The Otago Regional Council is continuing to closely monitor the deteriorating weather system around
Otago, with expectations there is likely to be some low-lying flooding of farmland in North Otago
catchments including the Kakanui River and the Gordon Road spillway along the Silver Stream near
Mosgiel may be triggered into action.
ORC’s Duty Flood Officer Eve Bruhns says the MetService has raised its prediction of rainfall in North Otago from yesterday, with the heavy rain warning from 1pm today for the following 21 hours expected to accumulate between 60mm-90mm of rain; with intensities up to about 15mm per hour.
“There’s still a lot of uncertainty around the extent of rain being expected,” Ms Bruhns says.
Rivers in North Otago such as the Kakanui River are expected to rise and flooding of some low-lying farmland inthe district is likely, she says.
The ORC’s Engineering Operations team are already on the ground monitoring the various ORC flood protection, drainage schemes and rivers, with no immediate concerns having been reported.
Ms Bruhns says a close watch is also being kept for coastal surges during high tides – at Port Chalmers about 2pm today and 2.30am tomorrow morning – saying any tide surges are unlikely, but could still be a “possibility” at this stage.
Given both the snow and heavy rainfall warnings for several parts of Otago, travellers should be considering whether or not to venture out on roads and to check the Waka Kotahi NZ Transport Agency web site for roading updates, Ms Bruhns says.
For North Otago, and other parts of Otago, the MetService now advises the rain is expected to fall as snow above 300 metres, lower than predictions yesterday, and heavy snow above 500 metres in some places.
On the Silver Stream catchment, ORC initial assessment indicates that there could be overflow at the Gordon Road spillway in the early hours of tomorrow morning.
This is an early assessment and the nature of the weather event makes it hard to predict accurately if and when the spillway will operate and the expected spilling amount, Ms Bruhns says.
If there is any escalation in the weather tonight, further notices and contact with residents will be made by Emergency Management Otago, with some residents located in the Gordon Road floodway area having already been contacted as a precautionary measure earlier today.
In Dunedin, there is not expected to be any overtopping of the Lindsay Creek channel in North East Valley or of the Water of Leith channel.
Peak flows on the Clutha River at Balclutha are not expected to go beyond 2000 cumecs.
The expected peak flow is significantly less than the peak observed in the February 2020 flood event.
“Flooding of low-lying areas adjacent to the river is likely but flows are expected to be well contained within the Lower Clutha Flood Protection and Drainage Scheme Floodbanks,” says Ms Bruhns.
She says the ORC’s drainage networks in West and East Taieri and Tokomairiro will likely be flowing “quite full”.
“Specific attention will be given by the ORC’s Flood Response Team to these areas and catchments as the predicted low could stall east of the South Island, resulting in further heavy rain,” Ms Bruhns says.
MetService predicts the low should move away to the east of the lower South Island by Wednesday. Rivers and lakes in Otago’s headwaters are not expected to rise, she says.
Background on Gordon Road spillway and floodway
The Gordon Road spillway is a lower section of the Silver Stream floodbank located on the true right bank between Gordon Road and Riccarton Road opposite the urban part of Mosgiel.
Media release: ORC monitoring waterways with heavy rain and snow expected