Tuesday 19 July 2022
Residents near Inch Clutha downstream of Balclutha and Ophir township on the banks of the Manuherekia River are being advised to keep a sharp watch on river levels, respectively the Clutha and Manuherekia Rivers.
5.30pm 19 July 2022
Otago Regional Council Manager Natural Hazards, Jean-Luc Payan, says unprotected low lying areas of Inch Clutha and Ophir should expect some mainly, low-lying farmland flooding from the rising rivers.
Dr Payan says around the lower Clutha district, Contact Energy had increased the Roxburgh Dam outflows to 1400 cumecs this morning, and they were expected to rise further this afternoon to 1500-1600 cumecs.
“Based on the expected flood travel time of approximately 15 hours from Roxburgh to Balclutha, the river flows at Balclutha may peak later tomorrow morning,” Dr Payan says.
The flow peak at Balclutha could be in the range 1700-1800 cumecs, based on predicted Roxburgh outflows plus the contribution also from the Pomahaka River and other tributaries, Dr Payan says.
“Flows at this range may cause flooding of low-lying areas adjacent to the river upstream of Balclutha as well as unprotected areas on the lower Clutha River Delta. This includes the Aero Club area, upper Inch Clutha, and railway reserve land,” he says.
MetService says the complex low pressure system over New Zealand is expected to move eastwards tomorrow (Thursday) allowing a ridge of high pressure to build over the country on Friday and Saturday.
The highest previous flow recorded for the Manuherekia River at Ophir, since 1971, was 602 cumecs in December 1995, and today’s event is likely to be around the third highest flow, below 600 cumecs.
“Flooding of land adjacent to the Manuherekia River, mainly farmland, is expected in addition to localised bank erosion,” he says.
He says the Manuherekia River at Ophir had reached its peak around 4pm today, and while high, was now beginning to fall.
“People should still stay away from any rivers at present,” Dr Payan cautioned.
Downstream, the Manuherekia River at Alexandra was due to peak there overnight.
Roading closures and updates for Otago are available from Waka Kotahi NZ Transport Agency’s website.
Dr Payan says the rivers in the Lake Wakatipu area; the Dart, Rees and Shotover, and Lake Wanaka rivers; Matukituki and Wilkin and the Lake Hawea catchments are expected to all have peaked overnight and be receding.
Dr Payan says rainfall around North Otago was “low intensity”, around less than 2.5 mm per hour, with rain gauges in the Kakanui, Kauru and Shag catchments having recorded 12mm-20mm.
Young River dam under watch, but lake level falling
Dr Payan says the level of the 2 kilometre long lake on Young River had risen about 2 metres from the recent rainfall, but was on its way back down (as at 5pm today).
He described the 2 metre rise as “not uncommon or unusual”; based on historic data.
“Yes, we’re keeping a close eye on rainfalls and water levels at the dam,” says Dr Payan.
Since the natural landslide which dammed the Young River in 2007, ORC has installed a remote water level recorder and also a rain gauge, which captures lake rises and falls as well as rainfall within that catchment.
Dr Payan emphasized people should take note that the Department of Conservation has issued a “code red” on the Young Valley, meaning public access is closed until further notice.
Data from both recorders is available on the ORC’s web site, in the Upper Clutha section of the Water Monitoring and Alert section.
Young River at Landslide - Rainfall
Young River at Landslide - Water Level
9.30am 19 July 2022
The Otago Regional Council is urging people to be cautious around rivers and low lying land as waterways around Central Otago and the upper Clutha catchments rise with the on-going rain system.
ORC’s Manager Natural Hazards Jean-Luc Payan says the river levels in the Upper Clutha and Central Otago catchments have risen during the night and are expected to stay high during the day.
“Caution is required for activities near river banks or low lying land adjacent to rivers,” Dr Payan says.
Heavy rain has fallen in the headwaters of Otago; in the Upper Clutha River catchments and in the headwaters of Central Otago rivers, including but not limited to the Kawarau River, the Shotover River, the Lindis River, the Manuherekia River and the Kye Burn/Upper Taieri River, he says.
“River levels in those catchments have risen during the night and expected to stay high during the day. This includes the downstream sections of rivers as higher than normal flows will result from the heavy rain in the headwaters,” Dr Payan says.
He urges people with concerns to visit the water monitoring and alerts page.
MetService says there remains an active front affecting southern New Zealand which stays slow-moving today (Tuesday) as a few low centres form on the front, which then evolves into a complex low pressure system late today and tomorrow.
This system should then move slowly eastwards on Thursday, bringing strong and cold southerlies to the east of New Zealand. A ridge is forecast to build over the South Island on Friday and Saturday.
No flooding is expected for Lake Wakatipu and Lake Wanaka; lake reserves are likely to inundate.
The Manuherekia River at Ophir went through its second alarm at 200 cumecs.
The river is expected to peak later today.
The Lindis River catchment is also experiencing high flows.