mean diameter of 0.17 mm. The study investigated scour depths associated with 

 various wave conditions, beach slope, seawall locations, and seawall 

 inclination. The more significant findings of this study included: 



a. Maximum scour is approximately equal to the deepwater wave height 

 for the range of conditions tested. Wave steepnesses ranging from 

 0.003 to 0.036 were run for the cases where the seawall was at a 

 90-deg (vertical) inclination. 



b. Maximum scour for seawall location occurs in the range of 

 0.5 < X s <0.67, with X s as previously defined. 



c . Maximum scour depth increases with an increase in wave height. 



d. Maximum scour depth decreases with a decrease in the angle of 

 inclination of the seawall, or a decrease in the angle the face of 

 the seawall makes with the horizontal. 



e . Maximum scour depth decreases with a decrease in beach slope. 



Field Studies 



44. Sato, Tanaka, and Irie (1968) also presented field data obtained 

 following a storm which significantly scoured foundations fronting the 

 seawalls at the Port of Kashima. These data supported the findings listed in 

 paragraph 42, particularly the finding that maximum scour depth, S max , is less 

 than or equal to the deepwater significant wave height H so . The measured 

 scour depths at seawalls showed that maximum scour depth under storm 

 conditions was nearly equal to the maximum significant deepwater wave height 

 H so observed during the storm. 



45. Sawaragi and Kawasaki (1960) compiled field data on erosion in 

 front of seawalls at eight sites in the Sea of Japan. The data obtained 

 covered a period during which the seawalls were impacted by three significant 

 storms. Analysis of the data led to the conclusion that the maximum depth of 

 scour is approximately equal to the wave height in deep water, and that the 

 location of maximum scour is related (proportional) to the location of the 

 point of breaking of incident waves. 



46. Sexton and Moslow (1981) obtained data along seawall-backed beaches 

 at Seabrook Island, South Carolina to examine scour and subsequent recovery 

 following the September 1979 attack of Hurricane David. The beach in front of 

 one concrete seawall experienced a scour depth of 2.1 ft and overtopping also 

 caused some scour on the landward side of the seawall. Since maximum deep- 

 water wave heights exceeded this value considerably, the S d /H < 1.0 rule of 

 thumb is apparently supported here as well. 



44 



