‘Phenomenal’ rain tops lake
Opuha Water Ltd chief executive Tony McCormick is not going to forget last Friday’s south-easterly storm in a hurry.
One-quarter of the annual rainfall for South Canterbury fell in less than a day into the catchment of Lake Opuha causing all sorts of headaches for the dam management.
‘‘We had 150mm in 10 hours that’s pretty phenomenal and to be honest, we were very concerned as we had been running the lake very full.
‘‘For about three hours through Friday afternoon, we were seeing about 280 cubic metres per second coming into the dam. That’s a lot of water for us as the spillway capacity is only 300 cumecs and the lake was still rising.
‘‘Then at about 8pm on Friday, we detected it had peaked. This was the reprieve we wanted. At about 10pm on Friday we realised we were going to be okay.
‘‘It certainly concerned us, and we were in touch with Ecan flood control. We were monitoring it through the night but were never at the point of triggering any emergency.’’
The lake level continued to rise through Saturday but in small increments, McCormick said. It was now spilling about 70 cumecs. There will be some work to do downstream with irrigation schemes as there has been surface runoff into the water races.
Since the downstream weir upgrade, they were confident in dealing with large flows, McCormick said.
‘‘We have been holding the lake higher than normal. We are still a bit gun-shy from the last two dry seasons and reviewing our operating regime.
‘‘It’s been an extreme event, and it has shown us some things that we can do better.’’
McCormick said the public perception that the dam added to the flooded Opihi River which peaked at 1500 cumecs at Pleasant Point was unjustified. Without the dam withholding water the flow could have reached 1800 cumecs, he said
The storm also created stress for South Canterbury farmers.
Federated Farmers provincial president Mark Adams who farms at Fairlie said the storm was a one in 10-year event. ‘‘We had 90 millimetres over 32 hours, and water started running from the first drop because the ground was already saturated. That’s what’s made it so damaging,’’ he said.
Adams said farmers ‘‘out on the coast’’ would have copped more ran because it ‘‘just slammed in.’’
‘‘The low lying dairy guys are the ones who will be struggling because they will be calving whereas the production season for sheep and beef doesn’t start until September.
‘‘There will be some logistical issues for the guys who are trying to milk cows and have cows coming home. They will be out on grazing and graziers will be wanting them off, and the dairy farmers will want them to stay where they are. There is going to be some tension there.’’
Beef+Lamb New Zealand farmer-director Bill Wright, from Cannondale, said he had got off lightly with only 37mm of rain. But farms only 10 kilometres away collected 100mm.
‘‘The stock are sick of it,’’ he said.
‘‘That’s the harsh bit, and farmers are making decisions now on where to put the stock and trying to find dry paddocks, and it is getting difficult.
‘‘It’s not ideal having stock in mud, either environmentally for the soil or the people shifting the breaks. But we are well forecasted now for these events, and with modern farming techniques, it’s not out of control.
‘‘It’s the cleanup and the aftermath and whether it affects the livestock and production - that is the problem.’’