Lake filling fast after heat, rain

Okanagan Lake is filling up fast after a week of unseasonably hot weather followed by a rainy long weekend that triggered a flood warning for most of the B.C. Southern Interior.

The lake’s surface was measured at 342.28 metres above sea level as of Tuesday morning, up 80 centimetres in just two weeks, according to data from Environment Canada.

It left the lake just 20 cm below the full-pool mark at which operators try to hold it by adjusting the dam at the south end of the lake in Penticton.

“We’re not in trouble. Everything is OK,” said Shaun Reimer, who’s in charge of the dam’s operation, in a phone interview Tuesday morning.

Reimer had been aiming to reach the high-water mark near the end of June, but now expects it to arrive about three weeks earlier due to the rapid melt of the snowpack.

In the Okanagan, the snowpack was measured at 144% of normal on May 1, but had dipped to just 81% as of May 15, according to the B.C. River Forecast centre. In the Similkameen, the snowpack plunged from 91% of normal to 38% over the same period.

“So what we're trying to do is hold the rate of (lake) rise for a soft landing, but we're a little bit at the mercy of the weather,” said Reimer.

As of Tuesday morning, the dam was releasing approximately 35 cubic metres of water per second into Okanagan Lake, up from 10 just two weeks ago.

The dam’s outflow can safely go as high as 60 cubic metres per second, but there are downstream effects on fish habitat and private property to consider and Reimer said other tributaries to the Okanagan River are also swollen, making it a particularly delicate balance to strike this year.

“The one thing I can say with certainty is we are not getting into (something like) a 2017 (flood year) or anything like that,” said Reimer, who noted conditions then and in 2018 were vastly different with late-season snow accumulations.

Still, there’s enough of a risk that the B.C. River Forecast Centre on Monday issued a flood watch for the Okanagan, Thompson and Shuswap regions.

The warning was based in part on heavy rain in the forecast for Monday and Tuesday in some parts of the region.