HARBOUR SCHEME.

Timaru Herald, Volume CXXIII, 16 June 1926, Page 6

HARBOUR SCHEME.

DIFFERENT ASPECTS

“The scheme must be looked at in at least seven different aspects, or from ns many points of view, as at least six different questions are raised by the proposal, 1 ’ said Mr J. Hardcastlo; in conversation . with-' a representative of the “Herald” ■' yesterday afternoon. “The different aspects- 'are: (1) Engineering f of construction, regarding which there is no difficulty. (2) Enlargement of the harbour for the immediate purpose of providing an adequate ‘swinging arch’ for the safer handling of largo steamers When entering or leaving, a harbourmaster’s, shipmasters’, and owners’ point of view. (3) The range problem, chiefly the harbourmaster’s point of view. (4) The silting problem, as affecting the duty of dredging to maintain a deep channel through the shoaling area. ' (o) The probable effect on the Bay as a bathing and holiday resort; tho general public’s question. (6) The cost, . the ratepayers’ and the Prime Minister’s question. (7) The relation of the .work to the growing accumulation of shingle. Except the first, these questions 'ye* quire a good deal of consideration, severally or together. An off-hand expression of opinion about it would probably omit regard to some essential points. \ EFFECT ON THE BAY. 7 ' “Mr. G. S. Cray has dealt With; the effect on tlie Bay, as a pleasiii'e resort and from the aesthetic point of view, if Mr Clarke’s scheme is carried out,- 1 would add,” said Mr Hardcastle, “a little on what appear to be probable results on tho physical side. .if“lt is obvious that tho now north mole would not reduce the amount .of silt, sand and mud brought into •■;,the area of water sheltered by tho eastern mo’e. The new mole would, howeVer, reduce the area over which these materials would be deposited. More important than reduction of area, , at least for some years, is the new shape givon to that area adjacent to the Bay lawns. A 1 largo corner .is,shown on the plan, which tho waves in all probability will fill np with sand; whether gradually, so as to fi!l the area up;, to storm-reach level, or only partially/so-, ; r by. throwing' up a bar across the?outer part”'remains to be seen. If a bar’resulted there would be formed behind it a hollow in-which storm Water drainage from the land would stagnato until the hollow was filled up. If the filling of sand was complete, so large; an area of saiid would nave to be covered with vegetation somehow, or strong nor” westers would be able to drift much of it into the -pfeserlt' harbour and over the reclamation. ” “Tho engineers make muoli. of the ‘swirl round tho Bay,’ caused "by waves breaking on and southward of Dashing Rocks, tho tail end of the ;Swirl being an’iouttyard cui’i'ent albhg : tho north iViol.e. ‘ 7'' “If f the new mole' were constructed this swirl must be intensified in; tho ; inner end of the Bay, as it would have ; a: much'v reduced space in which to ) ; swing round, and a more rapid current j / must.flow along tho mole. The shorter swing round of the swirl, it seems to |.; me, would probably have an effect re l l l calling 'The Whip’ at Dunedin Exhibi- i tion, the sand being swept away froth . the west end of the beach to’the 'j eastern end, until tho curves of high and low water lines acquired quite new directions. The line of lamps along the i lawns scales (in straight; line) about 1 2400...f00t, tho high-water line about 1 tho same. ' Under the 'altered Condi* i tions the' length of beach would bo ; about 1600 feet, but longer tho further ] seaward : tho Hues ran, beyond the: foot of. the mole, “Apart from the problem of change in the sand deposit, it is more than i probable the compression of water i brought by waves into a, more sharply < narrowed - funnel-shaped bend of the 1 Bay during heavy sens outside, would : result in the level of tile water being raised move than it is now. The ; westorn lawn has been overflowed bv i tho waves occasionally. It is probable i that under tlie altered conditions this would'happen frequently, even to tho i flooding of tho tennis courts, unless an adequate’embankment be made to prevent it. i ’ “Mr Cray' suggested that the tri- i angle formed between the lawns and ; the new work would probably ho used as sites for warehouses. Tho Railway : Department might to some extent in- i tcrfcrc .with, or at all events modify, any sclicmo of that kind, in the in- i forests of the Hilcy idea of carrying 1 the railway across the Bay to Wai- i mataitai Valley, to avoid tho curves ; and steep grade on the town side of the Bay. That would mean tho end of ‘The Bay.*' 1 HARBOUR ENLARGEMENT. ‘ ‘The proposal to enlarge tlie harbour, in order to make the handling of steamers when entering or leaving more safe and easy, is worthy of favourable, considerat.on.. Such consideration must . not ignore feasible alternatives to oh- ' tain the samo effect. In conversation with tho harbourmaster, I learn that the spaco for turning a long steamer ■ is too small. A steamer lias to bo turned end-for-ond before going into, or after leaving a berth. The difficulty of turning a ship Is duq to tho move- 1 rneiit having to be made mainly by 1 means of the screw and rudder, and J it is a slow and tedious, process in the 1 ease- of ■ a-long- vessel. -In some, other 'j ports a tug is used to push a vessel J rouiidvby pressure ..upon, ,qr ~ hauling * ilpbUr one' end; Timarui cduld-not af- 3 ford a tug for such work, and there is ■ no other. work here fof . a tug-to do. A pull in the right direction on. one side rs as gobd as ’a pusli-o'n thoiotliev. ; ! A few electric capstans, suitablyhutuated, should enable tho harbour Staff to swing even tho longest steamer in her own length, and make unnecessary a vast outlay to attain the saffii}’ end. As for enlarging the harbour in- order to provide more wharfage accommodation at some distant future, Mr Cray has adequately dealt with this aspect of the proposal. • . , THE RANGE. - ‘.‘ln the ‘Timaru Herald’ of the 2nd inst. I wrote oil the range aspect of the scheme, stating, conclusions from a plotting of the courses of rangewaves due to seas from different directions. It appeal's .to .me that Mr. Clarke’s scheme provides for a great ; improvement as regards range at No. 1 wharf, but at the expense of Nos. 2 , and 3. I forgot.; to mention then < (though I had noted,lt) the prob- 1 ability that range 'Waves striking ■ squarely or nearly so near the end of the spur from the eastern mole,'.Would i be strongly deflected across the entrance, and probably .turned into It by i coa’escing with the part of the ware running in directly. The conditions for 1 this are not as bad ns in the ease of the 3 arm of tho north mole now, but they ( are of a kind to be avoided if possible. 1

DREDGING. “Mr Clarke’s scheme does not promise any reduction - iii the amount of dredging to be done after its completion, and his explanation dopt not refer to the vast amount to bo done before its Cbmplotion. He. says that the neiv north mole would ‘shoulder further a Way frbm the eh annul*' the current flowing from the Bar, so that ‘there may be less si ting in the channel from this source.’ There is, T .think, a tendency to attach too much importance to this current as a carrier end‘denositor of shoaling material. The Royal Commission of 1924, referring to this current in their reports, say that

it ‘carries a considerable quantity of j sand in suspension, which is deposited) off the entrance to the inner harbour, und between that point and the end of tlie Eastern Extension.’ The figures on tho published chart indicating soundings contradict this idea. Tlie 3 fathom lino (these words on tlie chart were smudged somehow) runs from the north molo straight away northward, and at right angles to the channel. Tho depths are greater near to it than they are further from it. Tliis proves that • the Bay current is not an important source of deposit off tho entrance to the harbour, of in the channel. (The'depths 20 r and. 23 feet marked in the angle of the channel and north, mole are duo to recent dredging there.) . “Another prevalent idea is that tho deposited materia! comes mainly from tlie south round the end of tho eastern molo. Tho i soundings lines appear to contradict-this, as they have swung 1 outwards faster on the west than on ‘the east sido of the Bay. The outward movement of the high and low-water lines of the sands have not done so, but the saind is moved eastward by an along-shore current. (part of the swirl round tho Bay). It would be interesting ;to' know lioW far from the Iqwwater line of the sand is the. dividing line between sand, and the mixture of sand, silt and mild which is tho shoaling material over the greater, part of the Bay. Seeing that the" 1 fathom lino hits moved outward at a much dividing line may be near that line, slower rate than tho deeper lines, tho , “It is'father surprising that a trench 25 feet deep can bo maintained .at all through a bed of mud and silt without constant or frequent dredging along its whole length. The explanation of this must be due to tho fact, stated by Messrs Holmes in their report, that ‘the deposit is practically cemented together by the mud, which has, a high cementitous value,’ and which ‘renders tho. material very , refractory to dredge.’ It would -seem that the material, if allowed time to become well set, requires a heavy sea to disturb it, and heavy seas are cut off or much reduced by tho eastern mole, as regards much of tho length of tho channel. The depths marked on each side' of the channel nro greater than those opposite to them, further away. This is probably duo to tho drifting into the channel down its sloping sides, of newly arrived of arriving material.' The Royal Commission’ in their report said: ‘Deposits of sand atld silt appear to have accumulated, during the last fourteen'years nt the, following rates'per arihum:—ln Caroline Bay 96,500 tons, in : the dredged channel 68,000 tons, In the area between the dredged channel and tho eastern mole 51,000 tons; . total 216,000 tons per niinum.’ In the channel, then, more than one-fourth, nearly one-third of the to.tal deposit was made, though its area is but a small fraction of the. total area of deposit, and the channel and the area between it and the eastern mole, receive more than onehalf of the total. This Is incredible. There must .have been some error in tlioir data,, or in the use made of them. “Under Mr Clarke’s proposal tho length of dredged channel outsido tho harbour would be reduced bv 800 foot, leaving about 1600 feet. But this is to be, deepened by two or three-feet, whiqh means dredging in solid old land the whole way. With a deeper dinmielitliei-D must bo ;! a .grteater ten-dency-for the drifting in of material ■from caoh sido, therefore there would bo no diminution of maintenance dredg- , ing. • Then there is tho enormous amount of dredging.required to eniargo the. harbour, evoli if-only a ‘swinging basin 1300 ft in diameter’ were dredged. The average depth of material to bo shifted would be about 15 feet, 'tho lower half of it in hard Old New Zealand, COST OF THE SCHEME. “Mr Clarke’s explanation of his scheme includes certain estimates, totalling £190,000.. The items given I do not cover the whole of tho ground The public as well as a Royal Commission (and the Prime Minister) will have to bo satisfied that no material item of expenditure is omitted from the calculation. Tho cost of stono from qiiarry is probably pear tho mark, but is 11s per ton enough to allow for lifting the outer and. heavier part of the north mole? Nothing is set down for special plant for this, work. Surely tho_ little Taniwha is ; not expected to ao it, at that rate? It is not as if this job could be deferred. The Rcliome hinges , upon it-.being done, as tho now north mole. could not be completed as drawn until at least a part of the piesont molo is mover],-. The entrv and of , vessels would bo too 'risky, J hen there is nothing put down for RJ'eafc amount of dredging contemplated. No word of a. second dredge to get the work done) and the enlargement made useful, as far as a swinging basin is concerned!” °