2018-07-07 / Top News

Gravel Could Protect Line 5, Enbridge Says

State Receives New Reports on Pipeline
By Stephanie Fortino


This diagram illustrates a cross section of the gravel barrier that could be installed on Line 5 to protect the pipelines from vessel anchor strikes. The diagram is taken from Enbridge’s recently published report. This diagram illustrates a cross section of the gravel barrier that could be installed on Line 5 to protect the pipelines from vessel anchor strikes. The diagram is taken from Enbridge’s recently published report. Enbridge published another set of reports about Line 5 Friday, June 30, which include a plan to cover the existing pipes at the Straits of Mackinac with gravel to minimize the risk of another anchor strike. The company also suggests more warnings, including signage and a communication system, to remind mariners not to anchor when running through the shipping channel.

Another report details the 400 lakes and streams that Line 5 crosses in Michigan. The final report explains the current state of Line 5’s coating system and finds that other leak-detection technology is not feasible where the pipelines cross the Great Lakes.

The reports are the result of the November 2017 agreement with the State of Michigan. Governor Rick Snyder has said a final decision about the future of Line 5 will be made this fall.


If Line 5 were to be covered with a gravel and rock barrier, the material would be piled higher where anchor screws support Line 5 across washouts on the lake bottom, as shown in this diagram taken from a recent Enbridge report. If Line 5 were to be covered with a gravel and rock barrier, the material would be piled higher where anchor screws support Line 5 across washouts on the lake bottom, as shown in this diagram taken from a recent Enbridge report. The four reports can be viewed at the Town Crier Web site in the General Documents tab.

Anchor Strike Report

The anchor strike report, more than 100 pages long, reviews warning systems already in place at the Straits of Mackinac and outlines plans for new communication technology and the gravel barriers. The company hired an engineering consultant who assessed options for protecting Line 5 underwater and concluded the use of gravel would be most effective.


This map of Line 5, taken from Enbridge’s recent anchor strike report, shows the Upper Peninsula on the left and lower peninsula to the right. The rectangles indicate the portions of the twin pipelines over which most of the Straits of Mackinac shipping traffic occurs. The area could be covered with gravel to protect it from a dropped or dragged anchor, according to Enbridge. This map of Line 5, taken from Enbridge’s recent anchor strike report, shows the Upper Peninsula on the left and lower peninsula to the right. The rectangles indicate the portions of the twin pipelines over which most of the Straits of Mackinac shipping traffic occurs. The area could be covered with gravel to protect it from a dropped or dragged anchor, according to Enbridge. Findings by the consultant then were reviewed by constructability, environmental, and reliability consultants to determine if the barrier could be built, how it would impact the environment, and whether it would adequately reduce the risk from an anchor strike.

In all, 15 ways of adding protective barriers to Line 5 were reviewed, —tension cables, concrete barriers, and steel covers among them. The barriers were analyzed according to how well they protected the pipelines, whether they posed a risk to the pipes during construction, and whether they would interfere with shipping and recreation during construction, according to the report.


A gravel barrier installed on Line 5 would be thick enough to protect the pipelines if an anchor was dropped to the side, according to this diagram from Enbridge. A gravel barrier installed on Line 5 would be thick enough to protect the pipelines if an anchor was dropped to the side, according to this diagram from Enbridge. Gravel and rock protective barriers are utilized in the global offshore pipeline industry, Enbridge says, and are effective at protecting underwater pipes in some of the busiest harbors and shipping channels. Under the proposal, all 11,000 feet of the east pipe and 12,000 feet of the west pipe would be covered in rock and gravel, costing an estimated $150 million. The project would take two to three years.

The barriers would be comprised of a rock and gravel barrier covered in a layer of larger rocks. Where the Line 5 pipes rest on the lakebed, gravel and rock would be piled eight feet high and more than six feet above the pipe. Where the lakebed has washed away and the pipe rests on anchor screw supports, the gravel would fill the washouts and be piled 11 feet high. The gravel barriers would be about 72 feet wide, extending across each 20-inch pipe.


This map, taken from Enbridge’s recent anchor strike report, illustrates the density of ships traveling through the Straits of Mackinac. To reduce the risk of another anchor strike, the company proposes covering the pipelines with a gravel barrier, which could extend the whole length of the pipes, or just where most boats travel. Line 5 is about two miles west of the Mackinac Bridge. This map, taken from Enbridge’s recent anchor strike report, illustrates the density of ships traveling through the Straits of Mackinac. To reduce the risk of another anchor strike, the company proposes covering the pipelines with a gravel barrier, which could extend the whole length of the pipes, or just where most boats travel. Line 5 is about two miles west of the Mackinac Bridge. Another option, Enbridge says, would be to cover only the portions of Line 5 that cross the shipping channel, which is about 700 feet wide for the east pipe and 800 feet wide for the west pipe. A buffer on each side of the shipping channel should be added, Enbridge’s engineering consultant advised, so a total of 2,000 feet of both pipes would be covered.


If a gravel barrier is installed along Line 5, this diagram shows what would happen if an anchor were to be dropped on the pipeline from directly above. The twin pipelines would be protected, says Enbridge, which recently published a report on how to reduce the risk of anchor strikes. If a gravel barrier is installed along Line 5, this diagram shows what would happen if an anchor were to be dropped on the pipeline from directly above. The twin pipelines would be protected, says Enbridge, which recently published a report on how to reduce the risk of anchor strikes. If the entire length of the pipelines were to be covered, about 360,000 cubic yards of gravel and rock would be required. If only the shipping channel portions and a buffer were covered, about 85,000 cubic yards of gravel and rock would be needed.

The engineered gravel barriers would mitigate the effects of the largest vessels dropping or dragging their 10.2-metric-ton anchors on or across Line 5, Enbridge says. The reliability consultant found that the barrier would reduce the risk of a pipeline failure because of an anchor strike by 99%.

Since the gravel barrier would prevent Enbridge from visually inspecting Line 5, the company would continue use in-line inspection tools to evaluate the integrity of the pipelines, the report says. The company regularly would inspect visually the gravel barrier to make sure there is adequate coverage. Should exterior visual inspections of the pipes be needed, underwater equipment and divers could remove the gravel, Enbridge says.

The report recommends a coordinated “public awareness campaign” about the utility crossings in the Straits of Mackinac, as well as signage on the Mackinac Bridge to warn vessels. In the shipping channel, floating buoy markers with “no anchor” warnings could be added. Dedicated vessels or drones could patrol the Straits. Vessels could be subject to mandatory anchor inspections at new checkpoints before sailing through the shipping channel, Enbridge suggested.

Technology to notify vessels as they approach Line 5 is another recommendation. Enbridge evaluated options for that and decided the Internet based “Guardian:protect” system from Vesper Marine could work at the Straits. If that system were pursued, a pipeline user could identify, track, and communicate with vessels near its underwater assets, such as Line 5. It would allow users to send warnings automatically as the system detected shipping activity that could threaten Line 5. Warnings would be sent to the vessel and user.

Such a system has been installed at Enbridge’s pumping station in Mackinaw City. If the system were to be implemented on a larger scale, the U.S. Coast Guard and Federal Communications Commission, along with other agencies, would help decide whether the system should communicate with vessels and what the messages would say. The messages could include reminders for mariners to check that their anchors are up and properly stowed, as well as warning messages to ships that appeared to be anchoring. Implementing the full system would cost about $500,000.

Water Crossings Report

A state technical team that worked with Enbridge to develop the report found that Line 5 crosses 400 bodies of water in Michigan. Prioritizing the crossings, the team developed a list of 74 water crossings of highest importance. Those crossings were grouped by region, resulting in 11 areas for each of which Enbridge reviewed leak mitigation programs, potential risks, emergency response, and environmental management. The company developed plans to reduce leaks.

The 11 areas include:

• Lake Gogebic (two priority water crossings)

• Watersmeet, Iron River to Crystal Falls (one priority water crossing)

• Rapid River to Manistique (10 priority water crossings)

• Rock River to the Straits of Mackinac (17 priority water crossings)

• Mackinaw City to Indian River (seven priority water crossings)

• Au Sable Watershed (three priority water crossings)

• Saginaw Bay (19 priority water crossings)

• Vassar (two priority water crossings)

• North Branch Mill Creek (one priority water crossing)

• St. Clair (six priority water crossings)

Enbridge suggests that each area have increased safety targets installed, have established emergency response training and communications, updated environmental sensitivity maps, and Michigan Association of County Drain Commissioners public outreach. Dent reliability assessments will be performed on the Rock River to Straits of Mackinac, Mackinaw City to Indian River, Iron River to Crystal Falls, and the Rapid River to Manistique areas. A detailed engineering assessment will be performed on the Rock River to Straits of Mackinac area portion.

Enbridge also outlined how long it will take to conduct each aspect of the reports at the water crossings and grouping areas. Increasing safety targets will take six months and the dent reliability assessments will take 12 months. The engineering assessment, geohazard assessment, bathymetric survey, and a scour study will take 18 months.

It will take six months to review the emergency response training and exercise communication plan and public outreach through the Michigan Association of County Drain Commissioners. Updating the environmental sensitivity maps will take 12 months, as will the review of the emergency response aquatic invasive species inspection procedure.

The State Technical Team will work with Enbridge to complete environmental studies, including an analysis of rare wetlands, and a biological mitigation study, which will focus on fisheries, freshwater mussels, and biological integrity. These studies will take 18 months.

The water crossings report is 38 pages long.

Pipeline Coating and Leak Detection Reports

Enbridge also reported on nine methods for detecting damage to protective coating. Cathodic protection close interval surveys, direct current voltage gradient surveys, alternating current voltage gradient surveys, alternating current attenuation surveys, alectromagnetic acoustic transducer in-line inspections, cathodic protection current mapper in-line inspections, metal loss in-line inspections, visual examinations, and high-voltage holiday detections.

Seven of the technologies use electrical, electromagnetic, and/or ultrasonic measurements to identify gaps in coating. While they are used in the pipeline industry, Enbridge says, most of the technologies haven’t been widely used on underwater pipelines.

The cathodic protection close interval survey is the best method to find coating damage, according to the report. The survey, when used with a metal-loss in-line inspection tool, is the most-reliable way to evaluate and manage external corrosion where Line 5 crosses the Straits of Mackinac, says Enbridge. Such a survey and inspection will be completed in 2018.

As required by the November 2017 agreement with the state, the 26-page-long leak detection report evaluated three underwater methods to find pipeline leaks. The technologies included fixed optical cameras, fluorescent leak detection, and distributed acoustic sensing cables.

The report finds that none of these methods can be used continuously to detect pipeline leaks underwater. None of the technologies are feasible at the Straits of Mackinac. Enbridge has installed the a hybrid leak detection system as another layers of leak detection of the Straits of Mackinac.

Return to top

Thank you Stephanie Fortino

Thank you Stephanie Fortino and Town Crier for this outstanding report, delivered with the dispatch and accuracy this vital news merits. Reading between the lines, and taken with the voluminous findings about the ticking time bomb we call Line 5 -you've documented for history, the negligent disdain Enbridge continues to demonstrate about safety, the Great Lakes and the economy of Northern Michigan dependent on a healthy, secure Straits of Mackinac.
Click here for digital edition
2018-07-07 digital edition