Sand Beaches 



195 



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Figure 1 70. Highest swash mark, scour around pebble, and elongate markings in the backwash lee of holes and other 

 irregularities on Scripps Beach. Ocean is at bottom. 



the saturated lower part of beaches and at 

 angles of slope between 2 and 10°. They 

 also found that the angle at the apex of the 

 rhombs becomes progressively smaller with 

 increased velocity of backwash, as predicted 

 by Woodford. The next most common are 

 erosional ripples — best developed on beaches 

 that have pronounced laminations (Fig. 172). 

 These ripples are broad, 30 to 60 cm, and are 

 steeper where they cross the outcropping 

 dark laminae. They have the appearance of 

 a series of small cuestas and evidently are 

 produced by erosion, possibly therefore they 

 appear mostly during spring tides. Wind 

 ripple marks are frequently present on the 

 beach and are readily identified by their usu- 

 ally angular trend with respect to the beach 

 and their presence on the backslope of a 

 berm. Water ripple marks are unusual; cur- 

 rent ripples do occur but rarely anywhere 

 except at the mouths of bays (Fig. 173). 

 Symmetrical wave ripple marks have not 

 been reported, except of course on the under- 

 water extensions of the sand beaches where 

 they have been described by Inman (1957). 

 At low tide when the beach water table 

 intersects the beach surface less than 1 meter 

 above the low sea level (Fig. 118), much wa- 

 ter drains from the sand. Runoff across the 



saturated lower part of the beach produces 

 intricate badlands topography in miniature 

 which would leave no question about orien- 

 tation if seen in the geological column. Fre- 

 quently, the water carries so much sand that 

 it forms a braided pattern and builds a delta 

 that progresses across the beach, obliterating 

 previous minor features (Fig. 173). In some 

 instances the sand also appears to flow en 

 mass somewhat like a mudflow. 



A larger feature present on sand beaches 

 as well as on gravel beaches is the berm. 

 Several sets may sometimes be observed. 

 Although the observation is not well docu- 

 mented, it is beheved that berms on sand 

 beaches are more numerous in the early fall 

 than at other times of the year because they 

 form periodically during the spring and 

 summer and are removed by storm waves 

 during the winter. Their origin is not well 

 understood, but one possible mode of for- 

 mation is that started by cutting of the 

 beach at spring tide so that a scarp a frac- 

 tion of a meter high is left. As waves at 

 later high tides reach higher and higher on 

 the foreshore, they finally cross the top of 

 the scarp and deposit their load of sand. 

 In time a landward-sloping surface develops, 

 a berm. Once established, a berm tends to 



