Protecting City From River Erosion

Manawatu Times, Volume 60, Issue 231, 1 October 1935, Page 9

Protecting City From River Erosion

PALMERSTON NORTH BOARD MEETS At the meeting of tho Palmerston North River Board yestorday there were present tho Mayor (Mr A. E. Mansford), Trustees G. Tremaine, J. Ilodgens, J. T. Heatley, W. Anderson, W. E. Hopcroft and J. Batchelar. Also in attcndanco wero Messrs E. Eisher, advisory engineer, and A. Lane, works foreman.

The Board’s foreman (Mr A. Lane) reported as follows; —Eitzroy Diversion Channel: The repairing of No. 4 groyne is completed aud the driving of the piles for tho extension, as authorised, is in hand. Tho construction of the groyno adjoining tho Esplanade is* completed—length 00ft, cost £132 • 10s, cost per foot, £1 9s 4d. No. 5 schomo men have been engaged on the following work: Cleaning and levelling around the trees, repairing fences, willow planting on the low levels between Ruahine street aud Brightwater terrace, and planting approximately 300 pino trees on the foreshore below Gosling’s west. Tho necessary alterations to tho fences for the protection of the trees has also been carried out by these men. General: On completion of the groyno work at Eitzroy bend it is advisable to carry out certain repair work to the derrick on No. 1 plant before proceeding upstream to commence further groyno work at Mcßae’s bend. The blasting of tho logs which obstruct the regulation channel at Fitzroy bend and above Child Bros, works have been carried out periodically when tho conditions were suitable. The action of recent floods accounted for some erosion behind No. 1 groyne at Stuart’s bend. This breach is being checked by means of brushwork; practically all the material is being supplied by Mr Stuart. The frequent occurrence of Hoods and adverse weather conditions that have prevailed during the month have had tho tendency to retard the progress of groyno work. Two freshes were recorded, the highest being 10ft on tho 11th. instant.

Anderson’s Bond The board’s engineer (Mr E. Eisher) presented a special report on the condition of river control works at Anderson’s bend, and river channel conditions generally. He said that ho had carefully examined tho river bank protection and regulation works at Anderson’s bond. Tho opening disclosed during tho recent flood period on the ground surfacb at a point at the back of tho riverbank protection works, a matter which caused tho board sonio concern, was thoroughly investigated. In this respect river soundings wero taken close to and covering tho affected surfaco portion of tho riverbank, recording the averago normal depth of water to bo four feet, which proves that no bed scour has taken -place, or, if so, that a filling has intervened during the flood period. However, under the present conditions, ho was fully satisfied that the bank protection works at this point were quito secure. According to indications and observations the aperture causing Concern was superficial■ and therefore not of a serious nature, and not likely to de-

velop. Owing to the present apparent weakness it was mentioned in a discussion of the matter by the board at its iast meeting, that as a relief measure the construction of a groyuo at a point upstream might bo considered advisable, henco tho cause for investigation. With duo deforonco to tho expressed opinion and in conformity with the present satisfactory condition of tho river bank protection works and channel in this bond, Mr Fisher submitted that even if required, a groyuo at the point suggested would not servo tho purpose required; rather would it tend to create a major damago to tho works at tho apparently weak point and generally would have a reactionary effect on this well planned system of works. Ha thereforo firmly advised the board to abandon this project as a remedial measure even if required in future. An additional top boom on No. 1 groyno to increase its efficiency was necessary and this ho would adviso tho board to do, otherwise tho system of works was giving the requisite service. Other Works. Mr Fisher reported that he had also made an inspection of Gosling’s bend east, where ho was pleased to report that the groyno works, as a result of tho recent high floods, had effected a highly satisfactory improvement in tho river channel, wieh augured well for progressive development in the direction desired.

Tho channel area from Mcßae’s bend down to tho Fitzroy diversion channel had also received attention. This reach was gradually responding to tho regulation works, w r hieh would bo facilitated with tho reparation of tho damaged •groyne works at the lower end of McRae’s bend, a w r orlc that had been held in abeyance longer than expected by reason of the continuous flooded state of tho river. With this work, completed, a definite improvement in the development of Fitzroy diversion channel would eveutuatc.

Speaking generally, thero was distinct evidence that tho river channel had been appreeialby improved throughout the Board’s district by tho regulation works, as a result of six successive abnormal floods since May last. This constituted a yearly record for the period of nine years past; consequently tho board’s works had withstood the severest test as yet imposed, remarkably well. Board’s committee inspection: The authorised inspection took placo on August 26 last. The objects of tho inspection were, first, the advisability of an additional groyne at tho Esplanade. This at present was considered unnecessary. Secondly, No. 5 groyne extension of two spans in Fitzroy diversion channel recommended by Mr Fisher at the last meeting. In this case tho board’s committeo decided that for the present this proposal be left in abeyance, and to receive future consideration if found necessary. Mr Fisher pointed out to the board that the river conditions at a point immediately below this groyne wero of a critical naturo and required closest observation.

Tho engineer was instructed to watch closely tho opening disclosed i%tho bank at Anderson’s bend. Trustees Hodgens and Heatley, when

speaking of tho dangers at Anderson's bend, disagreed with the engineer on the latter’s condemnation of an extra groyne higher upstream. They held that it would deal with the cause of tho trouble by cutting away the toe of the accretion on the opposite side and easo the water around tho bend. Tho engineer, however, contended that one groyne would not do that; it would need a series of groynes. One groyne would only throw tho water on to tho weak spot. A series of groynes was not warranted and would cost a considerable amount of money. It was decided to extend No. 1 groyne as recommended by the engineer. Trustco Heatley reported on the improvements that had developed as a result of blowing the logs out of the river at Child’s, and he advised going ahead with tho work. Statement of Rates. Bates struck, £2230; less payments to date, £IO2O 3s 8d; outstanding £1209 16s 4d. Arrears: Amount outstanding April 1, 1935, £665 19s 8d; less payments to date, £214 12s 2d; 7s Gd.