THE UPPER HARBOR IMPROVEMENT SCHEME.

Evening Star, Issue 3978, 24 November 1875, Page 2

THE UPPER HARBOR IMPROVEMENT SCHEME.

With the view of enabling our readers to understand what it is the Harbor Board have decided to bring Major Gordon from Melbourne to report upon, we propose to cive a short sketch of the scheme of haibor improvement which the Hoard’s Engineer (.Ur D. L. Simpson) now asks that body te [definitely accept and to proceed with to a conclusion. From Kilgour’s Point, the termination of deep water, and the junction of the north and south channels to about half-a-mile‘ on the Dunedin side of Burke’s Brewery, there is a depth at low water varying from twelve to eigdteeu feet. From the last-mentioned point to town the water shallows from four to seven feet, while ; in some places here there is as little as three feet at low water. The dredging operations that will have to be undertaken to obtain the_ deep water channel, which is the main aim of the scheme, will com ■ commence at Kilgour’s Point, but the j difficulties of the work do not begin there. I Except opposite Arden Bay, where the water j shallows to nine feet, and in some parts to ?. j little less, there is vight up to Buike’s au aver | age depth at low water of 15ft. AU this dis-

■ tance the channel bed admits of easy dredging, i For perhaps half a mile above Bmke’s there , is plenty of water, averaging fourteen feet, but 1 the moment the edge of the large sandbanks, ! which are exposed at low-water, is reached it shallows to between two and three feet at low , water. These banks are three in number, and it is upon them that a great d-al of time and , attention will have to be bestowed By going ! more inshorewar Is, Mr Simpson coaid 1 have obtained greater depth of water at this point, but. he gains that further on, and secures something like uniformity of design for the channel he proposes to cat The scheme proper provides for a channel 100 yards wide, but the Harbor Board are inclined to adopt the suggestion thrown out by Mr Simpson that a channel 100 feet wide may answer t he requirements of Dunedin for many years t« come. On this point Mr Simpson himself says—

The time over which these improvements are estimated to extend is 9} years, but this is for the completion of the entire works, which will provide accommodation suited to all future requirenn uts. The temporary work of deepening to a less width, say fcrd = 100 feet can be effected, of course, in a proportionately shorter time.

This channel will extend from Kilgour’s Point to the head of the Upp- r Harbor, and be dredged so as to maintain an average depth at low Witer of eighteen t'eet as far as the red beacon, at the end of the present training wall. The channel will be protected by a half tide training wall, to be built of rubble, which will run para'lel with it till opposite Peiichet Bay jetty, when it will take an outward curve and terminate at a point midway between Kattray street and Vauxhall jetties. The object of this wall is thus explained by the Engineer:— Interference with ordinary tidal action is not contemplated in so far as regards the main work of channel deepening, inasmuch as by the erection of the half-tide wall on the position indicated, extending from Kilgour’s Point to Dunedin, it is only intended to couliue the stream within n limit sufficient to control its direction up to the period of its maximum velocity, which experience has proved to be as near os possible at half duration in each case of flood and ebb tides. The wall is placed at a distance from the beach adequate for providing a width of tidal capacity as far as practicable, from the configuration of the bench, uniform in section. The necessity of carrying the wall along the full extent of the sandbanks will be apparent when it is explained, that the action of Hie ebb tide, when slightly above the level of the banks, is in a direction transversely to the stream, and it has a force sufficiently strong to move the particles of sand to within the confines of the current.

Between Arden and Blanket Bays a second half-tide wall is to be constructed, the object to be obtained by this wall being the closing up of two distinct channels at present in existence, and the concentrating of the current in one channel, and so utilise its full scouring power. On this subject the engineer reports :

Between Blanket and Arden Bays and the main sund bank opposite four distinct channels exist, immediately above Kilgour’s Point. The divisions of the current at this part have no doubt been caused by the projecting headland, and as a result the scouring effect upon the bed has not been sufficient, if at all effective, in maintaining the uniform level of that part of the main channel immediately above where the currents again become concentrated in the on* stream.

Now a word or two as to dockage and reclamation. The total area to be reclaimed is set down at 422 acres. Ihe filling in of I’oliche'

' ’.ay will give 73 acres ; of the foreshore b - wee i die Bo.id's endowment and high water mark (not including the aiea bounded by (dasthi reef, ftii'.rl street, th endow meat and the ructions lately sold by the Government) 19 acres; of the area between Albany street and

the new channel o! the Water of Leith, 20 acres; of sites for warehouses, itc., 279 c, j 8 V a f° r -streets round the docks oid between the si earner basin and Anersons Bay 32 acres. It will be ob--erved that reference is made to a new channel •or the Water of Leith, which will then dischfvive *i_a point about half a mile below • -oglu's Point. The made banks of the stream vill be pitched and rendered secure against floods ; and it is evident that during floods any debris likely to accumulate will be carried down to within the confines of the coastal current. The front line of reclama. ion is to be carried to <he limit assigned m the Crown giant to the Superintendent. T.tis limit tna\ lu* *Jo"ori.)icl Jas «xtending seaward ahou*- 35') yards from the head of Stuart street wharf, tnk.ng .hat as« central point, and he limit of reelmation as from the Anderson’s Hay road about 530 yards also seawards. The docks will be four in number. The first is the export dock, which will havs an area of fifteen icres, furnishing a berthage of 3.08?* feet, aud to b# dredged to a depth of 22 feet at low water. Between the Pelichet Hay end of the reclama* non and the export dock there will be an area of 32 acr-s available for building leases. Iht second, or tidal import dock wnl be of imllar iim. nsions, and have similar herbage and depth of water in it to ■ lock .No. I. On all ihe land bounding these two docks it is intended to erect bonded warehouses, he i'rinpinal access w ich will bo from Stua>t street. The whole of the area between attav -tree! w an and the i idal import d'ck -some hi teen acre* in all—isj to be re-

laimed, and wi i he available for building leases. The bird dock, situated between Jetty and Ka l tra> streets, is for intercolonial ami inWprovuic-al Bt--amer«. it will have an area of 274 acres give berthage of 4,380 lineal feet, and possess an average depth of 174 ft t Beta tliis and the last dock for coal and timber ves els, there wi l l be an additional ten acres avai aide for building purposes. The coal and timber dock have an area of nearly 234 acres, a berthage of 4.200 lineal feet, and a depth of 14ft at low water. This dock will be hounded by land for coal and timber yards, hav ng an area of 27 acres. It should beiememhered that fr in the red beacon the main channel will gradually shallow from eighteen feet at the entrance to the tidal import dock to fifteen feet at tin. steamer dock, to twelve feet at the co -l dock, and to six feet opposite the ship's budding yards, for which aud non yard a total ar a ot 130 acres will be provided m part of -he Anderson’s Bay road, .1 ,. |p a * , ea4.U acres will be occupied by shipbuilding yards, which will front the six-feet channel. At the term,nation of the 6ft chan--1 nel will be a log basin. ; In the construction of the main channel to its i original width of 300 ft, Mr Simpson estimates ; that nearly 5.000,000 cubic yards of stuff will be dredged. If the width of the channel is re--1 duced by a third, the quanf.it ■ so £0 be dredged t will be about a million and a-half cubic yards, - which lias to he added the stuff taken

from the other channels, docks, and basins, estimated at 3/202.009 cubic yards The hulk of this stuff will be use lin reclamation; the rest it is intended to deposit in Blanket and Arden Bays up to the b-vel of low water. 1 he cost ol its remov ti uhJ deposit is set down at wi per ya.;«i. J • the wdls are estimated to cost L 22.4 0' ; ti e tiiin-g m behind the timber wharves and ab-ng the foil extent of sea hue of reclamation, 1.69,000; and the timber whaves, which flouting the export . lni P°rt docks will have a width of 30ft, and butw en tne other docks and basins a width of ?oft, L 226,000 ; u j redg ' ng wi ‘ l tlie “ Kra ” and inn r « dge ,low e * n K buil* at a cost of nearly L 20.000 by Messrs Kincaid, M Queen, and Co., three screw barges, capable of carrying trucks containing 100 cubic yards of stufi, at an average speed of six miles an hour ; while for the purpose of reclamation, the haulage is to be done by locomotive power. The daily working expense of dredging and reclamation is set down at L4O. In reclaiming IMichet Bay and toe various sites already euumerated, over five mdhon cubic yards of material will be absorbed ; and to accomplished this, and to give a channel to Dunedin of eig l tevn feet at low water and 100 yards wide, will take about ten years ; and its cost, with the concomitant works, will be JL611,000.