As more inclement weather closes in on Taranaki, figures showing the staggering water flows in the province's rivers triggered by the storm event last week are a stark reminder of how fast rivers and streams can rise.
The torrential rain at the beginning of July saw many rivers hit incredible maximum flows, including 417m³/sec in the Waiwhakaiho River at Egmont Village and 1367m³/sec in the Waitara River at Bertrand Road.
Taranaki Regional Council figures show flooding at the Tāngāhoe River in South Taranaki was a one-in-20-year event (with 349m³/sec maximum flow) and the Waitōtara River experienced a one-in-11-year flood when Taranaki was deluged by a huge amount of rain on 3 and 4 July.
Flooding in the Waiongana Stream on SH3A had an annual exceedance probability of 2.8 percent, making it a one-in-36-year event with a 194m³/sec maximum river flow.
A river last week. Photo: Taranaki Regional Council
The monitoring station at the Waiwhakaiho River at Egmont Village recorded 161mm in 12 hours on 3 July as many rivers and streams flooded and the public were urged to stay home and avoid unnecessary travel as roads were inundated with surface water.
Council Operations Director Daniel Harrison said the weather events were a stark reminder for the public to be aware of how fast rivers and streams could rise.
"The stats from early July are staggering as Taranaki was hit by huge downpours caused by thunderstorms with many waterways experiencing very rare flooding events.
"We've prepared for this with our management of flood defences in Waitara and at the lower Waiwhakaiho River and it was extremely pleasing to see how well the schemes worked given the huge volume of water in those rivers.
Harrison said Taranaki was a great place to live but severe weather events needed to be respected.
"We live in a fantastic part of the world but it's fair to say the environment is extremely dynamic and things can change very quickly so please always be aware of the dangers from flooding and have a plan to get to safety if the rivers rise fast."
The regional council provided information to Taranaki Civil Defence Emergency Management (CDEM) about rainfall and river flows during weather events, and alerts were issued by CDEM to the public with support from the TRCl via its communication channels.
Other notable weather stats from last week include:
- The TRC's gauge on the Mangaehu River in East Taranaki recorded a maximum flow of 323.351m³/sec.
- The Waitara River gauge at the Pūrangi Bridge recorded 580m³/sec.
- The Tāngāhoe River maximum flow of 348.906m³/sec was well above the mean average flood of 164.302m³/sec (although records only date from 2018).
- The upper catchment flow site on the Waitōtara River (at Rimunui Station) recorded a peak water level of 12.5m (418m³/sec) at 11pm on 3 July.
- Brooklands Zoo recorded the most rain in a 12-hour period at 126.4mm since records at the site began in 2011.
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