THE HARBOR.

Gisborne Times, Volume XXII, Issue 1733, 26 April 1906, Page 3

THE HARBOR.

MB LESLIE REYNOLDS’ REPORT

The following -is the report from Mr Laslie Reynolds, C.E., upon the Gisborne harbor :

Wellington, 18th April, 1906. The Chairman and members of the Gis borne Harbor Board, Gisborne.

GsntlemeD, —Acting under your Board's instructions, oommunicated to me on the 30th January, I visited Gisborne, and between the 4'h and 18th of February, devoted my time to examining the harbor, and investigating, the conditions which would be likely to affect any conclusions which I might come to in reporting to your Board. I also, with your Beard’s concurrence, instructed Mr George Grant, of Gisborne, to procure further data relating to to the depths of water over the different portions of the harbor, and to the nature of the bottom. This informatun, which has beou well obtained and oarefully plotted, reached mo on the Id h uit., and from the plans sent me, a copy of which I understand was forwarded by Mr Graat to your Board, I have reduced to accompanyiog plans upon which are outlined the works which I would reoommeni w't’o a 7iew to further improvement of the harbor. Before proceeding, it might bp well to osplain, although I believe Mr Grant has already done so, that a differonoe of Ift 6’n exists in the zeros of the two tide gauges ; that on the tewn wharf, which I understand was fixed during the Admiralty Survey by the officers of the H.M.S. Penguin being lft 6ln lower than the gauge on fcho breakwator. Mr Grant, how ver, adopted the levol of low water at sin below the zero of tbo breakwater gauge, and for the purporo of this report I have accepted such as low water datum, hut should the Admiralty da.um be regarded as correoi, the soundings sbovtn upon Mr GraDt’sp'an should be reduced by lft lin Upon referring to tho old charts and plans, prepared prior to tho construction of the breakwater and the western wall, it appears that the depth on the bar and along tbe lino of fairway was generally from 3ft to 4ft at low water spring tides, whereas new over tbe same distance the limiting dr pi h is about Sit 6:n. Such imp.ov mint, in view of tho comparatively ema 1 volume of water which passes into and out from ll o liver snd eituiry is very satisfactory. Doubtles', owiDg to this improvement, it might by some be considered practicable to further increase thiß depth considerably, but in my opinion the present depths nearly maik the limit of natural improvement, that is to say, th’f with the normal outflow of river and tidel waters comtined, which I approx'mate at s >me 35 000,000 cubic feet per tide, it is not possible to obtain much more ssourieg depth without reoourse to a sluicing basin, by wbioh the valooity of discharge during periods of ou flow could be considerably Higmooted. Although the Waimata river during normal discharge of Bay 15,000 oubie feet per minute, cannot be considered a silt-bearing river, there oan be little question that during heavy freshes it

c n'ries ft considerable quantity of sllt> whiob, wero not tho present depths in tho bar- . tor very materially improved by dredging, would 80ttlo and roduco auoh dopths to [ that which tho rivor would maintain dur* ing normal conditions. It therefore follows that if any material iuoroneo is to bo ob» tainod and maintained, without oors do> able and constant dredging, artificially ico.'oasod scour mint bo forthcoming. Tho only menus by which this oan bo accomplished is by utilising the Taruboru and Waimata rivors, whioh havo a capacity of seme thirty millions of oublo foot portide, os n sluioing basin, by oonstruoting eluioo gates indicated upon tho accompanying plan immediately bt low the junotion cf those two streams. Properly arranged I sluioo gates would allow the inoomiog tide froO'Bcooss to tho upper roaohos of these rivors, but on tho ohongo of tho tide the gates would oloso and rotain tho water above them, until a period approaohiog low tide, when it would bo liberated over a period of say two hours in volume equal to some 200,000 oubio foot per minute, which is more than doublo tho normal tidal and rivor disoharge during spring tides, and approximately equal to tho rate of flow duo to a fresh of nearly liin. raim fall in 24 hours on the oatohmenl area ol Turanganui rivor, The plan herewith outlines further wharfage aooommodation, whioh I consider most suitable to tho physical conditions affecting the case. Upon referenoe to the plan, it will be seen that 1 oonolude that further wharfage should extend from tho bridge down stream, and parallel to tho present wharf, for a length of somo 800 fee*, tbenoe in a direction to meet the top end of the Kaiti wharf. The width between the present berthages of the town side and the above suggested wharf would be 250 feet, as with any material inorease on this width the depth | would not bo efficiently maintained by soour. The area shoreward of this proposed line of wharf would be reolaimed by the dredge soil. It has been suggested, I believe, to reserve this area for a future floating basin, but suoh suggestion, owing to the oost of resuming the laud to obtain suffioient area, and of constructing suoh basin, in my opinion eliminates it from consideration. Should a floating basin ever be required, I would suggest that it be constructed at the mouth of the Waikanae lagoon, approximately where outlined upon the plan, ‘ and where direct communication with the railway could ba obtained. Assuming that the sluicing basin referred to be constructed, together with proposed lino of wharves, I estimate tha) a depth of 15 feet at low water could be ma'ntained t

tba berthages, and the depth throughout the fairway at 12 feet L.W.S.T. The dredging necessary to obtain the above depths, allowing that in the fairway from the beitbage seawards, the width of out be 150 feet, amounts to 205,000 oubio yards, of which I estimate 95,000 oubio yards will be mud and stiff clay, and the balance p obably papa. After considering the question of dredg* ing with regard to the most eoonomioal acd expeditious method of working, I have deoided to reoommend your Board to adapt the present dredge so that it could perform the work by means of a centrifugal pump, and discharge the spoil ashore through pipes. In connection with this I have oonsidred the question of obtaining a gold dredge of the buoket ladder type, eeeond-band, from which the spoil oould be dumped into a barge, and thence pumped ashore by centrifugal pump, but 1 have concluded that it would be more satisfactory to adapt the present dredge, as above explained, as wfth slight altera* tion to the bull it oould be transformed nto a very serviceable suction dredge, which would readily deal with the silt aad st-fl

olay, and even the softer seams of papa. There are seams of papa extending throughout the harbor whioh it would be pract : cally impossible to dredge without reoourse to blastiog, but as far as my investigations go I am satisfied that by far the larger portion oan be readily excavated by a suction dredge if such be properly equipped with cutting machinery on the mouth of the suction pipe. I therefore propose that to the present dredge there be added a suction pipe with cutting maohinery, driven by an engine of 20 i.h.p., and a 12in centrifugal pump, obtaining its power from either a steam engine oon-

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