New predictions of extreme keel depths and scour frequencies for the Beaufort Sea using ice thickness statistics

In 1983 Wadhams proposed a technique for calculating scour return periods and pipeline burial depths for scour avoidance for the coastal Beaufort Sea. The technique combined extreme keel depth predictions based on submarine data with the use of observed distributions of scour widths and incision depths, to calculate the extreme incision depth with a given return period for a pipeline of given length laid across the seabed. The Beaufort Sea submarine dataset used to illustrate the application of the technique was obtained in 1976 from a regime consisting largely of multi-year ice. In recent years first-year ice has come to dominate the southern Beaufort Sea, so we replaced the 1976 statistics with data from a winter 2007 survey of the same region by the submarine HMS “Tireless”. Holding other scour geometry parameters constant, we calculated new return periods and burial depths and found large changes which appear to be reflected in the results of recent resurveys of regions subject to ice scour. We reflect on the likelihood that these more moderate conditions will continue to prevail in the future.