Stormwater catchpits, drains and pipes across Auckland during Tuesday’s heavy rain and subsequent flooding were at capacity, the council has said.
The state of emergency was declared on Tuesday as heavy rain overwhelmed parts of the city.
East Auckland woman Christina Teikamata told 1News yesterday a blocked drain caused the street she lives in to become a "lake".
She said once the drain was unblocked, the water receded within three minutes. "I never knew a blocked drain could do so much damage."
Teikamata said an Auckland Council representative turned up late on Tuesday, after she'd logged the incident.
"At 10pm a council truck came out and checked the drain. He said he had been all over Auckland that day as drains were blocked."
Doug Pirini, operations south team manager from Auckland Council’s healthy waters team, said the drain in Teikamata's street was, along with many others across the city, overwhelmed.
“Although it was logged as a blockage, the drains/catchpits were “full” or “at capacity” due to the volume of rain in the area, and like everywhere in Auckland the stormwater catchpits, drains and pipes in Bucklands Beach are built to cope with rainfall up to about 20mm per hour.
“Rainfall in excess of 20mm per hour (such as what we received on 9 May) will appear on the surface and activate our secondary system of floodplains and overland flowpaths which are required to accommodate rainfall events that exceed the primary system," he said.
Metservice meteorologist Peter Little said the highest measure of rainfall on Tuesday was logged at their site in Orewa, in Auckland’s north, between 11am and midday.
“In that one hour 49.5 was measured. Another station on Auckland’s North Shore, Ōkura, measured 48mm in the same time period."
He said the Orewa rainfall measure equated to 4900 litres of water per 100 square metres of land.
He said the bulk of the rain hit the city in that hour. “Eight stations had more than 40mm in an hour but the maximum was in Orewa."
“Almost every weather station had in excess of 20mm in one hour across the day."
He couldn’t comment on if the city’s stormwater system is fit for purpose but said given that amount of rainfall, “it would be very difficult to design a system that would cope".
“The pipes would have to be enormous.”
Pirini said prior to a forecast severe weather event, the council’s healthy waters department has, as part of its regular hotspot maintenance programme, begun clearing blocked inlets, outlets, catchpits and ponds that are known to contribute to flooding issues.
“A portion of these are high-risk and therefore included on the council’s regular ‘hot spot’ programme so are cleared before and after heavy rain.
“This was carried out ahead of this week’s weather event,” he said.
Auckland Mayor Wayne Brown ended the city's state of emergency this morning.
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