A NEW NONDIMENSIONAL NUMBER FOR THE ANALYSIS OF WAVE REFLECTION FROM RUBBLE-MOUND BREAKWATERS

Full scale measurements of the reflection performance of a rock island breakwater were obtained using an array of 6 pressure transducers, bo th before and after a reduction of the seawards slope of the structure , This slope reduction (1:0.82 to 1:1.55) effectively reduced maximum reflection coefficients by 15%. Comparisons of reflection coefficients with various surf-similarity parameters including the Iribarren and M iche numbers failed to provide an accurate parameterization of wave re flection for both data sets, Multiple regression analysis indicated th at the shortcomings of the available surf-similarity parameters can be attributed to an overemphasis of the effects of the incident wave hei ght (H-i) and the structure slope (tan beta) relative to the wavelengt h (L). On the basis of the regression analysis a new non-dimensional r eflection number R = d(t)L(0)(2)tan beta/HiD2 is postulated here, whic h revises the relative weightings of these parameters, and introduces other physically significant parameters, including the local water dep th at the toe (d(t)), and the characteristic armour diameter (D). This reflection number more effectively parameterizes wave reflection for these data, and for the first time provides the basis for a new scheme for the prediction of reflection coefficients (K-r) based entirely on the analysis of full scale data, where; K-r = 0.151 R(0.11) or K-r - 0.635 root R/(41.2 + root R).