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MODELING LONGSHORE TRANSPORT AND COASTAL EROSION DUE TO STORMS AT BARROW, ALASKA

PECKHAM, SCOTT D  INSTAAR, Univ. of Colorado.
Syvitski, James PM  INSTAAR, Univ. of Colorado.

Coastal erosion and the associated risk to homes and structures is a major concern for the residents of Barrow, Alaska. During two unusually large storms in August of 2000 and October of 1963, there was little or no sea ice for a distance of over 360 miles from shore. This large fetch, combined with winds of over 30 mph that were sustained for more than 16 continuous hours, resulted in observed wave heights of 10 feet and very high longshore sediment transport rates. These wave heights are in close agreement with what would be predicted for a fully-developed sea created by a 30 mph sustained wind. Using the equations that describe a fully-developed sea state, semi-empirical longshore transport equations can be recast in terms of sustained wind speed and breaker angle. This reformulation shows that the longshore sediment transport rate is highly nonlinear and varies as the sixth power of sustained wind speed. This helps to explain why there is such a large difference in sediment transport rates for wind speeds of say 20 mph vs. 30 mph and helps residents of Barrow to assess risk from wind speed data. It also shows that storms from the west, like the two under consideration, have breaker angles close to 45 degrees near the city of Barrow. This is the breaker angle that results in the maximum sediment transport rate. Theory predicts that a nodal point should occur in the immediate vicinity of Barrow, such that such storms will result in coastal erosion south of Barrow and deposition or little change for the coast just north of Barrow. Preliminary results for a coastal erosion model that incorporates these results will be presented.


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