Coastal Processes

Waves: The Pacific Northwest is well known for the severity of its wave climate (Tillotsen and Komar, 1997) with deep-water significant wave heights and periods averaging 3.0 m (9.8 ft) and 12 s respectively in the winter.  The largest storm recorded by the Grays Harbor buoy occurred on 3 March 1999.  Deep-water wave heights exceeded 9.0 m (29.5 ft) for over 5 hours, peaking at 10.6 m (34.8 ft) and accompanied by a storm surge of 1.4 m (4.6 ft) forced by sustained 80 km/hr (49.7 miles/hr) winds.  The result of this storm was widespread coastal flooding throughout the littoral cell, particularly in Ocean Shores where several houses were damaged and a public restroom was destroyed.

Maintaining a database of the environmental forcing responsible for beach change and variability is critical for modeling future shoreline positions and quantifying the probability of coastal flooding.  Fortunately there are national networks of both wave and water level gages maintained by various outside agencies, e.g., the Coastal Data Information Program (CDIP), the National Data Buoy Center (NDBC), and the National Ocean Service (NOS), that make data available via the internet.  However, time series of wave direction, which are often the most vital to shoreline change models, are typically available either over a limited duration or not at all.  Currently, there are three operational buoys within the littoral cell (Grays Harbor bar, Columbia River bar, Cape Elizabeth).  However, these buoys alone can not resolve the variation in wave climate along the coast.  Therefore, models that consider the alongshore distribution of wave energy are being used in conjunction with available buoy data (see SWAN).

Seasonal changes in environmental forcings influence seasonal cycles in beach response.  In the CRLC, seasonal variability in wave height and direction generally results in northerly offshore sediment transport in the winter and southerly onshore sediment transport in the summer.  The CRLC is meso-tidal with a 2.0 to 4.0 m (6.6 to 13.1 ft) range and winter water levels along the coast are as much as 0.3 m (0.98 ft) higher than the summer water levels.


Water levels in the Columbia River littoral cell.  Mean values (red line) were calculated since 1980.



Wave height in the Columbia River littoral cell. Mean values (red line) were calculated since 1981.

Sea Level: Interannual climatic variability also affects waves and water levels, which in turn can influence beach response.  The winter of 1997/1998, the first winter of the monitoring program, coincided with one of the largest El Niņo events of the 20th century.  In the Pacific Northwest, strong El Niņos feature increased frequency of extreme waves from the south-southwest and higher than normal sea levels (Komar and Good, 1989).  During the previous major El Niņo that occurred in 1982/1983, large wave heights and acute wave angles forced excessive offshore and northerly sand transport, causing severe beach erosion and shoreline orientation change that persisted for several years (Peterson et al., 1990).  During the 1997/1998 El Niņo event the CRLC experienced mean water levels up to 40 cm higher than typical, mean winter wave heights up to 1.0 m higher than usual, and wave directions from a steeper southerly angle (Kaminsky et al., 1998).  The following two figures show the increase in monthly mean values for both significant wave height and period, respectively. 

February, the month with the largest waves, featured wave heights 1 m higher than normal with wave periods over 1 s greater than normal.  During the months of January and February 1998 there were 13 storm events in which the significant wave height reached or exceeded 6 m.  The figure below shows that from summer through fall 1997 waves approached the coast from a more acute southerly angle than typical.  This change in environmental conditions resulted in increased deposition of sediment along the northern boundaries of each of the sub-cells.  Longer-term climate change signals are also evident in wave and water level data.  A recent study by Allan and Komar (2000) suggests that wave heights have increased by almost 1.0 m off the Washington coast in the last three decades.


Wave periods for the Columbia River littoral cell.  Mean values calculated since 1981.


Wave direction for the Columbia River littoral cell.  Mean values calculated since 1993.


References

  1. Allan, J.C. and P.D. Komar, 2000.  Spatial and temporal variations in the wave climate of the North Pacific, Report to the Oregon Department of Land Conservation and Development, 46 p.

  2. Kaminsky, G.M., P. Ruggiero, and G. Gelfenbaum, 1998.  Monitoring coastal change in southwest Washington and northwest Oregon during the 1997/98 El Niņo, Shore & Beach, pp. 42 - 51.

  3. Komar, P.D. and J.W. Good, 1989.  Long-term erosion impacts of the 1982-83 El Niņo on the Oregon coast, Proceedings of Coastal Zone ’89, pp. 3785-3794.

  4. Peterson, C.D., P.L. Jackson, D.J. O’Neill, C.L. Rosenfeld, and A.J. Kimerling, 1990.  Littoral cell response to interannual climatic forcing 1983-1987 on the central Oregon coast, USA, Journal of Coastal Research, 6, No. 1, pp. 87-110.

  5. Tillotsen, K.J. and P.D. Komar, 1997.  The wave climate of the Pacific Northwest (Oregon and Washington): A comparison of data sources, Journal of Coastal Research, 13, pp. 440-452.

Ecology - SEA Program | USGS - Coastal & Marine Geology

This is http://www.ecy.wa.gov/programs/sea/swces/research/coastal_processes.htm
Maintained by CMAP, Washington Department of Ecology
Address questions and comments to George Kaminsky
Modified 22 Mar 2012