Rain started to fall along the coast on Friday, continuing through the weekend and easing in most places only yesterday morning.
MetService had predicted a low pressure system could bring up to 150mm around the region and rainfall totals reached a high of 166mm at Pine Hill, Dunedin, down to a low of 40mm at Nenthorn Stream, in Strath Taieri.
The rain saw Dunedin make up for what had until Friday been a dry month. On Friday, Musselburgh had received only 24.5mm of rain and the airport 25.6mm, but by 8pm on Monday, the monthly rain totals had risen to 108.6mm and 75mm respectively. The average rainfall for February is 63.2mm at Musselburgh and 58.2mm at the airport.
Otago Regional Council environmental information and science director John Threlfall said the lack of "big intensity" falls, combined with very dry ground, meant many rivers, while running high yesterday, were keeping within their banks.
The Kakanui River, which earlier last week was at only 48% of its long-term average, received 127mm of rain, bringing it to a peak of 350cumecs at Mill Dam. It passed its first flood warning level at Clifton Falls bridge at 8am on Saturday.
Most rainfall sites in Dunedin had an hourly maximum rate of between 4mm and 7mm, compared to a normal Silver Stream flooding event, where rates ranged from 9mm to 18mm an hour. Sullivans Dam received 114mm at the weekend compared to 156mm in July 2008, 147mm in July 2007 and 249mm in April 2006, falls which all produced large floods in the Silver Stream.
"The volumes were similar, but it was moderate rainfall, over a long period of time, rather than big pulses," Mr Threlfall said.
It was very much a coastal rain pattern with falls reducing to less than 50mm further south and inland, he said.
There was also quite a variation in intensity of rainfall, with some areas receiving light drizzle and others moderate rainfall, so rivers responded accordingly, he said.
Garth Mitchell, who farms at the foot of Mt Maungatua, recorded 170mm from Friday to Sunday, with 70mm falling between 9am and 7pm on Sunday. A localised cloudburst on his property about 3pm on Sunday caused surface flooding along Maungatua Rd and scoured out many of the small streams and creeks in the area.
"The heavens just opened and it poured down, but a neighbour who lives about 1km away as the crow flies was standing outside without a jacket on," he said.
Otago Daily Times weather contributor John Bradley, who has been recording weather statistics for more than 30 years, said the last time Dunedin experienced such rain volumes at this time of year was in February 2005 (149mm) and in January 2002 (178mm).
"This is the most beautiful long-term rain I've ever seen. There has been no run-off, no scouring, no flooding around here."
Dunedin City Council roading maintenance engineer Peter Standring said as the rain was only a persistent drizzle, over a long period, it was easier to manage and did not cause as much damage.
A bridge at Wingatui had been closed for a short period and there had been some small slips on Otago Peninsula but "nothing out of the ordinary", he said.
• Rainfall Feb 20-23
Pine Hill: 166mm
Balaclava: 134mm
St Clair: 95mm
Broad Bay: 119mm
Mosgiel: 61mm
Green Island: 107mm
Silver Stream at Swampy Spur: 137mm
Deep Stream at SH87: 53mm
Balclutha: 53mm
Kakanui at Clifton Falls Bridge: 127mm
Kauru at The Dasher: 114mmSources: ORC, private individuals, DCC
