Ice ridge keel characteristics and distribution in the Northumberland Strait

Ice ridges impacts are a major design consideration for offshore structures in the Arctic. Consequently, field programs on the frequency and characteristics of ridges can provide valuable empirical information for the design of future offshore structures. The Confederation Bridge ice force monitoring program monitors ice ridge keels through sonar instrumentation at the bridge. A total of 3199 keel cross-sections were identified during the 2007 and 2008 ice seasons using a new processing method. Of the 3199 keels identified, 137 keels caused loads over 1 MN. The shape of each keel was visually identified and classified as one of four shapes: triangular, trapezoidal, w-shaped, and multiple peak keels. Triangular and trapezoidal keels made up more than 60% of the keels that cause loads over 1 MN. Four of the five largest loads had keels that were trapezoidal. For the 3199 keel cross-sections, the depth, width, leading and trailing keel angles, bottom width and area were identified and distributions of these keel properties were developed. The distribution was then compared to the design keel depth distribution from the Confederation Bridge. The observed 2007 and 2008 keel depth distributions was slightly lower than the design distribution likely due to the significant number of multiple peak and w-shaped keels. Additionally, the maximum keel depth suggested by the observed distribution was shallower than the maximum predicted keel depth.

► We examined two years of sonar records in Northumberland Strait. ► We characterized ridge keel shapes, introducing new forms of keels. ► We prepared statistics of ridge keel dimensions and the relations between them. ► We compared the ridge keel depth statistics with those used in the design.