By ROSALEEN MACBRAYNE
TAURANGA - The deluge which dumped 51mm of rain on Tauranga in an hour was caused by a rare combination of atmospheric elements, says the MetService.
Sunday's downpour, which left roads and buildings awash, was due to moist tropical air at low levels combining with a depression at upper levels.
Together they produced intense rainfall over a short period, said Allister Gorman of the MetService.
"It was an unusual coming together of several features.
"You get these from time to time around the place, although not always over such a metropolitan area."
He said Tauranga, which had more than twice its average April rainfall in 24 hours, was "just unlucky."
Similar downpours have caused havoc in other areas, such as Auckland city "every now and again" and in Thames two years ago.
The intensity of the rain would have caused surface flooding at any time of the year, not just in autumn when leaves blocking drains were an added feature, Mr Gorman said.
"No drainage system anywhere in New Zealand was designed to take 51mm in one hour."
Yesterday the sun was shining in Tauranga and dried up all the rain - with the help of plenty of pumps and mops.
However, the widespread flooding left silt and debris in its wake.
Director of city services Bruno Petrenas said the Tauranga District Council had recorded 200mm of rain within a 12-hour period, which made it a 100-year event.
"Fortunately, there was relatively little infrastructural damage."
The torrential rain followed a prolonged dry period so the ground soaked up a lot of water before runoff started, he said.
Luckily, it was low tide at the worst of the localised storm.
The rain had eased by high tide at 11 pm, but the runoff was still substantial.
Mr Petrenas said a minimal amount of raw sewage went into the harbour.
Council staff fielded 140 calls during Sunday night, with many more in the morning as people returned to work.
Police and Fire Service telephone lines were also jammed at the height of the drama.
There were many slips throughout the district, although most of them were minor.
Tauranga civil defence manager Barry Low said there was no need to declare an emergency because police and fire services were coping well.
"But we were caught out by an exceedingly heavy rainfall which was not predicted in this part of the world."
He said people needed to take more responsibility for themselves and keep guttering and sumps cleared.
Residents in low-lying areas prone to flooding should keep a few sandbags at the ready.
Mr Low criticised the "total lack of consideration" by some motorists speeding through surface flooding and causing a "bow wave" into roadside properties.
The MetService said that although other North Island areas had suffered heavy rain, it was not as concentrated as it was in Tauranga or on the Coromandel, where no damage was reported.
Tauranga downpour judged as 'bad luck'
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