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The Pamphlet Collection of Sir Robert Stout: Volume 26

Suggestions as to Works

Suggestions as to Works.

I shall now proceed to offer some suggestions as to alterations on former schemes, and the substitution of now ones. In doing so, I would remind the Committee that I have at the outset reserved the right of modifying them, should the information on which they are based be incorrect or incomplete.

With reference to the central training wall proposed by Mr. Balfour. Before proceeding to construct it, I would be inclined to make some experiments to determine whether any benefit would result from the erection of certain portions of it, or if the remainder could not be altogether dispensed with. The most important of those experiments would be one at the point where the channel divides into two. It is quite evident that the principal if not the only cause of this division is the existence of a very prominent headland between Sawyer and Blanket Bays, together with a shoal or rock immediately opposite, directly in the centre of the channel. If the latter is composed of hard material, that alone would split the current, and deflect it into the present courses. Now, if the obstruction in mid-channel is removed, and a groyne thrown out on the north-east corner of the lower bank, it is possible that the greater portion of the tide now flowing into the south channel may be diverted into the north one. If so, the scour would be greatly increased, and in all probability the channel deepened. The cost of making the experiment would be comparatively trifling, and as the chances are that it would be beneficial, it is well worth trying.

Another experiment is the construction of that portion of the training wall between Bull Island and Black Jack's Point. By referring to the chart, it will be observed that the two channels rejoin about the former place—or rather, that they cease altogether there—for above it the Harbour is a uniform depth right across. The erection of this portion of the training wall might be the means of confining the water and increasing the scour, and extending the channel towards Dunedin. It is also possible that the scour would be further increased by producing the wall to the line of Vauxhall Jetty, and doubling it back in a pear shape.

Another idea has occurred to me with reference to increasing the scour. It is, to make the railway embankment across Pelichet Bay watertight, and to run another of the same kind from about Jetty Street to Burns's Point on the Peninsula, and to use the area thus enclosed for holding the tide till near low water, when it would be allowed to escape into the channel. This method of scouring is extensively used in tidal basins throughout Europe. I believe that the effect from the two reservoirs above named would be perceptible for at least two miles down the Harbour. Of course, the embankment across to the Peninsula could be utilised as a road or railway.