Heavy rains overwhelmed temporary drainage measures and flooded the new underpass at the McKenzie interchange on the Trans-Canada Highway Tuesday morning, backing up traffic for hours.
At about 4 a.m. a contractor at the construction site for the $96-million Trans-Canada and Admirals Road/McKenzie Avenue interchange realized a mix of ditches and pumps was being overwhelmed by heavy rainfall. “Obviously they were aware the rain was coming,” Janelle Staite, deputy regional director for the Ministry of Transportation, said of the forecasted storm.
“Unfortunately, the system got overwhelmed which wasn’t anticipated and they reacted swiftly to make sure that we could re-open the highway and make sure that there wasn’t standing water or pooling water in the slow lane.”
The final drainage system will include a manhole-type drainage infrastructure and large pipes with a one-in-200-year-storm rating.
“The permanent drainage system will safely and adequately handle a one-in-200-year flow without disruption to traffic or compromising the safety of those using the interchange,” said the ministry in a statement. “The permanent system is meant to handle significant storm events; there is ample capacity in there,” said Staite. “This event today has no bearing on the final configuration.”
Once the interchange is finished, water from the highway will head into a storm-water retention pond in the middle of the loop ramp “so it will have much more capacity to be able to handle water like we saw yesterday and handle even more severe storm events where there’s significant amounts of rain.”
Given Tuesday’s flooding, pumper trucks will be on standby on the construction site in case of another significant rain or water event, said Staite.
The ministry said Highway 1 southbound was open to traffic at 7:45 a.m. One northbound lane remained closed, however, “for an additional couple of hours to assist with the staging of the additional pump trucks.”
Staite described the underpass as bowl-like with rain flowing into it from each direction. Holes in roadside barriers allowed water to drain into ditches.
“Ultimately the ditches on the backside of the barrier just got overloaded with water,” said Staite. “Even though we were pumping that water out of the ditch and into a temporary piping system that ultimately went off site, the water that was going into that temporary piping system, it was too much for it to handle.
“There was nowhere for the water to go so that’s why we actually brought in pumper trucks into the southbound lanes,” said Staite.
Companies were called by the contractor to bring in four extra pumper trucks to deal with the overflow.
At 5 a.m., Saanich police said they responded to a report of flooding on the road and helped with traffic control until flaggers arrived.
Trans Canada Highway traffic was reduced to one lane in each direction, said Saanich Const. Markus Anastasiades. The flooding was in the slow southbound lane and equipment was placed in the slow northbound lane.
Police left the scene at 6 a.m.
Morning commuter traffic was backed up for hours.
“Heavy rains over the last 48 hours overwhelmed the temporary drainage measures the contractor had in place,” said the ministry.
“If the contractor anticipated that those temporary measures wouldn’t have been adequate they would have had measures in place,” said Staite. “So now that it’s come to our attention that what was in place wasn’t adequate we’ll make sure those measures are in place.”
Work began on the interchange in September 2016. The price tag at the time was $85 million, but an $11-million cost overrun was announced in June due to design changes, weather delays and other problems.
The underpass opened on Dec. 19, allowing Highway 1 traffic to flow freely where there was once a traffic signal.
The full interchange project was scheduled to be completed in 2018 and is now expected to be completed by the end of this summer.
