Thursday, August 18, 2022

Big cleanup after rains dump 200mm in two days

Neal Wallace
Roads, bridges and homes affected by deluge.
The Ashburton River has breached its banks, flooding surrounding farmland. Photo: Ashburton District Council/Facebook

Rural communities in inland parts of Otago and Canterbury were cleaning up today after more than 200mm of rain fell over two days this week, flooding homes, washing out bridges and damaging roads.

The headwaters of Otago and Canterbury lakes and rivers have borne the brunt of the storm, with Mt Cook recording its wettest July in 100 years with 583mm falling so far, of which 422mm fell on Monday and Tuesday.

A washed-out bridge has isolated the Lake Ohau community and flooded parts of Omarama and Otematata.

High flows generated in the headwaters of the Mataura River have closed some roads including in Gore.

The Ashburton River has breached its banks, flooding surrounding farmland.

Environment Canterbury reports that the Rangitata, Orari, Lower Waitaki, Rakaia and Waimakariri Rivers are all being closely monitored.

While flows are high, they believe they will be contained within the river systems.

The Manuherikia River in Central Otago peaked just below 600 cumecs, its third highest flow since 1971.

Eastern areas received less than 10mm, but the Otago Regional Council is warning the heavy rain has increased river flows, which could flood areas downstream.

The council’s natural hazards manager, Jean-Luc Payan, warned that Contact Energy has already increased Roxburgh Dam outflows into the Clutha River to 1,400 cumecs and expects to increase that further today to between 1,500 and 1,600 cumecs. 

With inflows from other rivers, this could increase the Clutha River flow downstream to between 1,700 and 1,800 cumecs.

“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,” he says.

“This includes the Aero Club area, upper Inch Clutha, and railway reserve land.” 

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