D.—No. sb,

When the Taieri is in flood, much of the silt which it holds in suspension is deposited in the overflowed plains which are thus being gradually warped up (and at I think a higher rate than the bed at Outram can be rising). This effect is increased by the diggings; but if it were not for the beneficial influence of the Taieri Lake, or if extensive diggings were opened below the lake, there would be great risk of sand being spread over tho plains instead of silt —of course to their destruction as farming land. The inquiries which I made of settlers living on the banks of the river, tend to show that no perceptible rising of the bed has taken place. They all agree that although, when the river is low, fine silt is deposited, it is at once removed when the river rises. As far as I could ascertain, the fords of the river are not materially changed. It is, of course, very difficult or even impossible for any one to know, without levelled cross sections, whether any rise in the bed of a river is taking place ; and even with them, unless they were very numerous, it would not be much better. The course of the river is never quite the same for two years running, and the deposit of a bank at any known spot would naturally lead to the opinion that the river was silting up, although at other points it would be deepening, but, being out of sight, would escape notice. In conclusion, I am of opinion—Ist, That the bed of the Taieri is rising at and above Outram, but slowly, and that for tho rest of its course the level of the bed is quite permanent. 2nd, That although there is a possibility of the river taking a new course from Outram to the Lake Waipori, it would probably not injure the Clutha Railway by doing so, and is altogether too remote a contingency to make it desirable to incur any extra expense in laying out the railway in order to meet it. I have, &c, The Hon. the Minister for Public Works, John Caeetjthees. Wellington. Engineer-in-Chief.

III.—TIMARU HARBOUR WORKS. Mr. Caeeutiiees to tho Chaieman, Timaru and Gladstone Board of Works. Sir,— Timaru, 29th October, 1871. I have the honor, in accordance with instructions, to submit the following report on the Roadstead of Timaru. In November, 1805, and in September, 186S, the late Mr. Balfour wrote two valuable reports on the same subject; these, together with his plan of the roadstead and a very elaborate survey made by Lieutenant Woolcombe, have been placed at my disposal, so that I have had considerable facilities for acquiring information. I have also examined the beach for some miles on each side of the town, and have gathered by personal inquiry of persons acquainted with the roadstead such information as could be procured. Above all, I have carefully observed the experimental breakwater constructed by Mr. Balfour. It is agreed by every one acquainted with the subject, that the prevailing seas come from the South-east, and this is fully corroborated by the trend of the coast at points where the beach does not seem to travel. The trend of the coast between the Waitaki and Timaru and for some miles to the North is some, what East of North, so that the seas break on the beach, not at right angles, but obliquely, at an angle of about 50 degrees. It is to this obliquity that the motion of the shingle is due which makes Timaru •so difficult a port to improve. When a wave coining from the South-east breaks on the beach, it carries the shingle forward with it in a North-west direction ; the retreating wave does not, however, travel back on the samo path, but runs down the slope of quickest descent, which is at right angles to the beach, or nearly East. Each piece of shingle, therefore, trails northwards in a series of zig-zags. It is evident, since the motion of the shingle is due entirely to tho breaking of the waves on the shore, that any work, such as a breakwater, which would make still water on the beach, would deprive the shingle of all northward motion. It is not necessary that the breakwater should be attached to the shore : still water is as effectual a barrier as a masonry wall. The shingle being thus stopped, it would collect on the south side of the breakwater, until iu tho course of time it had pushed out to the end of the latter, when the northerly motion would begin again. In the meantime the shingle to the north, beyond the protecting influence of the breakwater, would have been still moving northwards. As no new shingle could come to supply the place of that which had moved on, the coast would soon be bare, and the sea would begin to cut down the sub-beach. These remarks apply as well to an imperfect as to a perfect breakwater. In the former the effects would be slower to show themselves, as, owing to the imperfect stoppage of the waves, a part of the shingle would continue to move along the beach, but the final effect would be the same. The practical question to be solved is, at what rate does the shingle travel ? Mr. Balfour found that some blocks of wood loaded with lead, which he threw into the beach, travelled as much as a mile in a day, even in fine weather. This would indicate a very rapid rate of travel. The experimental breakwater consisted of a concrete wall thirty yards long, placed on a reef below low water, and detached from the shore. It was hoped that the shingle would continue to travel along the beach, as the landward end of the breakwater was further to seaward than the line to which the shingle was drawn back by the undertow of the receding waves, and the breakwater was also so small that it was not expected to offer any perceptible protection from the beat of the waves on the shore during rough weather. It was found, however, that the protection given by this small work was sufficient to prevent the shingle from passing across the stiller water behind it. It was heaped up between the breakwater and tho shore, and then behind the breakwater. To leeward the shingle was all carried on to the North, and tho sub-beach cut away sufficiently to endanger the large store at the landing-place. This effect was perceptible at the foot of Caroline Bay, half a mile from the break-

6

REPORTS OF THE ENGINEER-IN-CHIEF.