<- 1 x \ v « 



..,„ L„M'"' 



^ Imagff^ary i 



xiiform slooe 











h , \ 













XV 



'2 







c 1 ) 















Figure 10. Composite cross-section proposed by Sawaragi (1966) 



31. Based on a study by Eckert (1983), toe scour protection should be 

 designed to accommodate the maximum scouring force that exists where wave 

 downrush on the structure face extends to the toe. According to Eckert 

 (1983) , the rule of thumb for minimum toe scour protection will be inadequate 

 if the following conditions are present: 



a. The water depth at the toe of the structure is less than twice the 

 height of the maximum unbroken wave height that can exist in that 

 water depth. 



b . The wave reflection coefficient exceeds 0.25, which is generally 

 true for structures having slopes steeper than 1 on 3 . 



32. Movable bed model tests conducted by Lee (1970, 1972) on a 

 quarrys tone -armored jetty with a slope of 1 vertical on 1.25 horizontal 

 indicated that adequate toe protection was provided by a double layer of rock 

 having mean weight W on , given by 



W aPI on = ^a/30 (42) 



where W a is the mean weight of individual primary armor stone, lb f , as 

 determined from Equation 39. In addition, tests showed that the width of the 

 toe protection should be equal to the width of four to six of the stones 

 having the mean weight given by Equation 42, and could be estimated by the 

 following: 



B. 



= n„ k. 



P/ = 



Yr 



1/3 



(43) 



In the above , B 



is the apron width in feet, n is the number of stones, 



and k A is a layer coefficient varying between 0.94 and 1.15, dependent upon 

 armor type, shape, and construction method as detailed in the Shore Protection 

 Manual (1984), and 7 r is the unit weight of armor stone, lb f /ft 3 . 



30 



