CURRENTS. 71 



per hour. The speed of the current past the end of Dover pier 

 was similarly increased as the structure advanced; indeed, it 

 is not possible to project a close pier far into the sea without 

 thus increasing the velocity of the littoral currents. 



Pier-heads are very liable to be undermined or eroded by 

 such currents, and it is often necessary to make special provision 

 to guard against injury from this cause. 



Currents will generally be found to run in a pretty direct 

 course along a coast from headland to headland, those within 

 such lines being often irregular, and partaking more or less of 

 the nature of eddies. 



A good deal of misconception exists about littoral currents, 

 and they are not sufficiently distinguished from the run, or set 

 along a shore, resulting from wave action, or from the temporary 

 currents set up by wind. There is no doubt that imaginary 

 littoral currents are very often credited with the transport of 

 material along a shore, the movement of which is almost wholly 

 attributable to wave action. 



I do not wish it to be understood that those currents, where 

 they exist, do not, under certain conditions, play an important 

 part in the transport of material along a coast; but, excepting 

 in cases where their velocity is considerable, it will be found 

 that they play an insignificant part as compared with wave 

 action, which I believe to be the chief agent at work in the 

 movement of beach drift. 



The foregoing remarks do not refer to the flood and ebb 

 currents running into and out from the tidal compartments of 

 rivers and estuaries. 



There is scarcely any point in connection with sea-works 

 which requires more careful attention than that of littoral drift 

 and the forces by which it is regulated. 



When strong currents are opposed by wind waves, the latter 

 are increased in height, and often break and cause a dangerous 

 sea. On the other hand, a current flowing in the same direction 

 as the waves will tend to run them down, as will also a strong 

 current running parallel to the waves. I was told, when at 

 Scrabster, that the rapid current through the Pentland Frith 

 shelters the roadstead there to some extent from northerly swell, 

 excepting, of course, at slack water. 



Captain William Campbell gave corroborative evidence on this 

 point before the Royal Commission on Harbours of Refuge in 



