47. Walton and Sensabaugh (1979) examined field data associated with 

 scour which was observed in Panama City, Florida following Hurricane Eloise in 

 September 1975. From their observations, it was noted "that "apparent" 

 seawall scour observed at Panama City . . . was considerably less than the 

 maximum predicted by the rule of thumb." Additionally, the authors stated 

 that "most seawalls with cap elevations less than 10 ft above grade 

 experienced a maximum of 2-3 ft of scour." This observation was for 

 unprotected beaches which fronted seawalls in the area studied. 



Scour Prediction at Submerged Pipelines 



48. Another situation where scour presents a design problem for coastal 

 engineers and oceanographers is the case of scour around submerged pipelines. 

 For additional discussion of this problem, the reader is referred to Chao and 

 Hennessy (1972), Herbich et al . (1984), and Hales (1980). Chao and Hennessy 

 developed a method for estimating order of magnitude maximum scour depth under 

 offshore pipelines. The method is based primarily on 2-D flow theory and 

 makes use of certain reasonable assumptions, including infinite pipe length, 

 and scour occurring when the velocity in the scour hole is greater than the 

 free stream velocity. Refer to Figure 16 for identification of symbols and 



Pre- Scour 

 Condition 



Figure 16. Pipeline scour problem as described by Hennessy and Chao 



45 



