For the case of Pier 400 Berth 408, there is a wave gage labeled San Pedro Buoy located approximately 6 NM offshore of the proposed berth operated by Scripps Institution of Oceanography where measurements have been made hourly since 1998. These data were used along with other additional data sources to characterize the deep water wave climate. The wave height cumulative frequency of occurrence at San Pedro Buoy is illustrated in the following Graph.

The rationale for utilizing deep water wave data as the initial source of wave characteristics is that waves in deep water can be considered typical over a fairly wide section of the coast and these waves have not been modified by propagation over shallow water. The next step in characterizing the wave climate at the project site is to transform the deep water waves to the project site to incorporate the wave transformation resulting from wave refraction and shoaling caused by the decrease in water depths near shore, reflection from the shoreline of coastal structures such as breakwaters, wave diffraction around coastal structures, and wave transmission through the breakwater protecting the Port of Los Angeles. This wave transformation process is typically accomplished using a computer model of wave propagation which incorporates calculations for all of the pertinent processes.

The latest technology in wave transformation models was used to transform the measured deep water waves to Pier 400. The particular model used was developed by the Danish Hydraulic Institute and is classified as a Boussinesq wave model. Characterization of the deep water wave climate along with the results of the wave transformation modeling provide the wave characteristics in the following table at the berth as classified as operational with a typical occurrence on an annual basis. The highlighted column indicates the worst case scenario of the operational wave climates. The ranges of wave heights at the berth are the minimum, average, and maximum wave height over the berthed ship footprint.

Similarly, extreme wave characteristics typically occurring only once in several years are characterized in the following table.

The wave height estimates above are the average of the highest one third of the waves in the irregular wave train, commonly referred to as the significant wave height. The significant wave height for an irregular wave train is typically what the casual observer would estimate the wave height to be and is a commonly accepted term for characterizing the wave height.

In addition to the normal and naturally visible ocean waves, there is a class of ocean waves called infragravity waves which are very long waves with periods ranging from 50 to 200 seconds. These waves have very small amplitudes and are not normally visible to the naked eye, but they can cause harbor oscillations and resonance with subsequent movement of moored vessels capable of causing excessive mooring line loads. These long period waves were evaluated using the latest technology long wave model developed for the Ports of Los Angeles and Long Beach. The results of this modeling work were used in the dynamic mooring analysis for the berth availability analysis.

The numerical modeling of the wave transformation was verified for the proposed marine oil terminal by wave measurements made as part of the design studies. Two wave gages were installed for a 29-day period adjacent to Face C of Pier 400, which is the location of the proposed berth on the western side of Pier 400, and adjacent to face D. The locations of the wave gages are illustrated in the figure below. The water depths for the wave gages were 21 meters Mean Lower Low Water (MLLW) and 24 meters MLLW for Face C and Face D, respectively. The gages were configured to measure waves every 4 hours over the 29-day period.

The wave climate during the measurement period of August 2005 indicated that the waves along Face D were substantially higher than along Face C as would be expected with the mean wave heights for combined wind waves and ocean swell of 0.12 meters and 0.56 meters for Face C and Face D, respectively. A summary of the significant wave heights along Face C is illustrated in the graph below. Locally generated wind waves were typically present during afternoon sea breeze conditions and caused the peak period to vary substantially. These wind waves also caused a great deal of variation in the wave direction.

A filter was applied to the wave data to eliminate wind waves with periods shorter than 6.7 seconds from the wave spectra since the longer period waves provide a more accurate measure of the wave climate to be used for analysis of ship motion since ships do not typically respond to waves of such short periods. Comparison between the filtered wave data and deep water wave data from San Pedro Buoy located outside of the harbor indicated generally good agreement between offshore wave periods and wave periods adjacent to Pier 400. The average filtered significant wave heights over the monitoring period were 0.09 meters and 0.17 meters for Face C and Face D, respectively. Comparison between the deepwater wave data and the filtered wave data at the berth indicated very good agreement with the wave transformation model.