A NEW Wave Transmission
FOR Submerged Breakwaters
Harry C. Friebel, US Army Corp of Engineers, Philadelphia, PA USA, Harry.C.Friebel@usace.army.mil
Lee E. Harris, Ph.D., P.E., Florida Institute of Technology, Melbourne, FL USA, LHarris@fit.edu
1. WAVE TRANSMISSION MODELs
Recently attention has been focused upon a category of breakwaters classified as submerged breakwaters. Increasing interest in utilizing submerged breakwaters and artificial reefs for shoreline stabilization requires accurate predictive models and relationships for predicting wave attenuation. The object of this study is to develop a two-dimensional (2D) model as an improvement to existing wave transmission coefficient models.
The majority of wave transmission models for submerged breakwaters are derived from physical modeling. The data are analyzed and a wave attenuation model is empirically formulated. For this study, the data from five physical model studies were used to derive a new wave transmission model utilizing all available experimental data. The five data sets that were combined and analyzed were from: Seelig (1980), Daemrich and Kahle (1985), Van der Meer (1988), Daemen (1991), and Seabrook (1997); yielding a total of 799 wave transmission measurements. Ahrens (1987) data set was excluded from the model formulation due to variations in structure crest heights during testing.
2. A NEW TRANSMISSION MODEL
A new wave transmission model was successfully developed from an empirical, statistical analysis, while attempting to keep the primary physical processes associated with submerged breakwaters intact. The model was subjected to graphical inspection, compared to existing submerged breakwater transmission models, and governed by the number of independent variables incorporated.
The dimensionless variables represented in the model are believed to accurately represent the dominating physical processes associated with the wave transmission process. The results confirm that the transmission coefficient is highly dependent upon the ratio of the freeboard to the incident wave height, and the relative width and height of the structure. The ‘best fit’ model with a RSQ value of 0.94 and a standard deviation of 0.05 is shown in Figure 1.
The proposed model provides improved predictions of wave transmission than previous models, while using only non-complex, dimensionless variables. The model results from a simple and understandable theory, maintaining the importance and influence of the physical parameters. The proposed model produces optimized results for accurately predicting wave transmission over an extensive range of design conditions. The model is suggested as an engineering aid for the design of submerged breakwaters.
Figure 1 - Model Results Compared to Data
Ahrens, J.P., 1987. “Characteristics of Reef Breakwaters.” Technical Report CERC-87-17, Coastal Engineering Research Center, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, 62.
Daemrich, K.F. and Kahle, W., 1985. Schutzwirkung von Unterwasserwellenbrechern unter dem einfluss unregelmassiger Seegangswellen. Eigenverlag des Franzius-Instituts fur Wasserbau und Kusteningenieurwesen, Heft 61.
Seabrook, S.R., 1997. Investigation of the Performance of Submerged Rubblemound Breakwaters, M.Sc. Thesis, Queen’s University, Ontario, Canada, 200.
Seelig, W.N., 1980. “Two-Dimensional Tests of Wave Transmission and Reflection Characteristics of Laboratory Breakwaters.” T.R. 80-1, Coastal Engineering Research Center, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, 187.
Van der Meer, J. W. and Daemen, I. F. R., 1994. “Stability and Wave Transmission at Low-Crested Rubble-Mound Structures.” Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE. Vol. 120, 1-19.