therefore, 



: s _ 10 



3.1, 



and 



3.2 



= 0.065. 



Interpolation from the SPM, Figure 7-12 is: 

 B_= 2.4. 



Scale correction from the SPM, Figure 7-13 is 1.14. 

 Table 2. Wave runup on revetment. 



Revetment 



Smooth 



Roughness 

 coefficient 1 



Scale 



Type 



R'/H- 



R 



correction 



Riprap 



1.37 



4.4 



2.4 



0.5 



1.14 



Gabion mats 



1.50 



4.8 



2.4 



0.55 



1.14 



Lok-Gard blocks 



2.60 



8.3 



2.4 



0.95 



1.14 



Tire mats 



1.78 



5.7 



2.4 



0.65 



1.14 



1. Appendix. 



Step 5, 



Toe-Scour Depth : The maximum toe-scour depth below the 

 natural bed is about equal to the height of the maximum 

 unbroken wave that can be supported by the original depth 

 of water (SPM, ch. 5) . 



The minimum water depth at the revetment toe is 4 feet; 

 maximum water depth is 10 feet. The design wave at the toe 

 of/ the structure is 5 feet which is a breaking wave in 

 4.75 feet of water. 



Therefore, since a breaking wave at the structure toe 

 is possible, the maximum estimated depth of scour would be 

 5 feet below the natural bed. This estimate does not con- 

 sider structure shape or wave reflection properties and is 

 probably quite conservative. 



Assuming scour is less for sloping revetments with low 

 reflection coefficients, the following estimates of scour 

 depth are developed (Table 3). 



16 



