Then from Figure 40, for a riprap structure, 



§T* 0.92 

 n o 



R = (0.92) (H^) 



= (0.92)(1.2) 



R =1.1 meters (3.6 feet) 



Figure 40 is derived from large-scale experiments, and no correction 

 for scale effects is necessary (discussed further in Sec. VI) . 



************************************ 



************* EXAMPLE PROBLEM 10 ************* 



GIVEN : Rubble-mound structure using two randomly placed layers of tri- 

 bars for protection; cot 6 = 1.5; g = 0; dg = 10.0 meters; H^ = 3.4 

 meters (11.2 feet); T = 6.2 seconds; h a « 10.0 meters; k r « 0.7 

 meter (2.3 feet), where k r is the length (height) of a tribar leg. 



FIND: Determine runup. 



86; -f-** 1.0 



SOLUTION: 









Hi 



-- 2.94 «3.0; ^~ 



Kp 





gT 2 ' 



3.4 





(9.81)(6.2) 2 



0.009 



This structure is similar in design (high core) to the rubble-mound 

 breakwater tested by Jackson (1968a) for which r values are given 

 in Table 11. However, r values are not listed for tribars for 

 the condition of H^/k p = 4.9. An estimate of r is necessary. 

 Relative roughness in Table 11 is specified for a particular rela- 

 tive depth, dg/H^, = 5.0. For dg/H^ = 5.0, the relative roughness 

 in this problem would be 



h; 



o / 1 \ / d s 



kv, do/... / \k 



/h- 



5 / \0.7 



H' d 



r^= 2.86, for £= 5.0 . 



95 



