526cumecs) and December 1993 (1467cumecs) floods.

The Silver Stream flow of 133cumecs also fell short of the record flow of 260cumecs, in 2006, as did the Water Leith, reaching a peak of 47cumecs, compared with 95cumecs in 2006.

Rainfall at Sullivans dam of 145.5mm did not reach the record 2006 level of 217.5mm in a day.


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