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Retrieving Data

• Due to flood inflows during the week beginning Monday 27th March, Lake Matahina was full at the start of Friday 31st March.

• At Trustpower’s initiative, the process of lowering the lake level began on Friday 31st March in anticipation of forecast rain linked to Cyclone Debbie.

• The formal flood management process, in conjunction with the Bay of Plenty Regional Council (BOPRC), commenced on Tuesday 4 April when the lake was at 73.4m (11.30am), and then further lowered to 71.7m by Wednesday 5th April – being the minimum allowable limit in the resource consent.

• At the commencement of inflows arriving at the dam, BOPRC instructed Trustpower to release water to match inflows to retain storage in the lake in anticipation it would be required to attenuate the peak of the flood event.

• When flows further increased, BOPRC asked that Trustpower continue to release water within the limits of the downstream stop-bank capacity.

• Since 10.30pm on Wednesday 5th April to 5pm on Friday 7th April, inflows into the lake have exceeded outflows, i.e. lake storage has been utilised.

• This resulted in approximately twenty percent less water flowing down the river, during the peak of the flood than would have occurred if there were no dam in place.

• Overnight of 6th/7th April, discharge from the dam was progressively reduced – during this period inflows had also begun to reduce. Again inflows remained higher than outflows.

• At 9.30am on Friday 7th April, following discussions with BOPRC, outflows were reduced to 350 m3/s to allow BOPRC to safely access areas downstream for assessing flood damage. This reduced outflow was unsustainable due to storage constraints in the lake, and therefore in agreement with BOPRC flows were increased to 400m3/sec at 5pm Friday 7th April with a gradual reduction overnight. By 9am Saturday 8th April, outflows had been reduced to match inflows and the lake level was stabilising.

• In communications with BOPRC on the morning of Saturday 8th April, it was agreed inflows would match outflows and the situation would be reviewed later in the day.

• At 4.30pm on Saturday 8th April, discussions with Council agreed to continue current level of outflows through to next review meeting. This approach is mindful of the potential for rainfall next week, and aims to create lake storage availability.

• By 9am on Sunday 9th April, the lake inflows and outflows had dropped further. BOPRC confirmed current flows experienced downstream are not affecting them at all. Focus will remain on creating storage and achieving a lower lake level in advance of potential weather event coming.

• BOPRC were advised a spillway inspection is planned for Monday 10th April, which will require the discharge to be shut down for a short period – communication with BOPRC surrounding this will continue tomorrow. This activity will not impact the ability to drawdown to the lowest permitted level in advance of the next rainfall event.

• Planning continues for lake management over the weekend in collaboration with BOPRC.

• The flood management collaboration with BOPRC considers the vulnerability of the downstream population during night time hours. In this regard, Trustpower will continue to cooperate with BOPRC to manage releases to enable downstream inspection and works to be conducted safely.

• Our priority is always to keep the dam and the people below the dam safe.

 

For further information

• Whakatāne District Council Facebook: www.facebook.com/whakatanedistrictcouncil

• Bay of Plenty Emergency Management Civil Defence Facebook: www.facebook.com/bopcivildefence

• Bay of Plenty Regional Council Facebook: www.facebook.com/boprc  

• Listen to IXX FM: 90.5FM

• To report road closures, slips, stormwater and sewerage problems dial the Council on 306 0500

• To find the location of welfare centres dial the Council on 306 0500 or go on the Council’s website at www.whakatane.govt.nz or Facebook page www.facebook.com/whakatanedistrictcouncil