beach eroded back to the end of the tank and marked reflection started to 

 occur, influencing bar shape. 



267. Comparison with a field measurement . Initial speeds of bar 

 movement in the LWTs had the same magnitude as observed in the field measure- 

 ments of Sallenger, Holman, and Birkemeier (1985) made during a storm at 

 CERC's FRF at Duck, North Carolina. In general, morphologic features of the 

 profile in the field showed rapid response to changing wave conditions, in 

 qualitative agreement with profile response generated in the LWTs. The bar 

 crest at Duck had an average offshore speed of 2.2 m/hr during the initial 

 phase of one storm (6-hr average) and a speed of 1.4 m/hr for another storm 

 which had smaller waves. Migration speeds measured by Sallenger, Holman, and 

 Birkemeier (1985) were close to those obtained in the CE and CRIEPI studies 

 for the cases showing strong erosion (Figures 23b and 23d) . 



268. The distance between the location of the maximum trough depth and 

 the bar crest was approximately constant during cases with a well -developed 

 trough. Coarser grained beaches tended to have greater distances between 

 trough bottom and bar crest. Larger waves also caused the distance from the 

 bar crest to the trough bottom to increase for a specific grain size. For a 

 typical unibarred profile, the vertical distance between maximum trough bottom 

 and bar crest appeared to increase slightly with time up to the equilibrium 

 value . 



Distance from break point to trough bottom 



269. According to the (small-scale) wave tank results of Miller (1976), 

 the trough located shoreward of a breakpoint bar is initiated where the 

 breaking waves completely disintegrate. Sunamura (in press) made the observa- 

 tion that this process is valid not only for plunging breakers but also for 

 spilling breakers, although the trough is not so marked and takes longer to 

 form under spilling breakers. The distance between break point and plunge 

 point may thus be generalized to include both plunging and spilling breakers 

 to yield a plunge distance. Galvin (1969) noted through small-scale and 

 prototype-scale experiments that this distance was equal to about 4H^, . For 

 the CRIEPI data, Sunamura (in press) related the distance between trough 

 bottom and break point to bottom slope and wave steepness at breaking. In the 

 relationship, distance was normalized by deepwater wavelength, which gives the 



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