The Yukon Energy Corporation will come in with the most expensive repair bill from flood damage in 2021.
The damage that occurred as a result of the boat lock on the Yukon River at Marsh Lake being open all summer is still being assessed and it could take years to repair.
Andrew Hall, president and CEO of Yukon Energy Corporation (YEC), was frank. He said they asked more of the locks on the control structure last season than it was designed to do.
“The boat lock wasn’t specifically designed to do long-term conveyance of large flows of water. Look what happened,” Hall said.
YEC opened the control gates in mid-March, but when flooding surged in June 2021,they opened the lock, and then removed the gates completely in a full-scale effort to keep the high waters moving through the system of rivers and lakes unimpeded.
But in the fall, as the water levels dropped, the consequences of all that extra water showed themselves. The downstream bank had eroded and water flow was undercutting the fill of the island which forms the base of the control gate structure.
“The island forms part of the structural integrity of the lock,” Hall said.
“We were particularly concerned about that island. We are starting to see some erosion of the inside of the island, which suggests that the waters are kind of getting up underneath that, what is called ‘sheet pile,’ the metal cladding, and starting to erode it from the inside out.”
Last July, YEC loaded huge sandbags onto the top of the island. The bags protected the island if water levels rose over, Hall explained.
Now, YEC needs to inspect exactly what is happening underneath the island from the deep circular flow of water. That, he says, will require permits from the Yukon Socio-economic Assessment Board, the Water Board and perhaps the federal Department of Fisheries and Oceans because they will have to build temporary dams to conduct the inspections.
On a Zoom call with Southern Lakes residents on Feb. 23, Hall showed photos of the emergency repair work that has been done so far. The eroded bank has been filled with rip-rap and rocks, and a gravel berm has been constructed across the lock to stop the flow of water through the locks.
“That wasn’t completely water-impermeable, so we still had a bit of flow going through and then we put a sluice gate to physically block off the whole boat lock,” Hall said.
The emergency fix has been completed, though it means the loss of the boat lock system for the upcoming summer and one less channel for water to flow through. In the fall, YEC will isolate the damaged area, pump out the water to see the real extent of damage to the underpinnings of the island, and assess the best options for a rebuild.
There are people who have been concerned that the control gates act as a chokepoint for the water coming into the Yukon River from the south. Hall admits that last year’s flood could have been worse if not for the weather, but prediction “is a really complicated process.”
The new design will likely include a means of spilling more water through or around the new boat lock. Boat locks are a requirement of the Canadian Navigable Waters Act.
“You really can never tell ahead of time how high the water levels are going to get,” Hall said.
Now recent experience and necessity are providing the opportunity to rebuild better and smarter, preparing for the possibility of more extreme weather and climate threats in the long term. This summer’s flood predictions are a short while away.
Correction: An earlier version of this story stated the control gates were opened in June, when they were actually opened earlier than usual, in mid-March. The island is made of “sheet pile”, not “cheap pile” as was written in the earlier version.
Contact Lawrie Crawford at firstname.lastname@example.org