(generally precast concrete) have been tested extensively, but usually 

 for stability purposes. Runup results for concrete units are discussed 

 in Section V,2,b. 



(1) Permeable Structures . Details of quarrystone rubble-mound 

 structures, for which data by various authors were reanalyzed, are given 

 in Figure 24. Test conditions are given in Table 7. 



Hudson (1958, 1959) tested a breakwater configuration using a wide 

 range of slopes and wave conditions. The tests were done principally 

 for one stone size, with a smaller stone tested for the 1 on 4 and 

 1 on 5 slopes. In the tests with the smaller stone, results for the 

 1 on 5 slope seemed to give anomalously high runup values, and are not 

 discussed here. 



The structure geometry used by Hudson (1958) is shown schematically 

 in Figure 24. The core is below the SWL and its height-to-water depth 

 ratio is approximately 0.75, with only armor stone above the top of the 

 core. The structure slope used in analyzing the relative runup is the 

 slope above the core level; below the top elevation of the core, the 

 structure slope is steeper, being 1 on 2 for upper slopes of 1 on 3, 

 1 on 4, and 1 on 5 (see Fig. 24). The effects of this nonplanar slope 

 on runup are unclear. Heights of waves breaking on the structure would 

 certainly be modified (increased or decreased) relative to a planar 

 slope, depending on the effects of the steepened structure on shoaling. 



Runup curves based on data by Hudson (1958) are shown in Figures 

 25, 26, and 27. The points shown in the figures are not Hudson's data 

 points but are values interpolated from his data for the particular 

 wave conditions noted in each figure. The graphs are differentiated 

 by relative depth, dg/H^, and the corresponding relative stone size, 

 H^/kp, where k r for stones is the nominal stone diameter. 



Jackson (1968a) conducted limited tests on a rubble-mound breakwater 

 using "rough" quarrystone and also stone essentially the same as Hudson's 

 (Jackson's "smooth" quarrystone). Jackson's structure differed, however, 

 in having a core slightly above the SWL (see Fig. 24). If the second 

 underlayer is included in the core height (underlayer stone weight = 

 W/200, where W is the armor stone weight) then the core height is 

 approximately 1.1 dg, whereas Hudson's core height was « 0.75 dg. 

 Jackson's structure would be expected to reduce wave transmission with 

 a consequent increase of both runup and reflection. This conclusion is 

 supported by the available data; e.g., Jackson's runup data are approxi- 

 mately 8 percent higher than Hudson's for a 1 on 1.5 slope, ds/H^ = 5.0. 

 Figure 28 gives example runup curves derived from Jackson's data for 

 smooth quarrystone; the relative depth is dg/H^ = 5.0. 



Savage (1958, 1959) tested permeable slopes with relatively small 

 diameter stones. His structures differed from Hudson's and Jackson's 

 in that the stone "structure" was placed against the vertical tank wall. 

 Wave transmission through the structure was not possible; therefore, 



61 



