Coastal Erosion Responses for Alaska - the National Sea Grant ...

Coastal Erosion Responses for Alaska: Workshop Proceedings 27
Ocean waves
The essential reason for interest in the wind regime stems from its capacity to
drive other systems that directly impact the coast. Waves, sea level changes
(surges), and ice movement are of primary concern here. A preliminary examination
of seasonal wave energy totals for the circumpolar region underscored
the importance of sea ice in moderating ocean waves. Specifically, it showed
that (a) heavy ice will reduce seasonal wave energy totals, and (b) trends in
sea ice conditions are as important as trends in strong wind (and storm) frequency.
This was shown by wave energy trend results for the southern Beaufort
Sea coast, where trends from wind alone suggested a slight decrease in wave
energy; but the addition of sea ice trends, which are decreasing at a faster rate,
indicated a net increase of wave energy.
Storms
Trends in storm activity, with “storm” being objectively defined by an algorithm
working with wind-speed, were instructive by the lack of strong trends spanning
many decades. Instead, the more important point here is that the time
series are characterized by periods of higher and lower activity. The length
of cycles differed: Barrow has moved through one cycle, while Bethel seems
to exhibit higher-frequency of cycling (Fig. 2). Another interesting observation
from the Barrow time series is that, in the last 20 years, the number of
events occurring in the “open water” season (July-December) has increased
with respect to the number of events in the “freeze-up” season (January-June).
This represents a departure from the first 30 years of record, during which the
two had been roughly equal.
Conclusions
The three main points to take away regarding sea ice are (a) its reduction opens
up the coast to greater erosion threat from storms, (b) its inherent variability
means that a return to heavier ice conditions, at least temporarily, is likely,
and (c) model predictions of future patterns at the local scale are not immediately
forthcoming, especially for land-fast ice. Regarding wind patterns, some
trends are noted, but large differences are noted as a result of station location.
Exposed coastal sites can be far windier than relatively sheltered sites only a
few miles away. Seasonal totals of coastal wave energies are very dependent on
sea ice conditions, both concentrations during a given season as well as trends.
Storm event counts showed no long-period trends, but instead exhibit cycles
of activity with periods lasting several years to several decades.