sediment sizes is between -0.5 and 1.9 phi, so that for velocities less 

 than 15 centimeters per second little or no entrainment will take place; 

 for the size of particles, velocities greater than 24 centimeters per 

 second are necessary for erosion to take place. Figure 12 reveals how 

 infrequently these velocities were attained. 



IV. SUMMER BEACH MORPHOLOGY 



1. Introduction . 



Changes in beach morphology within the study area between 2 July and 

 12 August can be divided into two major periods of activity. The initial 

 or preweld period covers the time before and up to the welding of a large 

 ridge on 12 July. Although smaller ridges were migrating shoreward in 

 other parts of the study area, a large ridge and runnel system extending 

 from profile PL- 3 to a point 350 meters south of profile PL-0 was the 

 site of the most dynamic changes in beach morphology within the study 

 area (Fig. 13). Between 13 July and 12 August, accretion was due to 

 numerous ridges of different sizes and locations migrating landward 

 across the low tide terrace, eventually welding on the backshore. The 

 changes in beach morphology during this period comprise what may be 

 considered a postweld period. Hayes and Boothroyd (1969) discussed low 

 tide beach morphology relative to the occurrence of northeasterly storms, 

 and defined the following stages of beach morphology that are broadly 

 applicable to this study. 



a. Early poststorm; the profile is flat to concave and beach surface 

 is generally smooth and uniformly medium grained. 



b. Early accretion; small berms, beach cusps, and ridge and runnel 

 systems form rapidly. 



c. Late accretion or maturity; landward-migrating ridges weld onto 

 the backshore to form broad, convex berms. 



Characteristic preweld profiles PL-0 and PL-5 for 2 July are shown 

 in Figures 14 and 15. Profile PL-0 approximates the conditions at PL-1, 

 PL-2, and PL-3, or the southern end of the study area. A typical profile 

 of the southern end consists of a large ridge (average height 80 centi- 

 meters) which migrates landward during high tide. The large berm at PL-0 

 with a steep high tide beach face and a slope varying between 9° and 10°, 

 is more characteristic of a later stage of maturity of a poststorm beach 

 profile than the berm at profile PL-5. Although ridge and runnel systems 

 are at both profile locations, the large berm and nearly welded ridge at 

 PL-0 are indicative of a nearly welded beach profile. Other profiles 

 (PL-5 through PL- 8) which do not have a broad berm exist contemporaneously 

 with profiles such as PL-0. The ridge has not migrated as far landward on 

 these profiles, resulting in a wider runnel and low tide terrace; the 

 beach-face slope varies between 6° and 8°. Profiles PL-5 and PL- 11 are 

 shown in Figure 15, with PL- 11 representing the northern end of the study 



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