Due to the heavy rain forecast this week, the Matahina dam water level has been dropped to its lowest level ever recorded as a precaution.

With another deluge expected in the coming days, Bay of Plenty Regional Council duty flood manager Peter Blackwood says a number of precautions are being taken in the Edgecumbe area.

'Our pumps along the Rangitaiki are also going full speed to remove water from flooded areas and there are ongoing inspections of the stop banks. Our pumps in the lower Kaituna have also been going flat tack.

'Outside of the eastern bay, the Okere gates have been open for more than two weeks and are discharging flood water from Lakes Rotoiti and Rotorua at capacity. There are no further steps we can take to lower these lake levels and residents should expect some flooding around lake margins."

MetService's weather warning issued today is for 200-250mm of rain over the 48 hours from noon Wednesday until noon Friday.

'With the information we currently have available, the bulk of the rain is going to arrive Thursday and it looks like coastal communities are going to be hit the worst. Severe gales are also predicted along the coast which will likely lead to storm surges and flooding of coastal margins.

'We will know more by the end of today and will send another update then. We will also issue regular updates in the lead up to this weather,” says Peter.

STATE OF EMERGENCY DECLARED:

The Bay of Plenty Civil Defence Emergency Management Group has declared a new local state of emergency due to the expected arrival of Cyclone Cook in the next 48 hours and the current Severe Weather Warning.

This supersedes the state of Emergency declared for the Whakatane District Council last Thursday.

The Bay of Plenty is forecast to receive 200 to 250mm of rain in the 48 hours from midday Wednesday. The region is already dealing with the effects of Ex-Cyclone Debbie which saw extensive rain fall in the region last week.

The declaration means that there will be a regional coordination of Civil Defence Emergency Management preparedness and response.

Residents are urged to keep up to date with the latest weather updates and take heed of any warnings.

People can sign up for Bay of Plenty Civil Defence text alerts by texting the two letters for your area where you live to 2028:

• TA – Tauranga
• WB – Western Bay
• KA – Kawerau
• WH – Whakatāne
• RO – Rotorua
• OP – Ōpōtiki

People can also follow the Bay of Plenty Civil Defence Facebook page at www.facebook.com/bopcivildefence or visit the Bay of Plenty Civil Defence website at www.bopcivildefence.govt.nz for information about how to get ready before an event.

'ONE IN 500 YEAR EVENT'

Last week's rain from cyclone Debbie is being called a one in 500 year event, and offered as an explanation for the collapse of the concrete floodwall that resulted in 1600 people from Edgecumbe having to be evacuated.

It is the second one-in-500-year rainfall event in 22 years. The May 2005 the debris flow in Matata where more than 700,000 cubic metres of debris destroyed more than 100 homes was also ascribed to a rainfall event with a return period of 200 to 500 years and rainfall intensities of greater than 2mm/minute.

In July 2004, there were three days of heavy rain dumped on an already saturated catchment, leading to failed stopbanks and widespread flooding. Edgecumbe escaped the worst but large tracts of rural land and low-lying settlements were inundated. There were more floods in 2005, 2007, and in 2013.

The 2004 flood resulted in 17,000 people facing drinking water shortages, 3200 homes were evacuated, 450 farms and orchards were damaged and the Rangitaiki burst its banks in a 1-in-100 year flood. At Opotiki, there was 280mm of rainfall in 48 hours, similar to rainfall levels forecast for this week.

The Rangitaiki plains, a former swamp, have always been floodprone, but this was made worse by the 1987 Edgecumbe earthquake which dropped some parts of the town and adjacent rural land by up to two metres.

Areas that before 1987 drained by gravity now have to be pumped. In flood, the Rangitaiki River runs higher than Edgecumbe's ground level – a situation that makes it difficult to safely manage stormwater in heavy rains.

The gap in the floodwall that breached last week has been plugged and no more water is flowing from the river into Edgecumbe. Construction work is continuing in this are today.

Because of the volume that needs to be pumped out following last week's flood, it is expected to take another week to 10 days to complete.

The water is now naturally receding; however because of the volume more will need to be pumped out. Bay of Plenty Regional Council has begun pumping and this could take 7-10 days to complete – and the rain begins again before then.

The Edgecumbe township remains cordoned off to ensure public safety while pumping is in progress and to protect people from sanitation risks associated with sewage system failures and surface water contamination., says a statement from the Bay of Plenty Regional Council today.

Due to the risk of contamination from flood waters, there is a boil water notice in effect for Tanuatua, Ruatoki and Rangitaiki Plains.