Aerial image shows the 230-kilovolt line tower that collapsed Monday (left) and the 500-kilovolt line tower (right) that Hydro crews braced and de-energized last week out of stability concerns.

Tower collapse a surprise despite work to brace its twin

Timeline lays out sequence of events leading to emergency

BC Hydro CEO Dave Cobb says there was no advance warning a transmission tower was about to topple into the Fraser River even though engineers had already bolstered an adjacent tower that was leaning due to high-water erosion.

The tower supporting the 230-kilovolt line across the river fell Monday night after Hydro crews declared it stable.

Cobb said the adjacent 500-kilovolt line – which crosses the river immediately upstream – was the focus of concern because river water was undercutting the footings of its tower on the Surrey side.

Hydro put supporting cables on the 500-kv tower a week earlier and de-energized the 500-kv line four days before the neighouring 230-kv tower collapsed just metres away.

“There was no indication that the 230-kv line was at heightened risk,” Cobb said in a statement.

“We will bring in external hydrology experts and engineers to help us determine with certainty the cause. We will rigorously double-check similar transmission structures that may be affected by high water levels to ensure the long-term stability of the transmission towers.”

Coquitlam Mayor Richard Stewart said the fact Hydro knew for several days that there was potential for trouble with the towers in the area means municipalities should have been alerted so they could step up emergency preparations.

Cobb said Hydro will review its emergency notification protocols to address local cities’ concerns.

A review of the incident and repairs to the transmission line are to be complete within a month.

 

TIMELINE

June 11: BC Hydro discovers the tower supporting the 500-kilovolt (kV) transmission line (upstream line) on the south side of the Fraser River had been damaged, presumably by a barge. BC Hydro secures the tower, begins engineering assessments of the foundation and plans for repairs.

June 16-30: BC Hydro surveys tower foundation every two days to assess footings and begins weekly subsurface in-river stability checks.

June 27: Temporary support (guy) lines installed on the 500 kV line. Situation is deemed stable by BC Hydro engineers.

Thursday, June 30: The area around the 500-kV tower begins showing signs of erosion. The road adjacent to the tower sloughs into the river causing the tower to drop four feet and shifts the tower top over 20 feet. The 500-kV line is de-energized as a precaution. A safety observer and surveyors are put on site 24/7 to monitor the situation. BC Hydro starts design work for more supporting guy cables.

June 30: CN Rail starts installing rip-rap (loose stone used to form a foundation for a breakwater or other structure) to rebuild the road; BC Hydro footings simultaneously get rip-rap.

July 2 – 4: BC Hydro conducts daily aerial surveys and underwater survey of neighbouring tower supporting adjacent 230-kV transmission line that crosses the river just downstream of the 500-kV line – and this tower’s foundation is deemed stable.

Monday, July 4: As the Fraser River crests, there appears to have been sudden and unexpected erosion on the south side of the river, causing the 230-kV tower to fall into the Fraser River just before 9 p.m. The fall of the tower brings down additional transmission poles and infrastructure, causing tension and strain on attached lines.•  There were no injuries and no safety risk posed by the wires as protection equipment was activated when the lines toppled and they were de-energized automatically. •  About 25,000 customers in Surrey suffered a power outage. BC Hydro crews were able to respond quickly and conduct switching to restore power to most customers within 45 minutes. Power was restored to all but a couple hundred customers just after 11 p.m. • Authorities shut down Highway 1, the Lougheed Highway, the Port Mann Bridge and portions of United Boulevard in Coquitlam to ensure public safety. Marine traffic was also affected and managed by the Canadian Coast Guard. • BC Hydro officials worked throughout the night to ensure the stability of other towers and crews worked in conjunction with emergency officials to clear the fallen infrastructure.

Tuesday, July 5, 7 a.m.: Highway 1 and Lougheed Highway re-opened to traffic. Crews successfully remove remaining cables that fell on the roads by 10 a.m.