XXXI 



situated over 4,000ft. outside of Entrance 

 Island ; it is really a semicircular shoal of 

 sand, extending from the north shore to 

 the rocky peninsula on the south side, 

 with a depth of about Sft. Gin. in the line 

 where steamers pass out, but the depth 

 varies continually, and it has the great 

 advantage that it is always deepest in bad 

 weather ; in onshore gales it is often 13ft. 

 deep. 



If Macquarie had a deep entrance, it 

 would be one of the finest harbours in 

 these colonies. Nature' does not always 

 make fine harbours where the}' are wanted; 

 she leaves it for men to make them for 

 themselves or go without, and where a 

 harbour is badly wanted, men generally 

 contrive to make one by some means or 

 other. If it had not been for the dis- 

 covery of the rich mineral country in 

 this part of Tasmania, Macquarie Harbour 

 might have been left to the swans and the 

 pelicans ; but the necessity for a deeper 

 entrance has now become sufficiently 

 urgent, and after suffering the pangs 

 of fear and doubt the colony has at last 

 made up its mind to take the work in 

 hand. There does not appear to have been 

 any grounds for doubt or anxiety as to the 

 result of the contemplated works, as the 

 effect has been pi^oved on dozens of 

 harbours which have carried out similar 

 works, and although the newspapers cited 

 as a warning some cases of dismal failure 

 of harbour w^orks in New Zealand, they 

 were not harbours of this kind at all, and 

 the success of them was at least doubtful 

 from the beginning. All those that have 

 failed ^xerQ enclosed harbours built off 

 an open beach, where the well-known 

 coastal drift was disregarded, which has 

 now overwhelmed one and gives serious 

 trouble in two others. 



Of course, if breakwaters are projected 

 out to sea from a beach which constantly 

 drifts in one direction, nothing can save 

 such a harbour from being silted up, unless 

 it has the motive power within itself to 

 keep its entrance clear, or unless it is kept 

 clear artificially by dredging or scouring. 

 Thus the harbours of Calais and Dunkirk, 

 where there is a constant drift of the 

 beaches from west to east, have their 

 entrances kept clear by sluicing the 

 channel from artificial sluicing basins, and 

 assisted by dredging ; whils the harbour 

 of Timaru, in New Zealand, is kept open 

 by a suction dredge. 



But harbours Avhich have the motive 

 power within themselves do not require 

 artificial assistance to keep their channels 

 open to the sea if their natural current is 

 controlled by suitable works, even 

 although they may have to contend with 

 the troublesome coastal drift ; thus the 

 harbours of Westport and Greymouth, 

 though exposed to the full violence of the 

 sea, and having besides to contend with 



the constant drift of the beaches towards 

 the north, and with vast quantities of sand 

 and shingle brought down by the rivers, 

 maintain their channel out to sea at a 

 regular depth of about 15ft. at L.W.S.T. or 

 24ft. at H.W., and have done so for the 

 last 10 years without apparent change. As 

 the tidal basins of these two harbours are 

 very small, the run of the tides in and out 

 twice everj^ day is not strong enough to 

 keep their channels clear, consequently 

 when floods in the rivers fail, the channels 

 gralually shoal up. But floods never fail 

 for very long, and the first flood in the 

 river restores the depth. 



Now, in the case of Macquarie Harbour 

 there is not onl}' an enormous tidal basin 

 of 72,000 acres, but the two rivers, Gordon 

 and King, have a larger water shed than 

 the BuUer River in Westport, with the 

 same rainfall of lOOin., and quite as 

 frequently flooded ; in addition to these 

 advantages there is no direct evidence of 

 general drift in the sea beach, and the 

 sand and debris of the rivers cannot reach 

 the entrance because it cannot cross the 

 deep water of the harbour, where, as I 

 said above, there is no current ; also it is 

 to be observed that in Greymouth and 

 Westport the rivers bring down shingle 

 up to some the size of a man's head, which 

 has to be swept out to sea to keep the 

 channel clear ; but the obstructions in the 

 entrance of Macquarie harbour consist of 

 the finest sand, so easily scoured that the 

 ebb current is able to maintain a channel 

 84ft. deep between Entrance Island and 

 the mainland, and 40ft. to 50ft. deep at 

 othei* parts liigher up. 



There is nothing new in the plans I 

 have submitted to effect the deepening 

 of Macquarie Bar ; it is the usual plan 

 adopted all over the world for situations 

 like this, the object sought being to con- 

 tract the current so as to get depth in 

 place of width, and in designing a work of 

 this kind one has to be very caieful so as to 

 strike a proper mean between undue width 

 and useless depth. In this case the width 

 is fixed at 1,200ft. between the two break- 

 waters, which are to contract the existing 

 width of about 7,600ft. Partly from ex- 

 perience, and partly from calculation, this 

 width of 1,200ft. is reckoned to give a 

 depth of about 25ft.; 1,200ft. by 25ft. is 

 somewhat less than the existing waterway 

 over the bar, but will really be a good deal 

 more, because the velocity of water flow- 

 ing through a channel is roughly as the 

 square root of the depth. 



While considering the depth one wishes 

 to get at the entrance, it is of importance 

 to avoid, if possible, throttling the tide in 

 the lagoon, because the more tide-water 

 that gets in and comes out again the more 

 eftective is the power to keep open a 

 channel to the sea. I know a lagoon of 

 about 9,000 acres which was provided with 



