MISCELLANEOUS NOTES. 



Height of Waves. The height of the waves to which an exposed 

 entrance may be subjected will depend upon the greatest fetch or reach 

 of open sea, and will closely approximate to the square root of the 

 distance from the windward shore. The following formula by the 

 late Mr. T. Stevenson, gives, with sufficient accuracy for all practical 

 purposes, the height of waves due to long distances and heavy gales, 

 and where the water is of sufficient depth to allow of waves being 

 fully formed. 



h = l'5j~d 



When h = height of waves in feet, d = length of exposure in 

 miles. 



It is, however, to be observed that, for short fetches, in narrow 

 waters or arms of the sea, waves are raised higher during very 

 violent gales than the above formula indicates, although it does not 

 appear that the waves go on increasing in the same high ratio for any 

 considerable distance. The following formula will therefore be more 

 exact for short distances and heavy squalls. 



h = 1-5 Jd + (2-5 - ~ 



The table on page 408 shows comparatively the height of waves 

 for different lengths of fetch, calculated from the above formula. 



There are several other causes besides the direct effect of fetch, 

 which may tend to influence the height of waves in front of an 

 exposed entrance, and which it is necessary to take into consideration, 

 such as alterations to existing works, or in the natural surroundings. 

 The following may be considered as some of the principal of these 

 causes. 



(a) The removal of a spending beach by building a quay, or an 

 embankment of any kind across it by which an area, over which 

 waves may break and disperse, is lost. 



(6) Deepening the entrance channel or the tidal basin itself, thus 

 the difficulty of keeping vessels at their moorings alongside the quays 

 of a harbour during flood- tide is increased. 



