Therefore, the tribar relative roughness of this problem is the 

 same as tested by Jackson, for which results are given in Table 11. 

 For cot 9 = 1.5, dg/H^ = 5.0, and HJ,/k r = 2.86, r tr>ibar « 0.44. 

 However, this problem requires an answer for dg/H^ = 3.0; lacking 

 further information, r =s0.44 will be used in this problem. The 

 results of various investigations referenced in this study indicate 

 that r is not necessarily constant for changing H^/k r values or 

 changing dg/H^ values; thus, assuming here that r is a constant 

 0.44 is simply a best estimate. The chosen r value is applied to 

 the applicable smooth-slope relative runup value. For the wave 

 conditions and structure slope corresponding to this problem, 

 smooth-slope relative runup is, from Figure 14, 



= 1.82 



° smooth. 



The estimated relative runup on this tribar- cove red rubble mound is 

 then 



w\ = r (h) 



1 rough \ ° I smooth 



= (0.44) (1.82) 



= 0.80 



1 rough 



The runup on this rubble mound is 



R -{k) 



(H') 



rough 

 = (0.80)(3.4) 

 R w 2.7 meters (8.9 feet) . 



Evaluation of possible scale effects is discussed in Section VI. 

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



3. Stepped Slopes . 



Stepped-slope configurations have been tested for use in low-energy 

 wave climates. Field construction techniques vary, but include case-in- 

 place steps, such as in Harrison County, Mississippi, and soil-cement 

 stepped surfaces (Nussbaum and Colley, 1971). Laboratory tests have 

 been performed on precast, interlocking stepped blocks (Jachowski, 1964), 

 on impermeable steps (Saville, 1955) and on soil-cement stepped slopes 

 (Nussbaum and Colley, 1971). Saville's tests were conducted with the 



96 



