MANAWATU RIVER

Manawatu Standard, Volume LVII, Issue 71, 23 February 1937, Page 7

MANAWATU RIVER

CONTROL PROBLEMS. PALMERSTON NORTH BOARD. '' The monthly meeting of the Palmerston North River Board was held yesterday. Those present wore: Messrs A. E. Hansford (chairman), J. Hodgens, M.P., G. Tremaine, J. T. J. Heatley, W. Anderson, Jos. Batchelar and W. R. Hoperoft. The Manawatu-Wairarapa Employers’ Association wrote inquiring if the board employed an engine-driver. —lt ‘ was decided that the clerk (Mr J. R. Hardie) investigate the classification of engine-driver and advise the association accordingly. The foreman (Mr A. Lane) submitted the following report, which was adopted:—“Mcßae’s Bend: The extension of No. 10 groyne 85 feet is completed. The cost was £52 10s and the cost per foot £1 9s 9d. The driving of two piles and fitting of three stays and replacing two booms and side braces on No. 12 groyne at Mcßae’s bend has bqen carried out as authorised. The cost was £33 6s 4d. Opposite Cresswell’s foreshore: The driving of the pipes for the explosives, the blasting of the river beach and constructing approximately 220 ft of a solid wall two feet high to help to concentrate an extra volume of water on to the loosened area, has been completed. The cost was £57 ss. On completion of the groyne work at Mcßae’s bend, the plant has proceeded upstream to Gosling’s East and has commenced driving the piles for the extension on three groynes. The totara logs that were anchored opposite Cresswell’s foreshore have been split into boom timber and transported to Gosling’s East for the works on hand. Sufficient timber for the completion of the extension has been delivered on the site. The cutting and hauling of the trees for the brush groynes at Cresswell’s is in hand. The repairing of 40 chains of fences has been carried out during the month on Mcßae’s foreshores and Gosling’s East. The weather and river conditions for the month have been favourable for the progress of works —the highest rise being Bft. on February 15.” —The report was adopted. Messrs Heatley and Batchclar commented on the cost of operations opposite Cresswell’s foreshore. Mr Heatley said that the cost had been £7 5s more than was authorised. He criticised the method of using explosives. The advisory engineer (Mr A. Fisher) said that the building of the training wall had accounted lor the extra cost as it had been longer than had been anticipated. The eight foot flood that was experienced had not scoured the accumulation, but had rather added to it.

The chairman said thq work had not been as effective as had been hoped, and board members were evidently disappointed. Mr Hoperoft said the work had been clone at the instigation of the board, and against the engineer’s inclination. All the board could do was to confirm the expenditure of the extra £7 ss. It had experimented and had failed. The expenditure of the £7 5s was confirmed. REVIEW OF WORK. The report of the advisory engineer (Mr Fisher) was adopted as follows: — “In accordance with the board’s instructions, the shingle deposit in the river channel opposite Cresswell’s foreshore has been well loosened by means of explosives, and all. the logs affecting the free flow of the river have been removed. To facilitate the scour of the shingle deposit, I considered it necessary to concentrate the flood run of the river on the point affected by means of a training wall made of sacks filled with shingle. This wall is projected upstream at a suitable angle, its length being 220 feet and height 2ft 6in. There is a sharp fall in the river-bed of sft in four chains toward the point of erosion in the river bank and I believe this condition will dominate the attempt made to produce the effective scouring action required to displace the shingle deposit. However, the result will be determined by 'sufficient flood action. For the boards information I desire to review briefly the physical conditions of the river channel affecting the control of the river: (I) It is significant that oiling to the frequency of high floods during the last 18 months the convex bodies of shingle deposits in the river channel have greatly increased by the excessive downward movement and mdgment of shingle. This is characteristic of all shingle bearing rivers of high flood volume and velocity. (2) it is therefore obvious that where excessive contraction of the normal liiei channel caused thereby occurs, an extension of the existing groyne system is imperative. (3) In this respect it is certainly the right policy to utilise and train the immense available hydraulic flood power of the river to reduce or remove restrictive formations in tlie river channel which are directly lesponsible for the erosion of the river banks and for this purpose the open boom groyne operates effectively and economically. (4) Reverting to the locality in question above (Child Bros, shingle works) the opposing body ot shingle in the river channel has not only greatly increased in area and height, but has also developed extensively upstream, and this is the most critical feature. Besides, a relief channel that formerly existed along the left river bank' is now completely filled with shingle. This condition applies in like manner to the opposite convex body immediately above (on the citv side) and the combined effect of these conditions has caused a definite contraction of the normal river channel culminating in a confined intense scour of the river bed, and thus producing a steep gradient towards its ri'dit bank in the vicinity of Cresswell’s foreshore, thereby causing erosion of the river bank. Unless the prevailing hydraulic power intensified hv gravity at this point is checked and diverted from the point _of attack by means of groynes as previously advised, the present adverse conditions will predominate and develop. Technically, the law of gravitation will prevail and must be harmoniously respected. \tr Tremaine asked whether the board would attempt scooping the shingle bank, as had been done at the Fitzroy bend. Would, the board do anjthing ‘further? ... . ' . The advisory engineer said that the scooping at Fitzroy bend had proved to be a failure. A channel had also been put in the bed now referred to, but had not had any effect, in his opinion the only way to shift the accumulation was to direct the livei at it by the installation of two groynes. Mr Heatley said that the groynes at Mr Anderson’s holding had not shifted metal accumulations, and the advisory engineer said that they had carried out their purpose in protecting the bank. Mr Heatley remarked that evidently more and more groynes would be required. The chairman thereupon commented that in that case the building of groynes would never be done with. When asked by the chairman, the advisory engineer said his opinion was that all that could he done had been done to induce scour opposite Cresswell’s without the construction of two

groynes He did not think that anjthing should be done tins financial year in view of the condition of the board’s finances. Three brush groynes were now being constructed in an endeavour to assist the river to scour. Tho chairman agreed that nothing should he done until the financial year had ended. . , , The discussion was not carried iurtllTlie treasurer reported that the board had a credit of £452 15s Bd. The outstanding rates amounted to £3OO 14s 6d and the arrears of rates to £205 12s 3d.