August Flood Update to ELT

19 August 20101

MEMORANDUM

To: / Executive Leadership Team
From: / Roger Waugh
Bruce Crabbe / Date:Thursday 19 August 2010
Principal Technical Engineer
Operations Manager
Subject: / August 2010 flood event

Following is a brief report on the August 2010 flood event. This report briefly outlines the actions undertaken and results of those actions.

Situation on Friday 13 August 2010

Following Metservice reports of a significant rainfall forecast for the eastern Bay of Plenty for the weekend starting on Friday 13 August, the flood team was activated to ensure systems and people were available to deal with any issues that might have arisen.

MetService was predicting up to 280mm of rain in the ranges and up to 130mm rain in coastal areas. This was expected to occur from 6pm Friday through until 3am Sunday. Additionally MetService is warning of heavy northerly swells at sea that will cause some very high tides over the next few days, particularly as there are spring tides occurring currently as well.

Staff were liaising with TrustPower regarding the Matahina Dam on the RangitāikiRiver to ensure it had maximum available storage capacity to collect floodwaters.

Council staff advised landowners with stock on low paddocks near rivers and streams to move them to higher ground before nightfall. Council also advised people in low areas near rivers, streams and coastal areas that they should be cautious and remain vigilant due to the expected rain and the high tide periods.

A media release was issued and Council’s website updated to relay this information to the public.

Situation on Saturday 14 August 2010

First situation report was issued at 5am, with further ones at 8am, 1pm, 4,30pm, 7.30pm, 9pm and 11.30pm. Media and the website were updated based on information received in each of this situation reports.

Metservice forecast was in the 18 hours from 6pm Saturday to midday Sunday that we should expect 120mm to 180mm in the ranges, and 60mm to 110mm about lower lying areas. Peak intensities reaching 25mm to 35mm per hour were possible. Rainfall was expected to be most intense around midnight.

At this stage the Otara, Waioeka, Waimana Rivers had peakedandstarted to recede.

Stoplogs were being installed at the WhakatāneWharf and Fishing Club sites in preparation for the river continuing to rise and the sea swell approaching. High tidehad passed about 11pm.

Operation crews were out monitoring pumps and stopbanks and responding to calls as needed. Trust Powercontinuing to spill with overall spilling andgeneration at approx 300m3/secand spill of 300 m3/s.MatahinaLake levels were declining slowly toward their minimum operating level.

Due to many large slips the Waioeka gorge was closed, and Opotiki was isolated due to slips in surrounding areas. The road was also closed between Tāneatua and Kutarere by flooding.

Situation on Sunday 15 August 2010

Situation reports were issued at 2am, 4.30am, 10.30am, 2pm, 5pm, 7pm and 10.30pm. Media and the website were updated based on information received in each of this situation reports and included some additional releases.

By mid-morning the rainfall was easing across the region. Trust Power had responded well by lowering Matahina lake levels with increased spilling to a total generation and spill of 300 m3/s

The Otara, Waioeka, and WaimanaRivers previously exceeded second warning levels, but were now receding. The Whakatāne River flow reached 2200m3/s, which was approximately a 30-year return period flow and it was still of concern. Businesses on the Whakatāne wharf were given warnings as the river reached the wharf level. Whakatāne District Council had a digger lower the spit level in difficult conditions.

Stop logs were installed due to rising levels in the WhakatāneRiver, and also in the Te Rahu and WaiohoCanals. High tide was expected around 11am.

The most significant issue for operation staff was that the Te Rahu stopbank had breached during the morning and staff and contractors were on site doing emergency work to repair the stopbank. The breach was repaired by night fall and staff continued to monitor the site for seepage. Whakatane District Council (Eastern Bay of Plenty Civil Defence) managed evacuations in the Fortunes Road area as a result of the stopbank breach.

In addition to our pumping stations, pumps had been brought in from other areas to help clear flood waters from the land as river levels continued to drop. Operation staff and contractors continued to monitor pumps and stopbanks and respond to calls as needed.

There are a number of road closures around the region from flood waters and land slips and Council tried to update media and redirect them to Whakatane District Council and New Zealand Transport Agency websites for this information.

Situation on Monday 16 August 2010

Situation reports were issued at 6am and 3pm. Media and the website were updated based on information received in each of these situation reports.

No additional problems were reported overnight and we had eight emergency pumps in the Fortunes Road basin that had been running through the night to help clear water. Levels in the WhakataneRiverhad dropped enough for the Kope Orini floodgates to open at about 3am.

LakeMatahina had reached maximum normal operating level, Trustpower had increased spilling to 340 m3/s to maintain this level. Inflows were 330 m3/s, down from their overnight peak of 350 m3/s.

Other that the WhakataneRiver, all other river levels were continuing to receed. Stoplogs around the WhakataneWharfwere removed. Additional pumping was deployed in order of priority to areas where requests had been made.

A controlled breach was undertaken of the Whakatāne rural stopbank at the request of the farmer (Mr Nathan Jones) in consultation with our staff and using our equipment. Repair work continued on the Te Rahu stopbank to strengthen it.

Situation since Monday 16 August 2010

Pumps have continued to run at priority sites. Further work has continued at Te Rahu stopbank and Mr Jones’ farm.

Staff have continued to monitor the pumps and situation and have been undertaking site visits to assess damage to stopbanks and other infrastructure.

Daily media releases have been issued and put onto our website. Additionally, navigational safety warnings were incorporated into media releases.

Many roads re-opened on Monday and Tuesday.

Rainfall statistical information

The event was not that notable in terms of rainfall in isolation with a maximum of five year to 10 year return type events. However there has beensignificant rainfall totals for August so far. Compared to historical data for August, the totals we recorded are the highest on record for a number of sites in the eastern catchments. This is on top of a relatively wet July for some of the catchments. Below are some of the sites.

Some catchments are likely to register their highest winter rainfall since records began, for example, Otara at ŌpōtikiWharf.

Effectiveness of Flood Warning Procedures and Response

Seven families were evacuated in the Fortunes Road basin due to the breach on the Te Rahu Canal. This evacuation was managed by Whakatāne District Council Emergency Operations Centre following advice from Regional Council Flood Managers.

No report of homes being flooded across the Eastern Bay of Plenty. Some garages were flooded due to localised drainage problems.

No stock losses have been reported. Farmers acted on warnings early and moved stock to higher ground.

Additional pumping was brought into the area early and deployed as soon as appropriate. A controlled cut was undertaken where water was trapped behind low level rural stopbanks on the WhakatāneRiver. By Wednesday most flood water had been removed with the confidence that grasses will recover in areas where silt is not too deep.

Staff Involvement

Staff worked long hours over the weekend, the flood room was operational through to 11:00pm Sunday 15th. Flood managers continued to monitor rivers and take calls through until Thurday 19th.

Operations staff maintained a 24 hour operations through the event until emergency pumping was completed.

Communications staff supported the flood management team with media management and support following the event with updates and reports.

In addition to sending out the media releases to our regional and national media lists and updating our website, the releases were also sent to the Council Communications Managers within our region, our Councillor and Chairman, our local Members of Parliament and the Executive Leadership Team.

Media that we took calls from and managed directly during the event or we have monitored as running stories since included:

TV One news

TV3 news

Maori TV news

Prime News

Radio New Zealand

Newstalk ZB

Radio Live

Media Works (various stations)

Radio Network (various stations)

One Double X

New Zealand Herald

Dominion Post

Sunday Star Times

Bay of Plenty Times

Whakatane Beacon

Eastern Bay News

New Zealand Press Association

Scoop.co

Stuff.co

Flood Damage

In the coming week, staff will undertake a comprehensive inspection of all river and drainage systems to assess flood damage to quantify the cost to repair. At this stage it is too early to indicate any indication of cost.

Potential Future Discussion

Discussion in the community and media could take place around a number of issues as a result of the weekend flood event. Potential negative topics (perceived or otherwise) could include:

  • Why the breach in the Te Rahu occurred
  • The Whakatāne spilt fuse and action/inaction taken by Whakatāne Distict Council. This function of the fuse continues to be a point of debate.
  • Flooding of properties upstream of LakeAniwhenua and the actions taken by Bay of Plenty Energy during the event. Discussion from the community of the long term management of the lake delta will continue.
  • Inaction by authorities where flooding has occurred to garages in the Onepū area.

August Flood Update to ELT

19 August 20101

Site Name / Rainfall 1-17 August / Rainfall 1-17 August compared to historical rainfall for month of August / Rainfall 13-15 August / Rainfall 13-15 August Return Period / PeakRiver Height / PeakRiver Flow / Peak Flow Return Period
(mm) / (mm) / (years) / (m) / (m3/s) / (years)
Waipapa at Goodalls / 321 / 152 / <2yr
TaurangaHarbour at Omokoroa / 170 / 63 / <2yr
Rapurapu at Kaimai Summit / 180 / 95 / <2yr
Kaituna at Te Matai / 205 / 94 / <2yr / 3.31 / 128 / <5 yr
Rotorua at Whakarewarewa / 266 / 106 / <2yr
Rotorua at Kaharoa / 364 / 163 / 2yr
Mangorewa at Saunders / 395 / 216 / 5yr / 3.83 / 108 / <5 yr
Pongakawa / 321 / 146 / 2yr
Ohinekoao at Herepuru Road / 322 / 142
Tarawera at Awakaponga / 281 / 115 / 2yr / 2.26 / 60
Rangitaiki at Thornton / 194 / 72 / <2yr
Rangitaiki at Te Teko / 215 / 98 / <2yr / 4.57 / 375 / 5-10yr
Rangitaiki at Waihua / 304 / 129 / <2yr
Whirinaki at Galatea / 213 / 73 / <2yr
Rangitaiki at Kokomoka / 202 / 86 / <2yr
Whakatane at Huiarau Summit / 291 / 176 / 2-5yr
Whakatane at Huitieke / 402 / Highest since records began - 1978 / 199 / 5-10yr
Waimana at Ranger Station / 766 / 338 / 10yr / 4.39 / 280 / 5yr
Whakatane at Kopeopeo / 209
Whakatāne at Valley Road / 7.15 / 2174 / 30yr
Whakatane at Wharf / 2.3
Waioeka at Koranga / 403 / Highest since records began - 1985 / 190 / <2yr
Waioeka at Cableway / 658 / Highest since records began - 1990 / 256 / 2-5yr / 6.74 / 799 / <5 yr
Waioeka at Mouth of Gorge / 426 / 176 / 5-10yr
Otara at Tutaetoko / 589 / Highest since records began - 1990 / 242 / 5-10yr
Otara at BrownsBridge / 452 / Highest since records began - 1990 / 187 / 5-10yr / 4.29 / 430 / 5yr
Otara at OpotikiTownWharf / 275 / Highest since records began - 1995 / 104 / <2yr
Pakihi at Pakihi Station / 726 / Highest since records began - 1990 / 274 / 5-10yr
Pakihi at Rakanui / 428 / Highest since records began - 1991 / 166 / 2-5yr
Haparapara at East Cape / 1023 / Highest since records began - 1997 / 345 / 2yr