H.—] sa.

above-named engineers have been begun and are being carried out with vigour, and their final success is now certain. It has been found that by carrying out a mole to an obtuse angle to the set of the waves of the prevailing seas that the waves will run along the wall and will be reflected along the beach, and that when the mole is sufficiently far out that the force of the reflected waves or backwash will be great enough to drive the shingle back from the works. The shingle will then deposit along the beach behind the works instead of advancing to overwhelm them, and will in time form a valuable reclamation." Mr. Goodall had already tested this theory at Timaru, and claimed that it had been a success there, where the problems to be met bore a close resemblance to those at Napier. His suggested scheme was adopted, and it was at his advice and to his designs that the breakwater was built. The angle at which the breakwater was thrown out from the Bluff was carefully planned so that it would meet the prevalent seas in such a way as to procure from them the maximum amount of power, in the form of backwash or reflected waves, to drive the shingle back. It may be said that the events since the breakwater was built have thoroughly justified Mr. Goodall's foresight and theory. Other engineers reporting on the work since that date have agreed that the angle at which the breakwater is thrown out is well chosen, and it may be taken as a proved fact that so far, after a test of over forty years, the breakwater has apparently stopped the flow of shingle at the point. In 1925, in Messrs. Cullen and Keele's report, a further theory is advanced as to the effect of the breakwater, and they say : — " The breakwater has been carried out at an obtuse angle to the set of the prevalent seas ; it now forms a complete bar to the further travel of the shingle to the north. The waves strike the wall with great force, and, running along it, are reflected towards the beach. An accumulation of the water from a succession of reflected waves causes it to head up in the bight to the seawards of the commencement of the breakwater, and a strong backwash and undertow is created which, running along a well-defined channel leading around the north face of the rock shoal, as shown by the contour-lines, draws down the shingle, which is again thrown back against the breakwater by the next incoming wave, the result being that the shingle is finally reduced by attrition to mud, which no doubt is carried away in suspension by an undercurrent which is generated in all bights and indentations along the coast, and running radially from the shore seawards, and is responsible for the main contour at those places." Here we see two ideas put forward : the first is that the action of the seas which are diverted and thrown back by the breakwater is not only to check the northward drift of the shingle, but to create a veritable grinding-mill which grinds the shingle up into mud ; secondly, there is the theory that this mud is carried away in suspension by an undercurrent. The first of said theories—namely, that the breakwater converted the action of the strong seas into a shingle-grinding mill —is generally accepted, and from the appearance of the shingle at the bottom of the breakwater it may be taken as proved. The theory that the mud created by the final disintegration of the shingle is carried away to the sea was also put forward in the evidence before us by Messrs. R. W. and J. D. Holmes, and is a matter that must be considered at a later stage of this report. Sand-drift. The theory is also put forward that there is a drift northward of sand, not at first where it can be seen, but at some distance out where it cannot be seen. Messrs. Maxwell, Williams, and Mason in their report of 1909 say : — " Since the construction of breakwater large accumulations of shingle have taken place along the beach in front of the town and the Blufl, and during heavy southerly weather it accumulates in the corner at the root of the breakwater and is driven over the wall there. There is no trace of shingle beyond the first cant of the breakwater, and indications are that nothing but fine sand is carried past the work, although it is probable that the accumulation south of the breakwater has not yet reached its limit, and that when it does the quantity passing will be larger than at present. This drift of sand around the breakwater, but for the opposition of the ebb currents from the Inner Harbour, would spread out towards the Petane beach. It now, no doubt, assists in forming the bar which is found about 3,000 ft. outside the moles at the entrance to the Inner Harbour, and on which the sea breaks during heavy weather. This has always existed to a certain extent, but has become more pronounced since the construction of the breakwater; the ebb tide, owing to the stoppage of the shingle drift, being now able to prevent its being spread out towards the beach, while the accumulations in the neighbourhood of the entrance have entirely disappeared owing to the stoppage of the supply of shingle. We examined the bottom by dredging with the Board's grab-dredge "J. D. 0." from this bank inwards, and found the bottom is composed of sa.nd from about 2,000 ft. from the end oi the eastern mole ; thence inwards it is composed of shingle, increasing in size as we approach the entrance. . . . This sand-bar and sand-drift are, in our opinion, the critical features in connection with the proposal to establish an Inner Harbour suitable for the largest vessels." In giving evidence before the Commission Mr. J. P. Maxwell again referred to this question. He said that he could see no other way of accounting for the large amount of material other than shingle which comes out of the rivers south of Napier, and he rejected the suggestion that they were carried out to sea, but maintained that they must be carried northwards in the ocean current. He referred, secondly, to the evidence afforded at Timaru by the presence of a belt of discoloured water parallel with and perhaps one-half mile out from the shore, but admitted that he had not seen the same phenomenon at Napier. He said that evidence of " making "on the Petane Beach as deposed by Mr. Furkert could be accepted as further evidence of the existence of the sand-drift.

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