tests, little effort was made to verify its use in field or larger scale 

 applications . An additional concern is that the equation yields decreasing 

 scour depths with increasing values of K r . This is directly in contrast to 

 results obtained by other researchers, including Herbich et al. (1984), 

 Chesnutt and Schiller (1971), and Xie (1981). Because of these limitations 

 and apparent discrepancies, Equation 55 is not recommended for use in field 

 applications . 



Other Laboratory Studies to Investigate Scour at Seawalls 



42. Sato, Tanaka, and Irie (1968) studied scour in front of seawalls 

 for both normal and storm beach profiles. In their study, seawall inclination 

 (angle face of seawall makes with horizontal), grain size, beach slope, and 

 wave conditions were varied using monochromatic waves in a 2-D facility. They 

 identified five different types (modes) of scour described below as: 



Type 1 - Rapid initial scour followed by a gradual accretion of material 



Type 2 - Rapid initial scour leading to beach stability 



Type 3 - Rapid initial scour giving way to slower, but more prolonged 

 erosion 



Type 4 - Continuous gentle scour 



Type 5 - Continuous gentle accretion 



In addition to identifying the different scour modes , they reached the 

 following conclusions: 



a. Relative scour depth (S,j/H ) can be larger than unity for flatter 

 (non- storm) waves, but for storm waves with steepness between 0.02 



and 0.04, the relative scour depth was equal to unity. 



b. Relative scour depth decreased with decreasing relative median grain 

 size, (d 50 /H o ). 



c. Maximum scour depth for storm waves occurred when the wall was 

 located at either the shoreline or just landward of the plunge 

 point. 



d. Maximum scour depths occurred for the Type 3 classification of 

 scour, which is characterized by rapid initial scouring that gives 



way to slower, more prolonged erosion. 



e . Maximum scour depths occurred for seawall inclinations of 90 deg 



(vertical) and initial beach slope had little effect for the range 

 of conditions tested. 



43. Chesnutt and Schiller (1971) conducted approximately 50 tests in 

 two different wave flumes to investigate scour in front of seawalls along the 

 Texas Gulf Coast. The sand used in their study was Texas beach sand having a 



43 



