Abstract

In the period March through August, 1973, sea ice movement was observed off Barrow, Alaska, on the Chuck chi Sea coast with a land based radar. It is concluded that during the breakup period, July and early August, the ice movement is predominantly determined by ocean currents parallel to the coast and that grounded features are significant to the maintenance of the shore fast ice during breakup. Stress measurements in the shore fast ice during March and April indicate that temperature and tidal variations can contribute significantly to the stress distribution in the grounded shore fast ice. These findings are significant to the design of Off-shore structures.

1. Introduction

The development of the coastal resources in Northern Alaska is impeded throughout most of the year by the presence of significant quantities of sea ice. Annual sea ice may reach a thickness of 2 meters; beyond the shore fast zone, it is continually in motion, driven by the forces of wind, ocean currents, and internal ice stress. Multi-year ice, because of its greater strength and thickness, also presents a hazard, as do pressure ridges. Safe marine transportation along the Arctic coast of Alaska is limited to a brief period in the summer when a narrow strip of open water between the shore and the pack ice is available for marine access to coastal development projects. During the winter, the region immediately adjacent to the coast is covered with relatively immobile fast ice, presenting an unknown hazard to off-shore structures and terminal facilities. In the foreseeable future, exploratory oil wells will be drilled in the fast ice zone of the Beaufort Sea, and the fast ice will exert significant stresses upon the off-shore structures to be used.

As a preliminary means of determining such stresses, a program was begun two years ago. The objectives were the development of the instrumentation necessary for in-situ stress measurements in the ice, and the accumulation of information on the stresses encountered in the fast ice. These objectives were met during the past year. Furthermore, the installation of a land-based radar produced a detailed record of the activity of the pack ice and the fast ice during the breakup period. The site chosen for the field measurements was Barrow, Alaska (156°40'W, 71°20'N) because of the excellent research facilities that are available at the Naval Arctic Research Laboratory (NARL). The logistic support of NARL, together with the financial support of NOAA-Sea Grant Program and the Alaska Oil and Gas Association, were essential to the program. Results include a continuous record of in-situ stress in the fast ice. Because of the wide variation in sea ice motion and properties from year to year, several year's accumulation of such informationis necessary to permit the prediction of sea ice motion in the vicinity of fast ice, and the stress in fast ice itself. One then may be in a position to develop realistic design criteria for safe and economical off-shore structures.

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