456 
SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
straight. The bigger waves are broken off far out in the sea due to the shallow 
beach profile. Thus they scour the sea bed and throw up sand to form a barrier 
bar. With the appearance of the sand bar above the water, normally parallel 
to the beach, a lagoon is formed. The Negombo lagoon with its straight coast 
line is an excellent example of a coastline of emergence. 
The dynamics of Negombo beach 
There is some conflict of opinion about the origin of the material from which 
an off-shore bar is made. This aspect is of great importance when one attemps 
any beach protection work. Gilbert advocates the theory that the material 
comes from longshore currents, while the opposite view, critically examined 
by Johnson, is in favour of De Beaumont’s theory that the major part of the 
material is derived from the ocean floor, as is evidenced by the fact that the 
seaward side of the bar tends to overdeepen. Most bars are not continuous, but 
are interrupted by openings commonly called tidal inlets. It is noted that the 
Fig. 2