Works, having for their object the protection of the sea-beach, should divide the destructive and progressive actions of the waves. This requirement 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. B. Pickwell, A.I.C.E. With main piles 27 feet long, and sheet piles 15 feet long, the rate per yard run would be 15 lin. feet main piles, 3 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 300 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

thick. At Cranz, on the Baltic, rows of piles 8 × 8 inches and 10 to 12 feet long, spaced 13 inches apart, have been successful, with a breastwork of piles and fascines. Breastworks are often required in cases of low foreshore or where a cliff is exposed to rapid erosion by the sea.

[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]

Beaches have also been successfully formed along the sea barriers of reclamation works by means of groynes. At Sunderland, successive additions were made to the reclaimed area as the beach formed. In 1874-5 the author had charge of similar works at Ayr; a reclamation of 24 acres of foreshore for a dock was made, and six groynes with stone filling, each 150 feet in length and 250 feet apart (see figs. 3 and 4), were constructed along the line of sea barrier in order to collect a beach in front of it. In the first year after their erection a rise of two to three feet took place. With main piles, having a nett length of 31 lin. feet, the rate per yard run with scrub and stone filling, instead of wholly stone as shown in the drawing, would be 18 6/10; lin. feet main piles, 2 ¾ CBM timber in way-balks, walings, cross-ties, and planking, and 50 lbs. iron work in bolts, 3 ¾ lbs. spikes and 21 lbs. in shoes; scrub and stone filling 17 ⅓ cubic yards. The cost of 6 groynes, each 66 lin. yards, would be about £5,300.

On spits and low beaches exposed to encroachment, groynes require to be constructed first, and then rows of fascines and scrub can be placed with advantage along the crest of the beach. The scrub placed along the beach at Hokitika probably assisted the accumulation of sand behind it; but without groynes it cannot affect the action of the sea at the foot of the beach where the erosion is greatest, and encroachment proceeds until the scrub is undermined. The rough cribwork groynes that Mr. Rochfort placed on the beach in 1867 and 1868^* were efforts in the right direction, but a much greater length would be required for efficient protection. The formation of a broad beach upon which the waves can expend their force is of far greater importance than a high narrow ridge which must always be liable to be washed down by heavy seas.

The fetch or reach of open sea is considerably greater here than at those places that I have mentioned, and the waves from that cause must be larger; but the depth of water off Hokitika at ½ mile and 1 mile distance is 26 and 42 feet, at Sunderland it is 27 and 52 feet; while the range of spring tides at Hokitika is 9 feet, and at Sunderland it is 14 feet 6 inches; and it must follow that the power of the waves are more broken here, having to pass over shallower water. I believe the design shown in figs. 1 and 2 would be efficacious, and it has the merit of presenting the minimum amount of surface to the seas.