CaupBELL.— On Beach Protection, 147 
Works, having for their object the protection of the sea-beach, should 
divide the destructive and progressive actions of the waves. This require- 
ment is fulfilled by piled and planked groynes, constructed at right angles 
to the shore line, their tendency being to collect and retain the sand and 
shingle. When the waves approach the shore exactly at right angles, the 
groynes will have their minimum effect, as no progressive action exists, 
The constant shifting of the beach, however, at Hokitika, either to the north 
or south, shows that an oblique direction usually prevails. Groynes have 
been found to be most successful in similar cases of encroachment on the 
coasts of Great Britain. In the Baltic, a double row of piles has been found 
to succeed; while on the Dutch coast groynes are constructed of fascines, 
where the dykes are more than usually exposed to the waves. The English 
practice is to drive the piles from one-half to two-thirds of their length in 
the sand or shingle, either in pairs, placing planking between them, or to 
have a pile on alternate sides of the planking. Sheet-piling would be 
particularly advantageous, and is shown in figs. 1 and 2, which “closely 
resembles a design by Mr. R. Pickwell, A.I.C.E. With main piles 27 feet 
long, and sheet piles 15 feet long, the rate per yard run would be 16 lin, 
feet main piles, 8 CBM timber in planking, sheet piles, and waling, 51lbs. 
ironwork in bolts and 30lbs. in shoes. With planking only, the quantity per 
yard run would be 15 lin. feet main piles, 1 CBM timber in planking and 
40lbs. ironwork in bolts and 8lbs. in shoes. 
To protect the beach from opposite Camp Street to Hampden Street, a 
distance of 770 yards, six groynes, each 66 lin. yards in length, might be 
placed every 154 yards. Their cost would be about £3,000. With the 
foreshore thus protected a line of scrub and saplings could be placed with 
advantage along the beach. The cost would be about £500. 
As instances of the successful conservation of foreshores by groynes, it 
may be mentioned that, at Spurn Point in Yorkshire,* piled and planked 
groynes were used by Sir John Coode, and in four years the line of bent 
grass had extended 200 feet to seaward, covering many drift banks; also at 
Withernsea,+ in the same neighbourhood, some groynes 800 to 350 feet 
long were constructed 200 yards apart by Mr. Pickwell; the piles at first 
stood ten feet above the beach at the land end and six feet at the sea end, 
the upper five planks were added as the beach accumulated, and in four 
years the groynes were nearly covered; at Eastbourne and Folkestone 
groynes of similar construction have been successfully used; at the former 
place they were constructed 150 yards apart, the piles were driven in pairs 
with two walings and a centre row of closely driven sheet-piles six inches 
* Proc. Inst. C.E., Vol. XXVIIL., p. 503. 
1 Proc. Inst. C.E., Vol. LL, p. 206. 
