THE HARBOUR

Wanganui Chronicle, Volume 72, Issue 173, 23 July 1929, Page 8

THE HARBOUR

TWO ENGINEERS REPORT CHAIRMAN S PROPOSALS REVIEWED When the matter of improving the Wanganui Harbour was reported upon by Mr G. A. Lee, consulting engineer, to the Board, and proposals on the same subject were submitted by the chairman (Mr J. T. Hogan), it was resolved by the Board that the latter be submitted to Mr Lee and Mr H. V. M. Haszard (resident engineer) for their opinions thereon. At yesterday’s meeting the two engineers reported their findings as follows: — Mr G. A. Lee’s Opinions. I am in receipt of yours of the 4th inst. enclosing a copy of the chairman’s proposals submitted to the Board and adopted at its last meeting, also your instructions that the Board would appreciate my views upon the tame. The scheme adopted embraces the raising and extension of the moles being the main works recommended in my report. The Board’s policy to energetically prosecute works calculated to give deeper water at the harbour entrance is to be commended. During the raising of the moles and their extension a gradual improvement will be obtained in the entrance depths, resulting in vessels of greater draft and length being .ble to enter the port. This will necessitate improvements in berthage and swinging room at Castlecliff to accommodate the vessels to the satisfaction of shipping masters, and it was with this in view that I recommended the extension of the basin wall and the dredging of the berths and swinging room in the basin. The swinging room in the river is limited, and additional width will be required simultaneously with the improvements at the entrance. My recommendation to dredge a por- ' tion of the basin, as shown on the plan, was subject to the silt being excluded as far as possible, by extending the basin wall. Using the Kaione for this dredging the Board would be employing her on work for which she was designed and which she has never had the opportunity of undertaking at Wanganui. My ideas were that as soon as the dredging and pumping ashore was completed to replace the Kaione with a maintenance dredger designed to suit the varying conditions existing in Wanganui. The decision of the Board to do no further dredging at Castlecliff, other than keep the berths open, will, under existing conditions reduce the dredging to a minimum, therefore the acquiring of a dredger at this stage of the works depends upon the amount of dredging it is proposed to undertake in other parts of the harbour. It would be advisable that an estimate be compiled of the amount of dredging to be carried out. With this information available the economics of the position can be studied. Unless a dredger can be kept constantly at work the dredging costs become excessive owing to the high capital charges for interest and depreciation. Mr Haszard’s Opinion. As requested I have the following remarks to make concerning the chairman’s loans proposals. The proposals are brought under ’ three headings which I will deal with seriatim. 1. Raising of North and South Moles.—l fully agree that this work is necessary and advisable in order to secure the very best scouring effects of the ebbing waters. 2. Extension of North and South Moles by 500 feet Each.—Proposals for extensions of the moles have been before previous boards. In 1914 the Board adopted proposals to extend the North Mole 1600 feet and the South Mole 1300 feet, which were approved by the Marine Department. However, of these extensions only 500 feet of .the North Mole and 200 feet of the South Mole has been carried out. Authority thus exists to extend each mole a further 110 feet from its present end. As it was thought very equivalent results could be obtained by the expenditure of a much lesser sum than would have been required for the 1100 feet extensions. I embodied proposals in a report dated 29/1/29 to the ex-chairman in which the North Mole was to have been extended 400 feet and the South Mole 600 feet. The former would have been a continuation of the present mole in a straight line but the latter would have curved towards the North Mole so that the entrance width would have been 500 feet. In my opinion this is necessary to increase the nozzle effect and also counteract to some extent the tendency of the effluent waters to pull to the south during westerly weather. The depths to be expected would have been ’ about 28 feet at H.W.O.S.T. outside the entrance and 26 feet at H.W.O.S. . between the moles The late Mr Blair Mason considered this to be the limitable depth obtainable by natural scour, vide his report on March, 1925. Mr Lee’s proposal, which Mr Hogan has adopted for the extension of the moles, projects both of these on parallel straight lines, the reason given by Mr Lee being that such a course would allow for further extensions. (The construction of the South Mole on a curve as proposed by me would not preclude further extension if required). However, Mr Lee suggests that if necessary the entrance can subsequently be narrowed by a wooden structure —if the Board prefers this course I have no objection. The question of whether the South Mole should overlap the North Mole, Mr Lee states, can be decided as the • work proceeds. lam definitely of the opinion that the South Mole should project at about 150 to 200 feet beround the North Mole, particularly as it is proposed to extend both moles in parallel straight lines. Mr Lee in his report stresses the necessity for taking steps to reduce the amount of siltation in the Castlecliff Basin, a matter to which the Board’s attention has been directed by me on previous occasions. Mr Lee and myself agree in principle that the only method of so doing is by narrowing the entrance to the Basin —but we differ in detail as to the manner in which this should be done. However, it is not proposed to carry out any work of such a nature until it can be ascertained what depths result from the raising and extending of the moles; the method of narrowing the entrance to the Basin can be reviewed later. The Board will understand, of

course, that until swinging room is increased at Castlecliff, a larger class of vessel than at present cannot be accommodated there. 3. Purchase of New Dredge.—The dredging problem at Wanganui may be set down under three headings: (1) Dredging Castlecliff Basin; (2) dredging in River Channels; (3) dredging at entrance (to restore normal depths). Note: Whatever ultimate depths may be obtained by an extension of the Moles there are bound to be fluctuations above and below what would be considered the normal working depth. Unfortunately I do not think it possible to obtain a single dredge that is suitable for satisfactorily performing all three operations. A self-contained combined bucket and suction dredge could be designed for performing operations (1) and (3) but owing to its draft could only work in the river channel at about high water. On the other hand a pontoon bucket dredge with independent seagoing hoppers, either self-propelled or towed, would be very suitable for all dredging except at the port entrance. -Whilst very reluctant to forego the ad vantages of being able to dredge at the entrance I consider that when the time arrives to obtain another dredge a pontoon bucket dredge of light draft together with independent hoppers would be the most generally useful tool for the Board’s operations.