1 in 20 year rainfall for south Wellington

Regional deluge from ex-cyclone Debbie

Rain gauges operated by Greater Wellington detail the extent that rainfall brought by the ex-cyclone Debbie had over the region.

Just to hand

1 in 20 year rainfall for south Wellington

Parts of Wellington, Porirua and Hutt cities were hit with very intense rainfall over night on 5th April.

Berhampore was inundated with 75mm of rain over just a six hour period and 94mm over 12 hours. The average rainfall for April is around 90mm. This was very intense rainfall and is estimated to be in excess of a 1 in 20-year return period. Just over the hill from this rain gauge, the Owhiro Stream raged and caused flooding problems.

In other parts of the city rainfall totals over 12 hours of 64mm at Hataitai, 74mm at Te Papa, 66mm at Khandallah, 61mm at Karori Reservoir and 91mm at Woodridge were recorded.

Many urban streams were flowing high and surface flooding occurred in numerous places. The peak flow in the Porirua Stream reached a level expected once every year.

1 in 10 year rainfall for Masterton

Rainfall started in the Wairarapa and eastern hills on Monday 3rd April and persisted for three days.

While no really intense downpours occurred the total rainfall over the 3 day period has been significant with Masterton receiving 136mm which is twice the average expected for the entire month of April. This is estimated to be a 1 in 10-year rainfall event for the town.

Elsewhere in the Wairarapa rainfall totals of 167mm, 147mm and 111mm where recorded over the three days at Tanawa Hut (north of Tinui), Mauriceville (north of Masterton) and Tauherenikau (Featherston).

The Ruamahanga River peaked at 6.45am on the morning of 6th April with an estimated flow rate of 1000 cubic metres per second going under the Waihenga/Martinborough Bridge and through the Jenkins Dip floodway. A flood flow of this magnitude is expected to occur once in every two years.

The Tararua Range has not received heavy rainfall during the event so the Ruamahanga River has been spared any additional flood runoff adding to the already high flows.

The rainfall over the Wairarapa area will be welcome to many farmers and land owners with farm dams filling up and the rainfall deficit being erased or at least decreased.

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