Extreme Wave Heights In The Gulf Of Alaska

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Abstract Expansion of Outer Continental Shelf (OCS) leasing into frontier areas like the Gulf of Alaska has been accompanied by a need for more complete environmental design data such as extreme wave characteristics and seismic risk. The U.S. Geological Survey (USGS) recognizing this need, has instituted programs to gather such information. The results of one of these programs, extreme wave data, are presented herein. Extreme wave heights due to severe extra tropical storms have been estimated for three deep water locations in the Gulf of Alaska. These estimates are based on hindcasts of the wave climatology for the entire North Pacific Ocean. Wave statistics were compiled for a thirteen year period from 1964 to 1977. An analysis of these statistics yielded extreme wave height as a function of return period. The wave characteristics were computed using the Spectral Ocean Wave Model (SOWM) at the U.S. Navy's Fleet Numerical Weather Central (FNWC). This model was found to be applicable for wave estimation in this area through a favorable comparison between computed and measured wave heights using data taken at several Pacific locations. The results of this study confirm the severe winter wave climate of the Gulf of Alaska. Although predicted extremes for this area are somewhat greater than those predicted for the North Atlantic and the North Sea they are not as great as have been predicted recently by other investigators. Two of the three locations are sufficiently close to the present offshore lease areas in the northeastern Gulf that deepwater wave estimates for these locations would provide the initial conditions for design wave estimation for offshore structures in this region. Introduction Petroleum industry interest in the Gulf of Alaska, particularly in the northern continental shelf has been strong. The Department of Interior scheduled a sale for the summer of 1969; however, this was cancelled because of heightened environmental concerns following the January, 1969 Santa Barbara oil spill. The second call for nominations in November, 1974 resulted in even stronger interest than the first and a lease sale was conducted in April, 1976 (OCS Lease Sale 39). The approximate location of the lease area is shown in Figure 1. The expansion of OCS leasing into frontier areas like the Gulf of Alaska has been accompanied by the need for more complete environmental design data such as extreme wave characteristics and seismic risk data. Up to the present time practically no data have existed in the public domain with which judgments could be made relative to the adequacy of structures intended for service in the Gulf of Alaska. Inherent to the basic responsibilities of the U.S. Geological Survey for OCS leasing is the specification of requirements which must be met by offshore operators in the design, construction or operation of fixed or mobile facilities in these regions. These requirements are currently promulgated through OCS orders developed by the USGS.