488 REPORT— 1891. 



From the above it may be imagined that most artificial 

 harbom'S are surrounded by many perils, and a person design- 

 ing one ^^'ho does not recognise the striking peculiarity of the 

 New Zealand coasts lays himself open to serious risks of 

 failure. Similarly, any engineer carrying New Zealaiid ex- 

 perience and applying it to another country without further 

 investigation w^ould be liable to grievous error. Thus the only 

 positions in New Zealand where harbour-works could be con- 

 structed without risk from drifting materials would, on this 

 theory, be the ends of each Island projecting in the direction 

 whence the currents and prevailing winds come ; but in 

 another country under different conditions of prevailing winds 

 and waves the favourable positions for such structures would 

 be quite different. 



Persons who have not studied these phenomena are very 

 apt to misinterpret the conditions which they observe, and 

 draw wrong conclusions from them. Thus, some persons 

 think that there being deep water in front of a headland is 

 sufficient evidence that it stops the travel of the beaches : they 

 argue that if sand or shingle did pass round there must neces- 

 sarily be a beach round the bluffs, and all the bays on the lea 

 side would be filled up, whereas no changes are observed. 

 They foi'get that the material carried away is always equal to 

 the supply, therefore all things remain as they were ; no effect 

 can be seen unless you follow the stream to some place where 

 there is a total change of conditions, and there a vast deposit 

 will probably be revealed. 



I have known people suggesting various positions for 

 breakwaters or harbours : one position was to keep the material 

 entirely back, another would have the effect of " shooting it 

 off" to some place of safety, and so on. But the fact remains 

 that if there is an obstruction to the travel of the beaches the 

 material will travel round it regardless of the direction in 

 which it is placed. Sooner or later the stream will lap round 

 it and fill up the sheltered space. 



In this perplexing condition of things the only means 

 VN'hich appears to offer a chance of safety is to imitate nature 

 as closely as possible — that is, to place the entrance of the 

 artificial harbour so that it may be swept by the full force of 

 the wave, and give every facility for the sand and shingle 

 which travels past the entrance to continue its journey. To 

 have the entrance swept by the vvaves requires that it should 

 be at right angles to their prevailing direction, and that the 

 side of the enclosure in which the entrance is be in the direc- 

 tion of the prevailing heaviest waves. This may make a 

 dangerous entrance, but there is no other way out of the diffi- 

 culty that I know of. 



Another way to deal with the travel of beaches is to enclose 



I 



