the welding has taken place (Figs. 30 and 31). The relict runnel which 

 forms on the upper ridge surface after welding is analogous to a berm 

 runnel. Small sand ridges continue to move across the upper ridge 

 surface at high tide, gradually filling in the runnel. For several days 

 after welding, the active high tide beach face continues on the backshore; 

 however, as the berm increases in size, the frequency of high tide swashes 

 over the berm diminishes until what was originally the ridge beach face 

 becomes the active high tide beach face. This change marks the transi- 

 tion from an early postweld profile to a late postweld stage. The time 

 of the change in beach- face location at PL-0 is marked by an X in 

 Figure 24. 



3. Postweld Period . 



At the beginning of the postweld period on 13 July, profiles PL-0 

 through PL-3 had attained welded berms with steep beach faces; profiles 

 PL-4 through PL-8 had a wide low tide terrace with scattered small ridges; 

 and profiles PL-9, PL- 10, and PL- 11 were intermediate in development, with 

 moderately large ridges nearing the welding stage (Figs. 32 and 33). The 

 period between 13 July and 12 August was characterized by relatively low- 

 energy conditions. A typical late postweld beach profile at PL-0 is 

 shown in Figures 34 and 35. A large welded ridge where the mean high 

 water mark is below the surface of the berm is a characteristic of the 

 late postweld profile. A wide low tide terrace may also exist where 

 numerous small ridges are common. In time and with the absence of high- 

 energy conditions, a gradual seaward migration of the beach- face surface 

 will occur as successive, seaward-dipping beds are lain on the beach-face 

 surface. The result of noninterrupted accretion on the beach face from 

 22 July until 14 August is shown in Figure 35. There is a gradual de- 

 crease in the beach face gradient from 27 July, primarily as a result of 

 a decrease in wave steepness and breaker power for this period (Fig. 24) . 

 Because of this decrease in wave activity during the later part of the 

 study, accretion outweighed erosion, especially between Pl-4 and PL-10. 



Figures 36 and 37 show changes in beach morphology immediately after 

 the welding of the large ridge between PL-0 and PL-3. The small ridges 

 at PL-5, PL-6, and PL- 7 on 13 July migrated quickly across the low tide 

 terrace and welded before 20 July (Fig. 33) . The northern end of the 

 study area assumed a mature profile after the welding of the ridge at 

 PL-8 by 20 July. The erosion-deposition map for 20 July (Fig. 36) shows 

 that welding has occurred at PL-4 and PL-8, as indicated by the vertical 

 accretion of 50 to 100 centimeters of sediment. The accretion at profile 

 PL-6 is due to the formation of deltalike lobes of sediment on the runnel 

 surface (Figs. 38, 39, and 40). This sediment lobe is probably caused by 

 profiles PL-6 and PL-7 which are lower than the adjoining profiles; there- 

 fore, greater scour will occur as water empties from the runnel resulting 

 in a deepened runoff channel. As the tide begins to flood, sediment is 

 carried through the runoff channel and is deposited. Later, as the higher 

 parts of the ridge adjacent to the runoff channel are flooded, residual 

 currents keep the migrating ridge from assimulating the sediment lobe. 

 Eventually, the lobe is overlapped by a ridge (Figs. 41 and 42). 



48 



