CHARACTERISTICS OF SOLITARY WAVE BREAKING INDUCED BY BREAKWATERS By Stephan T. Grilli, 1 Member, ASCE, Miguel A. Losada, 2 and Francisco Martin 3 ABSTRACT: Laboratory experiments are presented for the breaking of solitary waves over breakwaters. A variety of behaviors is observed, depending on both breakwater and incident wave height: for emerged breakwaters, wavesmay collapse over the crown, or break backward during rundown; and for submerged break- waters, waves may break forward or backward, downstream of the breakwater. The limit of overtopping and wave transmission and reflection coefficients are experimentally determined. It is seen that transmission is large over submerged breakwaters (55-90%), and may also reach 20-40% over emerged breakwaters. Computations using a fully nonlinear potential model agree well with experimental results for the submerged breakwaters, particularly for the smaller waves (Hid < 0.4). For emerged breakwaters, computations correctly predict the limit of over- topping, and the backward collapsing during rundown. INTRODUCTION Emerged breakwaters are designed to offer protection on their seaward face (armor layer), by inducing runup, breaking, and partial reflection of incident waves. Extreme waves, however, may overtop the structure and break on its upper part (crown or crest) or on its landward face. Hence, both of these must have proper reinforcements (e.g. crown wall). When overtopping occurs, a transmitted wave may reform and still cause damage shoreward. Submerged breakwaters are designed to offer protection by inducing breaking and partial reflection-transmission of large waves. For both breakwater types, assuming no structural damage, the percentage of wave transmission can be used as a measure of the degree of protection offered by a breakwater against a given wave climate. In the present study, laboratory experiments and fully nonlinear com- putations are carried out and compared for the transformation, breaking, overtopping, and transmission of solitary waves over submerged and emerged breakwaters. Solitary waves are believed to represent a good model for tsunamis (Goring 1978) and also for extreme design waves because of their large runup, impulse, and impact force on structures. The propagation and runup of solitary waves over shelves and slopes has been the object of numerous studies. Among these, we will mention the works by Goring (1978) and Pedersen and Gjevik (1983) using Boussinesq equations, and by Synolakis (1987) and Kobayashi et al. (1987, 1989) using NSW equations. Based on the latter model, Kobayashi and Wurjanto (1989, 1990) calculated monochromatic wave overtopping, and wave transmission, over emerged and submerged trapezoidal breakwaters, respectively, and found reasonable agreement with laboratory experiments and empirical for- 1Assoc. Prof., Dept. of Oc. Engrg., Univ. of Rhode Island, Kingston, RI 02881. "-Prof., Univ. of Cantabria, Santander 39005, Spain. 3Grad. Student, Univ. of Cantabria, Santander 39005, Spain. Note. Discussion open until July 1, 1994. To extend the closing date one month, a written request must be filed with the ASCE Manager of Journals. The manuscript for this paper was submitted for review and possible publication on February 25, 1991. This paper is part of the Journal of Waterway, Port, Coastal, and Ocean En- gineering, Vol. 120, No. 1, January/February, 1994. 9 ISSN 0733-950X/94/ 0001-0074/$1.00 + $.15 per page. Paper No. 1428. 74