of as an accretionary feature. The berm typically forms above the still -water 

 level but may extend below the water surface and move the shoreline position 

 slightly seaward as it grows with time. The vertical extent of the berm is 

 closely related to the runup limit, whereas its shoreward extent in the 

 equilibriiom state is mainly determined by how the grains move under gravita- 

 tional force. The point on the foreshore where berm formation is initiated 

 mainly depends on the runup limit where a larger runup implies berm initiation 

 further shoreward. Runup is essentially a function of local beach slope, wave 

 period, and breaking wave height for both regular waves in the laboratory 

 (Hunt 1959, Savage 1959) and irregular waves in the field (Holman and 

 Sallenger 1985). 



284. No information about runup was available from the CRIEPI experi- 

 ments and only little information from the CE experiments. In the CE experi- 

 ments, runup was measured in most cases, typically for the first 10-20 waves 

 (Kraus and Larson 1988a) . There were only five CE cases which had berm build- 

 up and measurement of runup. However, an indication of the relationship 

 between berm formation and runup may be obtained by viewing Figure 28 where 

 the distance to the mass center of the berm is plotted as a function of the 

 runup length l^ , all quantities referenced to the initial still -water level. 

 The runup length is the average of all runup measurements, and the first 

 profile survey (typically performed after about 1 hr of wave action) was used 

 to calculate the distance to the berm center of mass. The distance to the 

 center of mass was roughly half the runup length which, if the berm is 

 considered to be approximately symmetrical, indicates that the runup length 

 was close to the shoreward end of the berm, as would be expected. All berms 

 in the previously-mentioned five cases were formed on profiles showing a 

 strong tendency for onshore transport during the full duration of the run, 

 although a small breakpoint bar may have been present. 



285. In cases where a berm was present but the transport rate was more 

 variable in direction both along the profile and in time, the berm was often 

 small and sometimes formed with its center of mass below the still -water 

 level. Equilibrium properties of the berm on such profiles (berm volume, 

 maximum berm height) were reached very rapidly, typically prior to the time of 

 the first profile survey. 



107 



