In the midst of a sudden flood on the weekend, the Regional District of Central Kootenay (RDCK) issued evacuation orders for hundreds of households in the Duhamel and Crawford Creek drainages, in the Ymir-Salmo area, the Slocan Valley, and the Broadwater Road area of Robson.
All these orders were rescinded within 24 hours because water levels lowered, but there is still danger including “contaminated flood water, debris, and riverbanks either undermined or undercut,” says Chris Johnson, the RDCK’s emergency operations manager.
During and following the storm, water was coming down Duhamel Creek at 19 cubic metres per second.
“We get nervous if it goes above 10 cubic metres,” says Johnson. “We would be checking it a couple of times a day. And this was double that.”
The weather had been hot the previous week, so the creek and ground were already full of snowmelt by the time the sudden rain hit.
“Without the snowmelt there would have been more capacity and the rain might not have been much of an issue,” Johnson says. “Even if we had gotten the same amount of rain over 48 hours, it might have been better. But that storm was travelling at 70 km/h.”
Snowmelt typically enters a creek gradually, giving emergency managers time to predict its effects. But Johnson says heavy rainfall will travel from the top to bottom of steep creeks like Duhamel and Crawford in two to three hours.
“When you look at Crawford Creek,” Johnson says, “it goes way back into the Purcells, and there’s a lot of alpine with a lot of snow still out there. We looked at risk and then talked with the subject matter experts from water stewardship from the province.”
Exacerbating the risk was the existence of “orphan dikes” found on both creeks.
Decades ago, people would take a bulldozer into a creek to shore up the banks, diking it by pushing rocks and gravel up onto the stream bank. “Orphan” means no one owns, manages, or inspects this dike. More recently built dikes would be monitored and regulated.
In the past few years the provincial government has done engineering studies on streams with orphan dikes around the province. Dikes on Duhamel and Crawford Creeks were deemed very likely to fail. Crawford Creek had the highest risk rating possible.
So Johnson and his staff knew they were looking at possible dike failures during this storm, with potentially disastrous results.
“The creek levels on Duhamel and Crawford Creek were climbing up incredibly steeply. And if we hit a certain point we decided we’ve got to get [the residents] out of there. Because if this goes, we have like tens of minutes to get people out.”
He knew they would need a couple of hours to go around and knock on doors and notify people. So, balancing the risk and consulting with engineers and hydrologists, they issued an evacuation order for specific properties.
Based on historical data, Johnson says, this storm was a 100-year event. That means a storm of similar severity is likely to happen once per century, or that there is a one per cent chance of it happening in any given year.
In Crawford and Duhamel Creeks about 300 people were given evacuation orders, with instructions to check in at the Kokanee Springs Golf Course and the Best Western in Nelson respectively. Johnson doesn’t know how many people actually left their homes because many went to stay with friends. But 40 per cent of the people given notices in Duhamel checked in to the Best Western.
It’s not necessarily just a question of leaving the house and coming back a day later to life as usual.
Johnson said throughout the region his office had to do several tactical evacuations in which they rescued people trapped behind log jams or in other hazardous situations.
He said as of Monday afternoon there were people whose houses are completely cut off, and many who will have to repair roads or structures.
“People are still in danger now, potentially. There are over 400 streams, little watersheds, throughout our region. And so after what’s gone on, there could be a gust of wind and a bunch of trees that are eroded along the bank fall in a creek, causing a log jam and it starts damming.”
He said people on local water systems should be careful when checking their water boxes.
A similar situation applies to Broadwater Road in Robson, where high waters closed the road and caused an evacuation order that has since been rescinded.
Evacuation orders in Ymir and Salmo were not based on individual creeks, as in Duhamel and Crawford, but on many streams that affected the Salmo River in a way not normally seen.
“The River Forecast Centre isn’t aware of the last time we had this type of hot weather with a high snowback and then torrential downpours,” Johnson says. “That was the equation that hit Grand Forks in 2018 [when disastrous flooding occurred there].”
Johnson said the evacuation addresses were determined by recent engineering studies and computer modelling of a range of weather and topography factors in the drainage.
More than 250 households in Ymir and Salmo were given evacuation orders, but Johnson doesn’t know the numbers of people who actually left, again because some people went to stay with friends and also because the order was lifted after less than 24 hours.
An evacuation order was also issued for homes along the Slocan River late Saturday, but rescinded within a few hours. Springer Creek overflowed its banks, inundating the Village of Slocan’s campground.
Prior to issuing the orders, the RDCK took the unusual step of issuing an evacuation alert for all properties next to rivers, creeks, and streams, except those in Nelson and Castlegar.
The Crawford Bay transfer station has been closed indefinitely, as parts of Crawford Creek Road washed out.
Calculating the risk
Johnson said decisions to order evacuations are made with the best information available during a compressed time frame.
“I can assure you it is no small task to evacuate people and find a place where they’re warm, safe, dry and fed. These are monumental undertakings that, if we didn’t have to do, we would not do.”
The decision to lift an evacuation order can be as difficult as the one to impose it. How do you decide it’s safe for people to be at home?
“When people are out of their homes — with the stress and the anxiety — the longer you extend that period, the more difficult recovery is, the greater the trauma is. So we’re always trying to get people back into their homes.
“When we saw that risk come down, we removed the order when we were OK with that level of risk. We do that with the experts [engineers and hydrologists] working with the best information we have at the time.”