SWELL PROPAGATION AND NEARSHORE WAVE CLIMATE
Douglas Scott1, Donald Resio2 and Cristobal Pantoja3
1. Baird & Associates, Ottawa, Ontario
2. U.S. Army ERDC, Vicksburg, MS
3. Baird & Associates, Santiago, Chile
1.
INTRODUCTION
A detailed study of swell wave conditions in the southern Pacific Ocean has been performed with particular
emphasis on the western Southern American coastline. This study was one part of an overall wave hindcasting
investigation undertaken for the Servicio Hidrografico y Oceanogrfico de la Armada de Chile (SHOA) to define the
inshore wave climate at various locations along the Chilean seabord.
Considerable coastal infrastructure has been developed in Chile over the last two decades, and the impetus for this
study was based on concerns with the lack of consistency utilized in the coastal engineering design process,
beginning with, but not limited to, the definition of the wave conditions. The available wave records in Chile are of
very limited duration, thus many designers rely on a variety of wave data sources ranging from ship observations to
hindcast wave data of various types and flavours. One of the major issues identified was that engineering structures
have often been developed using data with relatively simplistic wave definitions, employing integrated wave
parameters, such as the characteristic wave height (Hm0), peak wave period (Tp) and the mean wave direction
(MWD). As will be shown in this paper, the wave climate in Chile is complex and it is important that appropriately
complex wave analysis techniques be employed.
It has also been long recognized in Chile that swell waves are a critical consideration in assessing the performance
of ports, and several of the ports in Chile do experience downtime due to excessive vessel motion induced by long-
period swells and harbour resonance phenomenon. An important consideration is the ability to estimate the
In support of this study, a forty-year wave hindcast was completed for the Pacific Ocean using a 2nd Generation
wave model and the NCEP/NCAR Re-Analysis wind fields. Some of the key wave modelling challenges addressed
included:
Undertaking a long-term wave hindcast in data-poor environment.
The appropriate reproduction of the wind fields in intense extratropical cyclones of the Northern and
Southern Pacific Ocean.
The simulation of swell propagation using wave models having limited directional resolution.
This paper summarizes the methodology and findings of the study.
2.
REGIONAL SETTING
Chile is a long, relatively thin country that stretches along the western edge of the Southern American continent, as
may be seen in Figure 1. It experiences large meteorological variability along this length. The climate varies from
arid desert in the north at latitude 17 S to a much colder and wetter environment in the south at latitude 56 S. An
important topographic feature is the presence of the Andes mountain chain that runs down the eastern edge of the
country. In the northern half of the country, atmospheric circulation is largely controlled by the South Pacific High,
resulting in winds blow parallel to the coast north of approximately 31 S. Further south, the winds take a more
westerly direction. In the zone of sub-Antarctic depressions (south of ~42), average wind speeds increase
considerably and there is a more complete western dominance to the wind direction.
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