Hovever, observations have clearly established that high, steep waves tend 

 to erode fine beach sediment, while low, steep waves tend to cause beach 

 accretion. Quantitative classifications of the occurrence of eroded versus 

 accreted beaches have benefited from an increasing data base and from better 

 developed analyses of profile formation processes. The two classifications 

 presented here have some established pertinence to processes at prototype 

 scale. 



Early laboratory experients indicated that the type of waveformed profile 

 was determined by deepwater wave steepness (deepwater significant wave height 

 (Hq) / deepwater wave length (Lq)). With prototype-scale tests, Saille (1957) 

 established that the wave height was as important as wave steepness in 

 determining profile type. Extending this work, by considering a fundamental 

 sediment characteristic, the fall velocity (see Ch. 4, Sec. 11,1), Dean (1973) 

 reported that the profile type depended on the parameter 



H 

 F = ° 



o V^ T 

 where 



F = dimensionless fall time parameters 



Hq = deepwater significant wave height 



Vj = fall velocity of particles in the water column 



T = wave period 



Beach erosion usually occurred for F > 1 , and beach accretion usually 

 occurred for F < 1 . This classification is supported by laboratory tests 

 at reduced and at prototype scales (Dean, 1973; Kohler and Galvin, 1973). 



Sunamura and Horikawa (1974) considered average nearshore bottom slope 

 (tan ) and reported shoreline changes at various field sites in an 

 independent classification of profile types. The occurrence of beach erosion 

 or accretion vras reported to depend on the parameter 



-0.67 



where Gq is a dimensionless parameter for determining accretion or erosion 

 and dcQ is the size of the 50th percentile of sediment sample. For the 

 field data, beach erosion usually occurred for G < (1/18) , and beach 



accretion usually occurred for G > (1/9) . These calculations used maximum 



wave height between shore surveys, wave period corresponding to this height 



2 

 for L = (g T /2 ) , mean subaerial grain size for d^Q , and average slope 



between the shoreline and a water depth of about 20 meters. The numerical 



values of G for beach erosion or accretion in small-scale laboratory tests 



were reported to be somewhat different than in field shoreline changes, but 



this may have been due to the calculation suppositions for field cases. 



4-85 



