146 Transactions.— Miscellaneous. 
that the town of Blenheim has been saved by this invention. Of all the 
money spent in conservation and attempts to divert the stream, these log- 
dams only remain, and when thrown up shingle can be retained, no danger 
need be feared for the future. It will thus be seen that the great problem 
of how to divert the current and make a bank of shingle where it can be’ 
utilised, has been solved in one of the most dangerous and rapid rivers in 
New Zealand. Unfortunately the conservation of rivers here is in the hands 
of a Board elected by the settlers from among themselves, and such bodies 
are not only slow to see, but timid in admitting the merits of a new idea. 
To make the matter clearer than can be done by written description I forward 
a small model of the invention. 
Art. XII.—On Beach Protection. By W. D. Caurszrr, Ass. Inst. C.E. 
Plate ITI. 
[Read before the Westland Institute, 15th July, 1878.) 
Tue encroachments of the sea on the sandy ridge upon which a portion of 
the town of Hokitika is built, have often been very considerable during 
tempestuous weather, and at times have created no unusual amount of 
alarm among the inhabitants of Revell Street. The subject of beach pro- 
tection will therefore be of interest and importance to many present, and I 
propose to briefly discuss it, prefacing my remarks by a glance at the 
conditions presented by waves in accumulating and removing beaches. 
The movements of shingle and sand along the coast are due to the 
waves, whose direction is determined by the prevailing wind, but tidal 
currents sometimes indirectly affect their action by subduing or increasing 
the waves according as they may be with or against their direction. The 
action of the waves may be taken to be of three kinds:*—1st. The 
accumulative action, which heaps up the particles against the shore. 
2nd. The destructive action, which breaks down the accumulations pre- 
viously made. 8rd. The progressive action, which carries forward the 
pebbles and sand in a horizontal direction. 
The difference between the first and second actions is determined by 
the rate of succession of the waves ; for when they break upon the shore so 
rapidly as to over-ride each other, a continuous downward under-current is 
produced and the destructive action commences. The progressive action 
takes place when the waves impinge obliquely upon the shore. 
* See “Observations on the ,Motions of Shingle Beaches,” by H. R. Palmer, C.E., 
F.R.S., Phil. Trans. Royal Society, 1834, Part I, 
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