60. For seawalls constructed in areas where -0.011 < h y ,/L < 0.05 and 

 0.015 < H < 0.06, 



-^ = J22.12 h u /L + .25 (66) 



is recommended for determining ultimate scour depth. For all other cases, the 

 S max /H < 1 rule of thumb should be appropriate for determining ultimate scour 

 depth at vertical walls . 



Submerged Pipelines 



61. The method developed by Chao and Hennessy (1972) for estimating 

 order of magnitude maximum scour depth under offshore pipelines is fairly 

 straightforward and should provide reasonable predictions. Herbich (1981) 

 used Chao and Hennessy 's method to develop a series of charts that can be 

 conveniently used to estimate bottom scour for various combinations of 

 sediment size, bottom current velocity, and pipeline diameter. 



55 



