Ice scour

A Beaufort Sea oil project involved oil production on artificial islands. The oil would be sent through pipes to the shore in a sea area known for very deep ice scours in the ocean bed. These deep scours would threaten a pipeline even if it were buried 3 or 4 m beneath the sea bed, many times deeper than conventional pipe burying. The key criterion, level-one, primary source of uncertainty Chapman was asked to address (by the project manager) was 'ice scour damage' to the pipeline. He addressed this question in terms of a second level of uncertainty involving two components to the question 'what was the chance of ice scour damage?':

• What was the chance ice would strike the pipeline?

• What was the chance that an ice strike would seriously damage the pipeline?

Chapman was also asked to take the second of these questions to deeper levels by the company ice scour experts, addressing the questions:

• What was the uncertainty in their data, with a view to assessing what type of additional data would be most useful (e.g., more seasons or a wider area within a season)?

• What was the uncertainty in the statistical model used to estimate the likelihood of scours at different depths?

Further deeper levels could be associated with the alternative mechanisms associated with generating scour (ice heave during freezing versus grounded ice during thaws), and so on.

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