Tides 



131 



. SANDSTONE 



AREA STUDIED 



JOINTS FOR MEASURING DEPTH 

 TO WATER TABLE 



BEACH SAND PROFILE 



r^ 



-TIDE CURVE 



"15" 



1400 1600 



TIME 



WATER-TABLE PROFILES OF EL SEGUNDO BEACH 



VERTICAL X 12 



APRIL 19. 1947 



EBB TIDE 

 FLOOD TIDE 



Figure 1 1 8. Positions of water table in sand beach at El Segundo. Note phase lag of water table behind that of tide 

 curve of open sea. From Emery and Foster (1948, Fig. 1). 



currents that on the open shelf theoretically 

 reach their maximum between high and low 

 tide, that is, at ebb and flood stages. In this 

 region the tidal currents rarely exceed 20 

 cm/sec and, owing to earth rotation, the 

 tidal current of the open shelf should change 

 direction clockwise so that it makes a com- 

 plete sweep around the compass in about 



12.4 hours. Boundary conditions near the 

 shore and at the bottom confine the tidal 

 current largely to directions parallel to the 

 shore and bottom contours. In addition, 

 currents induced by winds commonly are 

 great enough to mask those produced by 

 tides (Fig. 119). 



A quite diff"erent effect is believed by 



