Why there were no Tauranga floods

Reserves filling with water are actually the stormwater system doing its job. Photo: Rosalie Liddle-Crawford

After years of dealing with city flooding following every heavy rain event, council staff have been slow to take the credit for the Tauranga result following last week's rain which cause floods on the Coromandel, Kawerau – but not Tauranga.

“It's important to note though that we didn't get the level of rainfall that Auckland and Waikato got,” says Tauranga City Council drainage services team leader Wally Potts.

“Our rain gauges show that we received about 220mm to 250mm over six days. This is about 20 per cent of our annual rainfall. However, it was fairly evenly spread and didn't have the peak intensities experienced in Auckland. They had 50mm in one hour whereas we had 100mm fall over 24 hours.”

Over March 16-18 there was 136mm of rain recorded by MetService at the Tauranga Airport; 48.6mm Thursday, 55.6mm on the Friday and 32.4mm on the Saturday.

The week before from March 7-11 there was 179.4mm of rain in Tauranga over four days with the peak 67.2mm on March 8.

Since floods in April 2013 Tauranga City Council has changed its approach to city flooding, buying and removing flood prone Matua houses and significantly investing in the Mount Maunganui stormwater projects.

The council also voted to spend $10 million a year for three years on stormwater projects and computer modelling of the city's catchments. The capital works programme in the 2015 2025 is continuing at a rate of $6m per year.

“We have made some gradual improvements that have reduced low level, but frequent flooding in some areas, so last week's rain didn't cause the sort of problems that we might have seen in previous years,” says Wally.

“One of the more significant areas of improvement is in Matua where we've built a new overland flow path. That area is performing well and letting excess water drain away safely without incident. In previous heavy rain events, a lot of water would have flowed straight across a couple of private properties. It is always satisfying to see good designs working.”

The city council has also done a lot of improvement work in Totara, Maru and Te Maire streets. A bigger capacity stormwater system was installed along The Mall when the Pilot Bay boardwalk was constructed during 2013. This made a difference to previous flooding hotspots like Commons Avenue, although Wally says Commons Avenue is still going to face difficulties in larger rain events.

“The Mount Maunganui area sits quite low so tides have a major influence on the ability of the stormwater system to perform well because some of the outlets are submerged at high tide.

“Quite often people will see our reserves filling with water and call it flooding, but it's actually the stormwater system doing its job by giving the water a safe place to go until it can disperse.

“Places like Carmichael Reserve and the reserves along the Wairakei Stream and even open drains at the Otumoetai golf course are designed this way.”

Leaf litter is a real problem for stormwater inlets, says Wally. All 200 or so problem areas, are cleaned prior to a storm event and again afterwards.

“Residents can do their bit to protect their property by clearing gutters as much as possible during heavy rain. It all helps to maintain a resilient system and community,” says Wally.

More stormwater work will be undertaken in the Nikau Crescent area and the council has completed minor drainage improvements in Leinster Ave. Papamoa is well designed for major events with the exception of a couple of the older areas that rely on soakage alone, says Wally.



6 Comments

lol

Posted on 17-03-2017 19:30 | By Capt_Kaveman

like he said the rain was spread out over days and the ground was dry so most went there, but just wait heavy rain lack of drain clearing and the same will happen, a rain gauge in Papamoa recorded for the month of March from 1st to 13th = 404mm

Papamoaner

Posted on 17-03-2017 16:20 | By NZer

There are 2 spring tides every lunar month not everyday....

Well done TCC

Posted on 17-03-2017 12:19 | By Ron

The council has done an amazing amount of work over the last 20 years and should be congratulated. they get enough brickbats when they stuff up so the thing they do well should be congratulated. Well done TCC!

@Hot Stuff

Posted on 17-03-2017 12:17 | By morepork

I think you're being pessimistic. Of course it CAN flood because we can never limit what Nature throws at us, but the Council deserve credit for investing into the infrastructure and ensuring that what would PREVIOUSLY have been a tragic mess, wasn't this time. I was one of those who experienced the 2013 and previous floods and I have never forgotten the sinking feeling of watching the water rising to my house and being powerless to stop it. I had storm drains that exploded along the fenceline with my neighbour, there is a watermark on the bird bath in my front garden that shows a level where I could kayak around the lawn, and I had torrents of water racing through my garage. It was devastating (though others were much worse off) and I was distinctly nervous when the warnings were issued. This time, nothing. Well done, TCC!

@hotstuff

Posted on 17-03-2017 12:17 | By Papamoaner

Er, excuse me, there are two spring tides and two neap tides every day of the year. Many make the same mistake when talking about tides.

What a load of rubbish

Posted on 17-03-2017 09:10 | By Hot stuff

I've lived here a long time and it just depends on the conditions as to what floods in Tauranga . It can depend a lot on the tides , direction of the wind . Mark my words it will flood again when the conditions are right especially when the spring tides are here

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