Erosional Profile 



Figure 3. Erosional and depositional profile shapes 

 (after Komar 1983) 



steepness are the most important wave parameters controlling beach profile 

 change. Wave steepness is defined as H /L , in which H is the deepwater 

 wave height and L is the deepwater wave length. In linear wave theory, 

 L = gT 2 /(2T) , in which g is the acceleration of gravity, and T is the 

 wave period. 



17. Johnson found that the critical wave steepness for delineating 

 depositional and erosional profiles was in the range of 0.025 to 0.03. 

 Higher steepness values result in erosion; lower values cause deposition. 

 For example, a 2-m-high, 8-sec-period wave (H /L = 0.02) implies a 

 depositional profile; whereas a 2-m-high, 6-sec-period wave (H /L = 0.036) 

 results in an erosional profile. In this example the wave height is 

 constant, and the period is different. Combinations of wave height and 

 period are not completely random. Although higher waves usually have longer 

 periods, storm waves typically change from high steepness, short-period waves 

 to lower steepness, long-period waves as the storm passes. 



18. Other factors affecting profile change include the beach grain 

 size (Iwagaki and Noda 1963) or fall velocity (Dean 1973), mean beach slope 

 (e.g., Sunamura and Horikawa 1975, and Hattori and Kawamata 1981), and 

 magnitude of the wave height (Saville 1957). Hallermeier (1984) has recently 

 presented a classification of the occurrence of nearshore deposition and 

 erosion through use of a sediment mobility number and the Ursell number. 

 Each of the above cited papers has examined or presented one or more criteria 

 for predicting the tendency to form either an erosional or depositional 



prof i le . 



10 



