Why is Gladstone's Old Trolley Bridge collapsing?

Why is Gladstone's Old Trolley Bridge collapsing? »Play Video

GLADSTONE, Ore. - Sun breaks Friday brought people out of their homes to Gladstone to visit the Old Trolley Bridge over the Clackamas River.

Some took pictures; some just took a moment.

Among them was Tammy Stempel, who had to fight back tears.

"Seeing it's worse off than it was yesterday, my heart is broken," she said. "Not for me but for the community."
 
Stempel's been working working for months to secure a grant and turn the bridge into something people on foot and on bikes can use. The grant came through recently, and a feasability study was scheduled for next week.
 
But after a sudden shifting of the bridge footing on one side early Thursday morning, leaving the span tilted and sinking, Stempel has been praying.
 
"My knees are worn out from being down and praying there can be a miracle that can save the bridge," she said.
 
The bridge is owned by Union Pacific. Company spokesman Aaron Hunt told the On Your Side Investigators on Friday that engineers were on site around the clock trying to assess damage and develop a mitigation plan.
 
Hunt said to expect heavy equipment brought in over the weekend to help engineers with their analysis, including a truck to lower them down and a dock on the water. 
 
Stempel's husband is Gladstone Fire spokesman Lt. Kirk Stempel.
 
Asked why officials don't just begin dismantling it before it falls into the river, he said the water current in the Clackamas River under the bridge is a challenge, pointing out how sheriff's deputies were struggling to keep their boat stationary as they checked the bridge out Thursday.
 
"They're looking at shoring it up somehow, waiting until the water level comes down," he said. "But it's best if Mother Nature is just going to complete the task (of collapsing it)."
 
Clackamas County engineer Mike Bezner, who has surveyed the bridge since the footing shifted, said the bridge has scour underneath, areas where sediment has been scooped out by swiftly moving water. He said scour is one of the main causes of bridge failure. 
 
With a historic structure built in 1893 that has withstood more than a century of extreme weather events, including the floods of 1996, many neighbors including Tammy Stempel are concerned this crisis is related to the water intake pump station being built nearby on the other side of the river.
 
Within the last week, a section of the coffer dam protecting the intake location's in-stream construction failed and began tilting out. It wasn't long before the bridge footing on the other side gave out as well, leading to the current predicament.
 
The pump station is a project by the Lake Oswego and Tigard Water partnership.
 
Stempel said since the station went int, the flow of the river changed and roughly 40 feet of beach across the river disappeared, covered by water. Other neighbors point to potential effects of the vibrations from the construction. 
 
You can read more about the pump station project here.