Last month’s heavy rain broke several long-standing records in some parts of the Coromandel, this month’s Environment Waikato Catchment Services Committee meeting heard.
While the Hikuai area recorded 900 mm falling over three days – a one in 150 year event, and half its usual annual rainfall - the existence of the Peninsula Project meant the Council was able to assist with river issues and follow up with landowners.
The intense event had significant consequences for localised areas. Natural Hazards Officer Adam Munro said the very high intensity event on May 18 and 19 flooded many parts of the Coromandel’s east coast. Many long-standing rainfall records were broken, and landowners who supplied information said May had been the wettest of any month on their records.
From January to April, Environment Waikato’s Pinnacles recorder received 634 mm of rain, but had 722 mm for May alone. Hamilton recorded 180 mm between January and April, and 166 mm in May. The event also came directly off the back of previous heavy rain 24 hours before in coastal areas and caused declarations of emergency at Tauranga and Matata.
NIWA had described the event as “phenomenal” and “unprecedented”, breaking records which began 95 years ago. A total of 789 homes were damaged in Tauranga alone and $50 million worth of damage had been recorded so far. NIWA scientists predicted larger, higher and more frequent floods each year in the Bay of Plenty, he said.
The west coast of the Coromandel was largely unaffected, and rivers such as the Tararu and Kauaeranga were only slightly affected. Flooding closed State Highway 25 at Whitianga, Hikuai and Whangamata and the Kopu-Hikuai road was also closed. Farmland was flooded, hills eroded, debris was swept down streams and several houses were inundated at Whangamata.
Work done last year under the Peninsula Project held up well, and staff were following up with work to clear streams so water would flow easily if another flood hit this winter. Planting and fencing was also being done to reduce the impact of flooding.
Staff were assessing the extent of the flood and the rainfall data would provide information for future planning.
Environment Waikato is working with Environment Bay of Plenty, Northland Regional Council and Auckland Regional Council on a joint project tracking major rainfall events. The study would identify areas most susceptible to increasingly high intensity events.
Cr Basil Morrison said the flood was not the first and would not be the last, and that changes could not continue to be addressed in an ad hoc way.
“I hope we will develop total catchment plans throughout the country with sub catchments included. There is more pressure to build on flood plains or earthquake-risk land, and the Peninsula Project is a classic example of how planning can work.
“The state has invested in existing schemes and there is a benefit to the state, and it should find the additional costs of maintaining these assets because of the public requirement for higher environmental standards. We haven’t actually seen the worst yet,” he said.