Flooding concern in Okanagan Lake brings 'aggressive schedule of releases' from the Penticton Dam

A high snowpack level report has Penticton’s dam manager lowering Okanagan lake levels in anticipation of an elevated risk of flooding when the spring melt occurs.

The BC River Forecast Centre published its monthly snow survey Wednesday, reporting several snowpacks much deeper than average.

“Going back to the February first snow bulletin, that was high as well. So at that point, we started a much more sort of aggressive schedule of releases from Okanagan Lake Dam, so that we increased our outflow in anticipation of a higher than normal runoff, ” Shaun Reimer, the Okanagan section head and Penticton dam manager said.

“The lake started lowering much more quickly than it had been up to that point and we've continued to do that now, certainly in the face of this higher, even the previous month, the snowbasin index that we're seeing here in the Okanagan.”

Last year, a cool spring delayed the snowmelt, and heavy rainfall caused creeks and rivers to swell, issuing flood warnings across the interior. In 2021, the Okanagan saw an incredibly dry spring and summer and the low lake levels brought on a drought.

“We're about 10 centimetres lower on the lake than we were last year. So we have a little bit more room to work with, which is comforting from my perspective in terms of managing the flows at the lake level. But in a strange way, over the last three years, it all comes down to what happens in June. And unfortunately, we've had some extremes in the last three years.”

The latest snowpack data shows most regions in the Okanagan have snow depths at 124 per cent of normal.

“Like always, the high snowpack doesn't guarantee flooding, but it increases the possibility [and] the probability of flooding will occur. I think in terms of volume flooding, which is what we typically deal with on the lake, we're in a fairly good position to absorb a lot of that water,” Reimer said.

“We still have a lot of winter to go. Typically we're going to be building up snow in the hills for another month before we sort of peak here in the Okanagan. So there's still a lot of time for things and conditions to change.”

He added that Okanagan Lake has been sitting well below the full pool target level throughout most of the winter.

“We kind of entered into the season below normal. But again, after our February forecast, we made sure that we kept that going and dropping the lake in anticipation of a big runoff.”

The main areas of concern are those that were hit by the catastrophic flooding that occurred in November 2021.

“Due to the significant erosion and possible changes in river channel morphology that occurred within many areas (including but not limited to the Coldwater River, Nicola River, Tulameen River, Coquihalla River and lower Fraser River), rivers may be at increased vulnerability to high flows at lower levels than previous freshet seasons," the forecast centre said.

“Typically, if you've been impacted in the past, that's a great indicator that it's something to think about and always be prepared for. Some of those rivers were particularly impacted by that November event a couple of years ago," Reimer added.

Recommendations to prepare by paying attention to the weather forecasts for a heatwave through the freshet period or significant rainfall events, if you’re in an area close to creeks, or floodplains.

Reimer’s main focus remains on the area around the Okanagan river, but he also pays attention to other streams that could impact it.

The difficulty remains that managing spring freshet all hinges on the upcoming weather.

“It is almost impossible to deal with any sort of extreme conditions. We try to work on models that give us certain information, but they're imperfect. And no hydrologic model that can give us an info forecast, or tell us where a lake level will be, is going to deal with extreme conditions,” Reimer said.

“It's all coming down to what is going to happen in June, to let us know where we're going to end up at the end of the day.”