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Computer modeling shows the disastrous impact of a pipeline break

One oceanographer says it’s “the worst possible place” in the Great Lakes to have a major oil spill.

In this computer-generated image, oil from a hypothetical 12-hour pipeline leak on the north side of the Straits of Mackinac has moved into both Lake Michigan (left) and Lake Huron, with heavy loading of surface oil on the beaches of both Mackinac Island, closest to the break, and Bois Blanc Island.
University of Michigan Water Center/Graham Sustainability Institute

Shortly after Tuesday’s piece on the rising risk of oil-train accidents went up, I heard from a couple of readers who suggested that maybe I should also have addressed the issues around oil shipment via pipeline.

One, who took a mildly chiding tone, pointed out that the same environmental groups who oppose rail shipment of oil also oppose creation of new pipeline capacity — the only realistic alternative to more oil trains.

Another pointed out that both methods carry serious risks, which cannot be reduced without radical changes in American petroleum use, or in the infrastructure for distributing oil products, or both.

All fair points, and they reminded me of a piece of research I had laid aside last week for later consideration, on the subject of what a pipeline failure at the Straits of Mackinac could do to the Great Lakes basin.

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Now’s as good a time as any for a closer look at that work, and at the highly disturbing scenario it documents with what seems to me quite impressive scientific rigor.

Depending on your hydrological preferences, the Straits is either a 5-mile-wide waterway linking Lake Michigan and Lake Huron, or a narrows at the middle of a single Great Lake where the northern and southern shorelines come within five miles of meeting.

The watery gap is spanned by the Mackinac Bridge, connecting upper and lower Michigan. It is also spanned, under the surface and at depths of up to 270 feet, by Line 5 of Enbridge Energy Partners LP’s Lakehead System.

Line 5 originates in the port of Superior, Wisconsin, and runs to Sarnia, Ontario, at the southern tip of Lake Huron. At the Straits, it splits temporarily into two 20-inch-diameter pipes, laid in 1953, which can carry up to 23 million gallons of crude oil per day.

This is a key link in the Lakehead System, which originates in northwest North Dakota and which, like the rest of the North American oil-transport infrastructure, is growing ever busier with booming production in the Dakota and Alberta oil fields.

‘Worst possible place’ for spill

It is also, in the opinion of oceanographer David Schwab, “the worst possible place” in the Great Lakes to have a major oil spill.

Schwab recently retired from a 30-year career at the National Oceanic and Atmospheric Administration and its Great Lakes Environmental Research Laboratory; he now works as a research scientist at the University of Michigan Water Center.

Schwab’s longtime specialty is understanding the way lake water flows in the Great Lakes — from seasonal variations and seiches to storm surges — and developing models to predict these dynamics.

And he has had a special interest in the Straits, where the flow between Michigan and Huron has long been known to change direction every few days or so, and in understanding those patterns in three dimensions — not just surface flows, but movements of water up from the depths and back down again.

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Last December, he published a research paper in the respected Journal of Great Lakes Research that presented the first three-dimensional modeling of flows at the Straits. The methods laid out in the paper create a new capability “to investigate and accurately predict flow at the Straits of Mackinac and its effect on Lake Michigan and Huron” — which, the paper noted, in combination form “the largest lake in the world by surface area and the fourth largest by volume (containing nearly 8% of the world’s surface freshwater).”

Based on what he has learned about the way water moves between them, Schwab said in an interview with the Detroit Free Press last week, “I can’t think — in my experience — of another place on the Great Lakes where an oil spill would have as wide an area of impact, in as short of time, as at the Straits of Mackinac.”

The Free Press story concerned a more recent research project of Schwab’s, using three-dimensional modeling and computer animations to predict visually — so nonscientists like me, and most of you, might understand —how a major oil spill at the Straits would move into the two lakes.

And the answer is, catastrophically.

Six spill scenarios studied

The University of Michigan Water Center has posted animations of six scenarios prepared by Schwab, visualizing oil spills at three locations in the Straits (north side, south side, center) and two different times of year (drawing on actual flow data from Aug. 1-21, 1990, and from Sept. 23-Oct. 13, 1990).

In each scenario, spilled oil is shown with color-coded “tracer” dots at three depths: blue for near the lake bottom, red for near the surface, yellow for a middle depth. The tracers were assumed to have, like oil, no inherent tendency to float or sink. Each “spill” lasted 12 hours, and the tracers were tracked for 20 days.

The results, lightly compressed, of the simulations:


During this period, average currents in the Straits were initially eastward, but changed direction every day or two. Currents at middepth and bottom reverse direction sooner than at the surface and are moving tracers to the west after 2 days. Surface tracers from the southern release point have impinged on the southern shore of Lake Huron just east  of the Straits within 12 hours. Surface tracers from the central release impinge on Bois Blanc Island after 2 days.

Tracers from all depths at the northern release point are in the vicinity of Mackinac Island and Round Island after 12 hours, and near the northern shore of Bois Blanc Island after 2 days. Because of the initially strong eastward flow, surface tracers, and some of the tracers from middepth releases tend to be advected into Lake Huron and end up impacting the southern shoreline as far south as Rogers City after 10 days.

Tracers from nearbottom and middepth tracers from the southern and central release points are mainly offshore in Lake Michigan after 20 days. Curiously, most middepth and many near bottom tracers from the northern release point end up in Lake Huron offshore of Rogers City after 20 days.

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Average currents in the Straits were initially westward, but again changed direction periodically throughout the period. The westward flow carried all tracers into Lake Michigan during the first 24 hours. After 2 days, tracers from the northern and central release points were evenly distributed between the Lake Michigan side and the Lake Huron side while most of the tracers from the southern release point were in Lake Huron and impinging on the Michigan shoreline from Mackinaw City halfway to Cheboygan.

During this scenario, currents were more similar in direction from surface to bottom than in the August case. After 3 days, some surface particles from the northern release and particles from various depths from the central release were impinging on the southern shore of Bois Blanc Island. At 10 days, a large number of tracers were beginning to accumulate in an area halfway between the Straits and Beaver Island in Lake Michigan, and particles had been advected along the Michigan shoreline in Lake Huron past Cheboygan, but not as far as Rogers City.

After 16 days, some tracers from the northern release have reached Beaver Island in Lake Michigan. At 20 days, the majority of tracers from middepth and near bottom releases at all three locations, as well as surface release tracers from the northern location, are in northern Lake Michigan, spread between the Straits and Beaver Island. Most of the surface release tracers from the center location have impinged on the shore of Bois Blanc Island.

Enbridge’s other pipeline problem

The Schwab videos are being promoted by the National Wildlife Federation, which provided some funding for the project (a fact disclosed on the cover page of Schwab’s written report and in the videos themselves).

Enbridge’s response is that the Straits pipeline has never leaked, that the company’s inspection and maintenance programs meet or exceed all requirements, and that a full inspection last year involving new, remotely operated gear found no problems.

But it doesn’t dispute the modeling itself, according to the Free Press story, saying Schwab’s work will advance “continued and meaningful discussion on pipeline safety in the Straits.”

That’s a livelier discussion in Michigan these days than in many other places because of the July 2010 failure on Enbridge’s Line 6, near Marshall, Michigan, that released nearly 1 million gallons of diluted bitumen — tar-sands oil — into Talmadge Creek and then the Kalamazoo River.

That was the largest inland oil spill in U.S. history, and went unreported to local authorities for 18 hours. As the Kalamazoo makes a slow recovery, testing and skimming and scooping continue, and Michigan officials are pressing Enbridge for details of its contingency plans for a failure at the Straits of Mackinac.