CHAPTER V. 



FETCH, EXPOSURE, AND WAVE-POWER. 



Definition of " Fetch "Fetch alone no indication of. exposure Wheeling of 

 waves Direction of waves affected by contours of sea-bed Exposure of sites 

 affected by shift of wind and by scour during gales Glacial action mistaken 

 for wave-power Movement of earth's crust in relation to apparent effects of 

 wave-power Eaised beaches Euins of temple of Jupiter Serapis Effect of 

 waves on coast near Wick ; also at Holburu Head, Caitli ness Effect of falling 

 wa ter Evidences of wave-power in Zetland Wave-power as displayed at 

 Ymuiden, Kurrachee, Wick, Alderney, Scilly Isles, Wolf Rock lighthouse, etc., 

 Mud as an indication of exposure General remarks on exposure of sites. 



Fetch and Exposure. The distance over which waves may 

 be driven by the wind to any particular point, is called the 

 " fetch " to which such a point is exposed. Thus we say that 

 a harbour is exposed, between certain limits, to a fetch of so 

 many miles ; by which is meant the distance, within such limits, 

 to the opposite or windward shore, or to barriers, such as rocks 

 or shoals, capable of stopping or interrupting the free run of 

 the waves. In other words, " fetch " means the distance in any 

 direction which can be freely traversed by undulations in the 

 course of their development. 



It is obvious that fetch, in itself, cannot be taken as the 

 measure of the exposure of any site. 



It may happen that gales never blow on the line of longest 

 fetch, whereas heavy rollers may wheel round a point or head- 

 land which might have been expected to afford shelter. More- 

 over, gales and storms have bounds which vary in different 

 localities, and which practically limit the effective length of 

 fetch. 



The harbour at Kurrachee is open to a fetch of 500 miles, 

 and the depth of water is such as to admit of heavy waves 



