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|Title:||Transmission of wave energy through and overtopping of the Long Beach, California breakwater : hydraulic model investigation|
|Authors:||Port of Long Beach.|
Hales, Lyndell Z.
Water wave energy
Water wave experiments
Long Beach Harbor
Water wave transmission
|Publisher:||Hydraulics Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; H-76-10.|
Abstract: In order to meet growing future demands, a 10- to 15-yr harbor expansion program for the ports of Los Angeles and Long Beach , Calif., has been designed to provide an increased amount of terminal space and berthing areas. This increased space will be developed by dredging and landfill construction in the Outer Harbor, with the landfill proposed to lie parallel with the San Pedro Bay middle breakwater for approximately 18,500 ft (14 ,000 ft being in the Long Beach jurisdiction), leaving a 1,000-ft-wide channel between the breakwater and the landfill. Concern over the resulting wave conditions existing in the channel predicated an agreement between the City of Long Beach, Calif., and the U. S. Army Engineer Waterways Experiment Station (WES) to conduct two-dimensional wave flume tests to experimentally determine the resulting wave climate in the channel for a range of wave periods and wave heights at different tidal elevations. The experimental breakwater was subjected to this range of wave conditions and the amount of wave energy transmission through and overtopping of the breakwater was recorded at specific locations within the channel. Results are presented in both graphical and tabular form. As part of the U. S. Army Engineer sponsored study of the Los Angeles-Long Beach Harbor complex, deepwater wave characteristics approaching the area were propagated numerically into shallow water (to the breakwater) and the effects of refraction and shoaling were determined. The transmission coefficients obtained from this experimental study then were applied to these data, and estimations of the magnitude and duration of specific waves occurring in the channel were developed. Conclusions reached from the study include : (A.) A physical model of the Long Beach breakwater should be constructed at a scale larger than about 1/40 for the range of wave characteristics deemed significant in order to eliminate potential scale effects. The scale chosen (1/36) was sufficiently large to eliminate any scale effects in the measured data. (B.) The fundamental mode of the free oscillation of the channel section has a period of 44 sec. Resonance (surging or seiching) of the navigation channel due to surface gravity waves penetrating or overtopping the breakwater with periods up to 19 sec should not be significant. A partial standing wave system does exist in the channel, however, as can be noted by the fairly large variation in wave height between stations for some test conditions. (C.) For an initial wave height of constant period generated at different tide elevations, the higher tide level resulted in more energy transmission, although in some cases the amount of increase was not statistically significant. (D.) The transmitted wave height was a function of initial wave height, period, and tide elevation. This function was experimentally determined to be the relationship displayed in Figures 6-13. (E.) Tide elevation probably is not a major parameter until overtopping of the structure occurs, at which time a large amount of energy is allowed to enter the navigation channel. This observation was also noted by Walther and Lee during prototype field studies. (F.) Walther and Lee reported transmission coefficients of 0.30 for waves with periods of around 17 sec. This experimental investigation showed that transmission coefficients varied between 0.07 and 0.46, depending on incident wave period, wave height, and tide elevation. For the conditions reported by Walther and Lee, this study indicates values of 0.26 to 0.28 for the transmission coefficient; therefore, their prototype data are considered to be in agreement with results of this investigation.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Miscellaneous Paper|
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