Artificial islands are being used in the Beaufort Sea to conduct exploratory drilling for hydrocarbons. By May 1977, 15 islands had been built in water depths ranging to the 5 fathom isobath (8.5 m). Ice up to about 7 ft (2 m) thick covers the Beaufort Sea for 9 months of the year and has a considerable influence on construction methods and island design. The islands need sufficient sliding stability to withstand the forces generated by the moving ice; and the possibility of ice ride-up has to be considered. Islands can be built either during the winter by trucking gravel over the ice or in the short arctic summer using dredges. Temporary slope protection is needed to avoid beach erosion during the short summer months. Slope protection is designed to match the measured and predicted sea state, which also influences the island freeboard needed to avoid wave overtopping. Slope protection methods include anchored polyfilter cloth, sandbags and sacrificial beaches. Optimum island designs have to account for constructional constraints, working area needed, ice action, wave action and geotechnical factors.