A Close Call for Tawa

A late evening deluge in Tawa yesterday caused some evacuations and was a close call for others. The Kenepuru Stream rose rapidly, and Tawa Weather recorded its wettest day since the weather station was commissioned in January 2005.

Wednesday 26 May 2010

Yesterday’s heavy rain event set a new record for the Tawa weather station when 80 mm of rain was recorded for the day – eclipsing the previous wettest day, the 20th of February 2009, when 54 mm of rain was recorded. The weather station was commissioned at the beginning of 2005, and conditions last night suggest it was Tawa’s heaviest rain event since the flash flood caused by the remnants of a tropical cyclone in January 2004.

Rain fell steadily for much of Tuesday, with 13mm recorded by 10:30 a.m., 17mm by 2:30 p.m. and 23mm by 6:30 p.m. Rain had peaked at 16 mm/hr at 3:36 p.m. before easing, but the rain rate suddenly increased around 6 o’clock in the evening.

At about 7 p.m. rain radar showed a band of heavy rain spiralling out of the weather system and across the south-western part of the North Island. Rain began falling more heavily in Tawa before suddenly intensifying and, in the hour to 8:55 p.m., 27 mm of rain fell – a new record for this year. Rainfall was so intense that it reached a rate of 95 mm per hour at 8:23 p.m.

The deluge coincided with high tide, making it more difficult for stormwater systems to cope. The Fire Service attended flooding in Court Road in Tawa, and some residents had to evacuate their homes. The Kenepuru Stream rose rapidly, but the flood management system installed at Glenside in the 1990s coped even though the Porirua Emergency Management Office reports that the stream exceeded its five-year flood level, flowing at about 50 cubic metres per second at the Porirua Town Centre. The stream’s ten-year flood level is 60 cubic metres per second at this location. Titahi Bay was isolated for a few hours and surface flooding was reported throughout the Tawa and Porirua areas.

Kenepuru Stream at Tawa 26 May 2010

Flattened grass in the Kenepuru Stream at Melville Street, Tawa marks the flood level reached during yesterday’s downpour.  [Click to view larger image]

By 9:10 p.m. the Tawa weather station had recorded 57 mm for the day, and the rain had fallen at a staggering rate of 109 mm/hr at 8:40 p.m. Rain continued at a high rate and 71 mm had been recorded by 10:15 p.m. Still the rain fell, reaching a total of 77 mm by eleven o’clock before it began easing.

The heavy rain event seems to have been quite localised with Tawa Weather recording 80 mm for the day and Redwood Weather, across the valley, recording 59 mm between 9 a.m. and midnight. The Linden weather station reported 88 mm with a peak rain rate of 38 mm/hr around 9 p.m. The Wellington Regional Council’s weather station at Grassleas Reserve in Tawa recorded 118.6 mm for the day with about 42 mm recorded in the hour around 9 p.m.

The council weather station at Seton Nossiter Park (Porirua catchment) recorded 87 mm, but other stations in the nearby area reported lower figures showing how concentrated the downpour was. Battle Hill, inland from Plimmerton, recorded 43.5 mm for the day, and Whenua Tapu (north of Paremata) reported 49 mm. This is confirmed by the private weather station at Mana which reported only 30 mm between 9 a.m. and midnight.

[ Compiled from data supplied by Linden Weather, Redwood Weather, the Greater Wellington Regional Council, the Porirua EMO website, and Tawa Weather. ]

3 Responses to “A Close Call for Tawa”

  1. Flying Deldas says:

    Certainly sounds like you would have had wet feet Kim. This weather is so up and down, but Gisborne was not too bad compared with what we headed off in early Monday morning.

  2. Andrew Gray says:

    This article refers to the Kenepuru stream but means the Porirua stream. The Kenepuru stream flows through Cannons Creek and is no where near Tawa.

  3. Ken says:

    Ooops. Thanks for pointing that out. We’ve been calling it the Kenepuru for years!

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