A bird’s eye view of the terrain above Trail has revealed a major “hot spot” that could threaten homes with flooding in West Trail along Gorge Creek.
There are three sluff areas poised above the city—loaded with logs, branches, leaves, rocks and soil—that could cause more landslides and flooding if they are not taken care of, Coun. Gord DeRosa told Trail city council Monday night at a regular meeting.
On Monday afternoon the hot spot was discovered after the city sent its public works manager and a geotechnical engineer up in a helicopter with members of the Provincial Emergency Program (PEP) from Nelson to assess any potential trouble spots brewing after Trail was waterlogged with flotsam and jetsam spewing down from its bounding upper rocky reaches Saturday.
Those areas are amassing debris, said DeRosa, around the breaks of a flue where it enters the channel of the creek. If the debris builds up and water breaches the area the city is “in trouble,” as it was when Trail Creek flooded the Gulch in 1997.
There is “a very serious one higher up that needs to be resolved,” DeRosa said. “These all come as a surprise, of course, and things can happen very quickly.”
With over 180 millimetres of rain this month feeding the rising waters of Gorge Creek, the creek’s banks are eroding. Once the bank sluffs into the creek, if it doesn’t actually block the creek and produce a pool behind it, in releasing it will carry with it debris that will plug off the flue, leading to a mudslide.
“We’re in about as good a shape as anyone, but you never know,” said Mayor Dieter Bogs, about the likelihood of a slide.
However, city engineering and public works management will be looking at ways and means of dealing with the hot spots before they become a problem, DeRosa noted.
Upon receiving notification for the work, PEP—a provincially-funded organization that provides support before, during and after emergencies—will pay up to 80 per cent for the total cost of the work, with the city on the hook for the remainder.
The city will have to remediate the entire area, including installing riprap—rock used to armour shorelines and shorelines structures against scouring or water erosion—and cleaning up the existing debris.
“But you can’t protect the whole gorge, there is just no way,” said Bogs.
PEP had hired the helicopter to survey all of the higher reaches of the city to ensure there was no further sluffing in the creek beds around the city that would result in debris coming down and collecting in the city’s intakes.
There wasn’t. One trouble spot expected above Sunningdale did not materialize, said city public works manager Larry Abenante. A new creek bed sent debris down off of the rock face, but there was no pooling of water on the mountain’s top, he said.
“I think we just had so much rain that things just picked up,” he said.
The rain event on Saturday outstripped the ability of the city’s 80-year-old storm system to carry the rainwater away, said DeRosa. Sewer lift stations had trouble as well dealing with the water volume, especially since their outfalls into the Columbia River were underwater.
The load resulted in a backed up system that released some sewage onto Fifth Avenue.
“Now we have to look at our systems and ask ‘Why did this happen? How could we correct it?” said DeRosa.
The storm sewer system in the city was designed over 80 years ago. When the opportunity arises the city will oversize the pipes, DeRosa explained, especially now knowing full well they will be dealing with heavier rainstorms.
“They are not a 200-year event anymore, they are going to be a norm,” he said. “We have to look very, very carefully at our infrastructure and when we can we have to prepare for the extreme.”
A $350,000 fix a couple of years ago in the Third Avenue area of East Trail failed to correct an underperforming storm system, however. With the outfall underwater the system backed up and flooded the neighbourhood.
DeRosa said the rain on Saturday swelled the banks of the Columbia River and eroded the soil underneath the Trail Bridge. Earth was sluffing into the river where it has exposed some “real heavy riprap,” he said.
The observation will be reported to the Ministry of Transportation.
Across the region evacuation orders remain in place for Slocan Valley West Road while others—in the Pass Creek, Goose Creek area, and one residence on McLean Road north of Robson —were rescinded. Water is still flowing over the valley road and it was expected to be closed until Thursday.
The Slocan River near Crescent Valley is currently at 500 cubic metres per second (the height of its five-year flow). Additional rises are expected over the next two days as more rain comes in, meaning it could climb back to 650 m3/s.