622 SAND-MOVEMENT ON THE NEW SOUTH WALES COAST, 



dominant influence,* and its direction indicates the course which 

 sand and shingle will take on the beach: but when the range is 

 comparatively small and the current due to it weak, the littoral 

 drift or the eddy currents, caused by projecting headlands, will 

 control the movement. If this, in its turn, should also be weak, 

 then the prevailing winds may set up surface currents which will 

 determine the direction and rate of sand-travel. It is possible 

 also that one of the causes mentioned may so interfere with 

 another that the results become very difficult and often impossible 

 to trace. 



The accompanying chart of part of the Pacific Ocean 

 (Plate lii.) shows a bifurcation of the drift-current due to the 

 South-East trade winds, about 800 miles off the coast of Queens- 

 land. The northern part of this current flows through Torres 

 Straits into the Arafura Sea, and thence to the Indian Ocean; 

 and the southern portion, with which we are immediately con- 

 cerned, strikes the Australian coast about Moreton Bay. It is 

 here deflected to the southward and follows the east coast of New- 

 South Wales as a stream current until it meets the north-easterly 

 current of the South Pacific, when it is again deflected, this time 

 to the east, and then again to the north along the western coast 

 of New Zealand. 



In the offing the average speed of this current is about one- 

 half to one knot, so that per se it is not a powerful stream. Its 

 surface-speed is increased by a northerly or north-easterly wind; 

 and a southerly gale lasting for more than twenty-four hours will 

 often temporarily reverse the direction for a period depending 

 upon the force of the gale and its duration. 



As before stated, the coast of New South Wales is fairly 

 .straight, the salient points not projecting into the ocean far 

 enough to cause any serious disturbance of the current. Some 

 of them, however, whilst exposing a concave side to the north, 

 are sufficiently prominent to cause deflections or counter currents 



* Haupt, L. M., " Littoral Movements of the New Jersey Coast," Trans. 

 Amer. Soc. Civil Engineers, Vohxxiii., 1890. 



