TWO-DIMENSIONAL TESTS OF WAVE TRANSMISSION AND REFLECTION 

 CHARACTERISTICS OF LABORATORY BREAKWATERS 



by 

 William N. Seelig 



I . INTRODUCTION 



The primary function of a breakwater is to reduce wave heights in an area 

 being sheltered. Breakwaters are primarily used to protect harbors from 

 excessive wave action, to prevent beach erosion, and to trap sediment for 

 mechanical bypassing at an inlet or harbor entrance. A secondary use of 

 breakwater design is to reduce the wave reflection from the structure. 

 Reflected waves combined with incident waves can produce undesirable water 

 motions that may be a nuisance to navigation or encourage scour at the toe of 

 a structure. 



Since the cost of building breakwaters is generally high, methods are 

 needed to estimate transmitted and reflected wave heights to enable comparison 

 of alternative structure designs. This report presents suggested methods for 

 predicting transmission and reflection characteristics of breakwaters based on 

 laboratory experiments, including the work of previous investigators. These 

 methods supplement Section 7.23 of the Shore Protection Manual (SPM) (U.S. 

 Army, Corps of Engineers, Coastal Engineering Research Center, 1977). The 

 basic types of breakwaters considered are permeable and impermeable structures 

 with crest elevations above the Stillwater level (subaerial) and below the 

 Stillwater level (submerged) . The other factors investigated include wave 

 height, period, breakwater cross-section design, and material characteristics. 

 Both monochromatic and irregular waves were tested. 



Section II of this report presents a brief review of research conducted 

 by previous investigators. Section III describes the laboratory setup and 

 procedures; Sections IV, V, and VI present data analysis methods and definitions. 

 The conditions tested are summarized in Section VII. Detailed descriptions of 

 the breakwaters tested and materials used are given in Appendixes A and B; 

 summary tables and figures of laboratory results are presented in Appendixes 

 C, D, and E. 



Laboratory results are used in this study to develop a method for predicting 

 wave transmission by overtopping coefficients using the ratio of breakwater 

 freeboard to wave runup (suggested by Cross and Sollitt, 1971) and the break- 

 water crest width (suggested by Saville, 1963). The wave transmission by 

 overtopping prediction method is then combined with the model of wave trans- 

 mission through permeable structures of Madsen and White (1976) and this 

 combination package is verified with the laboratory results over a wide range 

 of conditions. Prediction methods are summarized in the computer programs 

 OVER and MADSEN (Apps. F and G) . An example breakwater design is worked with 

 the aid of the two computer programs to illustrate how the prediction methods 

 can be used to compare alternative breakwater designs, and to illustrate the 

 importance of various design parameters. 



II. LITERATURE REVIEW 



Some of the important sources of ideas and data used in preparing this 

 report are summarized below in chronological order. 



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