Exercise BayVac was held on Friday, 13 November 2009.
Based on a historial flood event, the scenario was devised to assist the Emergency Management Civil Defence staff of Hawke's Bay to test their emergency management systems.
Scenario
There was little rainfall over the district until 1st November. Then a series of fronts has pushed the annual rainfall above average for the month across the region, with particularly wet conditions in the Hastings district.
This heavy rain has resulted in moderate freshes in the rivers on the Heretaunga Plains and kept ground conditions wet over much of the remainder of Hawke’s Bay.
Early on Wednesday 11 November a heavy rain warning was received at HBRC from the Met Service. The HBRC Regional Council Duty Manager sent out a warning to all agencies on the HB Warning List. The warning advised a deepening low was moving down from the north and was expected to pass east of Northland and Bay of Plenty overnight to lie close to East Cape about dawn, then move past Gisborne and Hawke’s Bay during Wednesday/Thursday. Rainfall exceeding 80-120 mm was forecast for the 24 hours of the Thursday 12 November with possibly a similar amount in the following 24 hours. This depended on the track of the low.
Thursday 12 November
Rainfall alarms received at HBRC early morning for the Wairoa northern Hawke’s Bay area followed by further alarms north of Napier prior to 0700 hours.
The Nuhaka River reaches Green Alert Phase. Pukeorapa has received 50mm of rain and Wairoa 30mm
Napier has received 30 mm of rain, Hastings 25mm. A localised rainfall of 230 mm fell at Rissington and was continuing. 75 mm was recorded at Tutira.
Waipawa and Porangahau have received 60mm and 80mm respectively.
Rain continues throughout the whole district with localised high intensities.
At midday HBRC decide to activate their Emergency Operations Centre (EOC) to better manage the event. By late afternoon there is concern about reports of high intensity rainfall and the consequences.
Met Service Forecast the low responsible for the heavy rain was expected to continue to deepen to the east of the North Island, maintaining a strong easterly wind flow onto Hawke’s Bay. Coastal areas experienced periods of high intensity rainfall with steady rain continuing to fall in the Kaweka Ranges.
Severe Weather Warning – Exercise BayVac SEVERE WEATHER WARNING
ISSUED BY MetService AT 6.00 pm 12-Nov-2009 FORECAST:
‘THE HILL COUNTRY OF NORTHERN HAWKES BAY EAST OF NUHAKA, THE MAHIA PENINSULA, ALSO THE EASTERN HAWKES BAY HILL COUNTRY WEST OF NAPIER. In the 9 hours from 8pm today to 5 am Friday another 80mm100 mm possible with intensities possibly picking up to 10 mm per hours at times. The most likely area affected is from the eastern hill country of Hawke’s Bay west of Napier. Also 70 – 90 mm is expected over the Heretaunga Plains around Napier and Hastings”
Friday, 13 November
A significant amount of rain has fallen overnight in the Nuhaka catchment and the Nuhaka River has passed Red Alert and floodwaters are expected to escape from the channel flooding Nuhaka Township. The Wairoa River is at Orange Alert but early indications are that it won’t reach Red Alert although a further 100mm of rain has fallen in the past 24 hours and is continuing at the same intensity. Heavy rainfall is recorded from Whanawhana to Te Pohue. In Napier 70mm has fallen since midnight and 90mm in Hastings and is continuing at the same intensity. Rissington has recorded another 150mm in the past 12 hours. The Esk River is at Red Alert and indications are that 50 year levels could be reached. The Tutaekuri River is at Red Alert level and Ngaruroro River is at Orange Alert. The Tukituki and Waipawa Rivers are at Green Alert. The Awanui Stream and Karamu Stream are at Green Alert with areas of ponding appearing in the Upper Awanui Turamoe Road area. The Maraetotara River catchment has received over 80mm from 3am to 7am with rainfall intensities increasing. Reports of high intensity rainfall have just been received from Salisbury Road. Waipawa and Porangahau have received a further 100mm. The Mangaorapa rainfall station is recording rainfall intensities in excess of 25mm/hour. The Porangahau River is close to Orange Alert and indications are that Red Alert will be exceeded.
Severe Weather Warning – Exercise BayVac SEVERE WEATHER WARNING
ISSUED BY MetService AT 0800 13-Nov-2009 FORECAST:
Met Service new radar site at Mahia has located a band of high intensity rainfall (25 to 35mm/hour) moving in a NE direction from the Gwavas over Maraekakaho and will most likely exit off the coast at Awatoto. Predictions are that the effects will impact at Maraekakaho in about an hour then pass over Ohiti heading in a north easterly direction and reach southern Napier over the next 2 hours.
The exercise concluded at 3.30 pm on Friday, 13 November 2009.