MACKINAW CITY, MI -- What happened to the west leg of Line 5?

Of the 22 anchor supports that Enbridge Inc. is seeking permission to install on the twin 20-inch pipelines crossing underneath the straits of Mackinac, 17 of them are on the west leg.

Of those, five of the proposed anchors are clustered along several hundred feet of the west leg just north of where inspection reports show the pipeline is bent and "ovalized," a term for a section of pipe that's been misshapen enough to lose its roundness.

Documents show that section of pipe is bent in five places and ovalized twice. It's not known for sure how the deformities happened, but Enbridge says they are nothing to worry about, pointing to recent pressure testing as evidence the pipeline is in good shape.

However, inspection reports show that both ovalizations have worsened slightly since 2013.

The anomalies are documented in 2013 and 2016 inspection reports generated by sending "geoppig" robots inside the pipeline to check for problems. The anomalies are also referenced in the 2017 draft analysis of Line 5 released by Dynamic Risk Assessments, which speculates the bends occurred during 1953 construction.

But a retired fluid dynamics expert who has exhaustively studied Line 5 suspects that underwater currents long ago scoured a large section of lake bottom from underneath the pipe, leaving it free-spanning with nothing underneath to support its weight.

His theory is that, buffeted by tremendous currents in the straits, the long unsupported span eventually gave into the force of gravity, sagged and touched the bottom.

"It's the only area in the whole damn thing that's that way," said Ed Timm, a former Dow Chemical engineer who authored an independent technical report on metal fatigue in Line 5 this year that was released by the National Wildlife Federation.

"They want to put five supports in an area of the pipe that was damaged somehow, somewhen."

The five bends and two ovalities are about 70 feet underwater, located roughly one mile north of the Lower Peninsula shoreline. Two of the bends are located within three feet of a "girth weld" along the pipeline circumference; welds which joins Line 5 sections together.

The bends range in direction and severity, from 1.6 to 7.7 degrees.

The pipeline is ovalized by 5.7 percent in one place and 9.2 percent in the other. Both ovalities have increased slightly recent years. In 2013, the pipe sections were ovalized by 5.45 percent and 8.8 percent. The threshold for reporting an ovality is if it makes the pipe out of normal roundness by more than five percent.

They are located near a 52-foot unsupported span referenced in documents as "W-11." In a listing of spans between 2005 and 2016 disclosed to the state this year, Enbridge notes that anchors should be installed "to support deflection area just south of span W-11."

After discovering currents had created several long unsupported spans during the 2016 inspection, Enbridge installed four anchors to bring Line 5 back into compliance with the state easement, which does not allow unsupported spans greater than 75 feet.

The company wanted to install another 18 anchors as "proactive" maintenance, including five around the W-11 span, but the state only permitted those required to bring the pipeline into compliance after consulting with Native American tribes.

Michigan tribes, which are collectively opposed to the operation of Line 5, say any additional anchors required beyond what's needed for easement compliance should legally be considered new construction and would thus require an environmental impact assessment.

Enbridge says anchors are needed by the W-11 span because "there is a slight elevation change of the lake bed there and we wanted to add additional pipe anchoring/support," said spokesman Ryan Duffy, who responded to MLive inquiries via email and did not make Enbridge technical staff available to interview.

"There is a natural curve or bend in the pipeline, which was designed to follow the contour of the lake bed. The ovalization would be associated with the bend there," Duffy said. "All of our testing has shown there is no integrity issue in that section of pipeline, which is further supported by the conclusion in Dynamic Risk report."

The Michigan Department of Environmental Quality, which is jointly considering Enbridge's application for Line 5 anchors with the U.S. Army Corps of Engineers, is holding a public hearing on the application on July 25 in St. Igance.

MLive reached out to more than a dozen academic and public sector pipeline engineers and scientists around the world for an opinion about the severity of the bends and ovalization, and whether they fit the definition of damage. Only one responded, speaking on the condition of anonymity because he often works with Enbridge.

Ovalization, he said, is generally considered more of a "serviceability" than a safety concern because it can impede movement of in-line inspection tools. Ovalization can be fixed through hydrostatic pressure testing of the type that Enbridge conducted this year by putting water through the lines at 1,200 and 700 pounds-per-square-inch (psi). The extra pressure inside the pipe can re-inflate, so to speak, the misshapen area.

What's important, he said, is to understand what caused the ovalization. It can occur during initial pipe laying across the bottom, but can also happen because of underwater current stress on an unsupported span.

"Excessive ovalization can lead to buckling or wrinkling of the pipe," he said, which can be an integrity concern. "If bending is what is causing the ovalization, then the supports would mitigate any additional bending and would prevent future buckling from occurring."

James Mihell, an engineer who led development of the Dynamic Risk report, declined to speak about the report's characterization of the bends and ovalization, saying all communication about the report is supposed to be conducted through the state Pipeline Safety Advisory Board website, which is soliciting feedback on the draft analysis.

Page 103 of the report state that "while significant ovalities can, under certain circumstances impair the passage of in-line inspection tools, the strain associated with these features is normally broadly distributed around the pipe circumference, and thus, ovality is not generally considered to be a feature that poses an integrity threat."

According to the Dynamic Risk report, an anchor strike from a ship is the biggest threat to the pipeline, followed by a failure and corresponding spill caused by an unsupported span that is heavily beaten by underwater currents. The strength of flow in the straits between Lake Michigan and Lake Huron can be 10 to 20 times the 6 million daily cubic feet of water over Niagara Falls, according to noted water current scientist David Schwab.

The Dynamic Risk report has its critics, including state pipeline board members Mike Shriberg, Jennifer McKay, Craig Hupp, Guy Meadows and Chris Shepler, who say the report relies on flawed methods to systematically underestimate the probability, size and impact of a spill, and takes an approach "that assumes that the citizens of Michigan are responsible for ensuring that Enbridge Energy can deliver its products."

Timm argues the report basically ignores extreme current velocities from a serious storm in its risk modeling and does not consider what kind of stress the pipeline endured prior to 2003, the earliest year of inspection reports analyzed by the state-contracted report.

Enbridge documents that surfaced this year show the company only got serious about fixing erosion under Line 5 in 2001 after allowing many unsupported spans greater than 75-feet to go unchecked for years. Reports filed with the federal government reference a 2003 survey that identified 16 unsupported spans greater than 140 feet; the longest at 224 feet on the east leg and 286 feet on the west leg.

An Enbridge engineer wrote in a 2001 application to install supports that, "in order to maintain pipeline integrity and safety, these maintenance repairs can wait no longer."

Timm said it makes perfect sense that Enbridge would want to put several anchors on the section of pipeline where the bends and ovalization is found. He said the ovalization is a significant indication that "something happened."

"I think Enbridge knows darn well that pipeline had better have all the support under it as possible," he said.

The St. Ignace public hearing will take place July 25 at Little Bear East Arena in St. Ignace from 1 to 4 p.m., immediately prior to a meeting to hear public comment on the Dynamic Risk report.

Written comments may be submitted at the public hearing, directly to the DEQ through the MiWaters database (click here), or mailed to the DEQ Gaylord Field Office at 2100 West M-32, Gaylord, Michigan 49735.