Proposed Spillway for Lower Manawatu River

Manawatu Times, Volume 59, Issue 214, 7 September 1934, Page 8

Proposed Spillway for Lower Manawatu River

RIVER BOARD DIVIDED AS TO FEASIBILITY. Further details of the proposal for tho by-passing of the Manawatu river near Foxton were submitted to tho authority controlling that portion of tho river—tho Mnnawatu-Oroua River Board—at its meeting yesterday, when Mr. H. E. Farquhar, civil engineer, submitted his report on the suggested undertaking. The report discussed the possibility of facilitating the discharge of flood waters by a spillway across the base of the Matakarapa peninsula between Hartley’s bend at Whirokino. It was claimed that such a scheme would in no wise impair Foxton’s qualities as a. port. The matter was first mooted to the board at its August meeting by Mr. R. J. Law, a member of the board. Mr. Farquhar was then asked to submit a report and plans sufficiently comprehensive to be submitted to the Public Works Department, should its aid be sought for the scheme. The proposed spillway would be one mile in length, and the distance by river between intake and discharge is <3 miles 20 chains. There would thus be a reduction of 5 miles £0 chains in the distance to be traversed by flood waters. Air. Farquhar’s report to tho board yesterday stated: — “It is suggested that the Foxton Harbour Board bo approached and serious, consideration given to reducing the height of tho weir crest to reduced level 4 feet; i.c., mean sea level. This would result in tho channel being tidal from half to full tide twice daily and would reduce tho menace of blown sand, tho channel becoming self-cleansing in addition to a considerable increase in its capacity for flood discharge. The tidal effect, which would not bo great, would bo to increase the volume of tho daily flood tide which would be felt higher up the river than under present conditions. “Access: The formation of one and a-quarter miles of road from the southern end of the Whirokino bridgo will be necessary to give access to the site. “Excavation: The bulk of tho materials to be moved consists of sand with a small percentage of silt throughout giving it some cohesion. Underlying the sand is a stratum of compacted silt and in places a foot of peat between tho sand and the silt. The level of tho silt at the inlet is about 6 feet reduced level and at the outlet 14 feet reduced level. Timber is in evidence mainly at the surface of the silt at Hartley’s bend, but is not evident at Whirokino bend. Tho excavation will reach the silt at Whirokino and be some 10 feet into and below the silt surface at Hartley’s bend. As stated in proposal one, the quantity of spoil to be excavated for a channel with 20 feet bottom width and side slopes one and a-half horizontal to one vertical is 300,000 cubic yards. To construct an efficient inlet as shown on the plan and grade the bottom of tho channel to give a fall at the rate of'two feet per mile, would increaso the quantity of spoil to 490,000 cubic yards. "Sand control: There are no open sand faces on the route of the proposed channel, 50 chains at the Mhirokino end being in a grassed valley between sandhills, and 50 chains at the western end crossing small sand-ridges covered by marram, lupin and gorse. Tho majority of the spoil can be dumped on the north-eastern side of the excavation—that is, on the side away from the direction of the prevailing wind, and so will not be a menace to the . channel. Owing to the possibility of *the wind action opening up sand-faces and drifts, a strip of land some 10 chains wide along the south-western side of the channel requires planting with trees —pinus radiata —as protection. Where necessary, excavated silt will be used to bind exposed sand-faces and brush fences used to control blowsand until fixed by marram or trees. “Spillway weir: Former surveys show that since ISSI there has been no material alteration by e-rosion of the loft bank of the river at the site of the proppsed spillway inlet. The plan shows provision for an effective weir crest of three chains width with future extension to six chains, while still further extensions may bo made in safe country not threatened by erosion, when development of the channel warrants them. The weir consists of reinforced concrete sheet piling up to 20 feet, long driven to reduced level minus 17ft.— i.e., approximately 7ft. below the present bottom of the river,at the inlet—with reinforced concrete cap and removable timber cap. Alternately steel sheet piling could be used with top encased in concrete. , “Scour adjacent to tho up and down stream faces of the weir may occur some years hence after the channel has developed, ia which case some protection would be required, but it is not necessary or advisable to undertake this work at present.’’ , The estimates for the various schemes submitted were:— Number One Proposal. Purchase of land, payment for severance, right of access, etc., £G00; construction of access road, £500; treeplanting, £200; eveavation of 490,000 cubic yards at Is. a yard, £24,500; weir, 4 j chains at £3OO a chain, £2250; total, £23,050. Number Two Proposal. Items as in No. 1 proposal, £23,050; channel with bottom widtli of 40ft., ad- ; ditional excavation 100,000 cubic yards • at Is. a yard, £5000; 3 chains of weir at £SOO a chain, £1500; total, £34,550. Number Three Proposal. Items as in No. 2 proposal, £34,550; - additional excavation to give R.C. 3 , feet, GO,OOO cubic yards at Is. a yard, £3000; additional foundations and five- ; foot gates, six chains at £SOO per chain, £3000; total, £40,550. i Mr.‘ Mitchell said that under present ( conditions ho did not think the job ] could ever be put through ns an unem- ] ployed undertaking. i Mr. Law concurred. Rather tho job | should bo undertaken by tho Public f Works Department, with permanent l labour, Jio said. %. 1 Mr/ Farquhar said he had since ascertained that the clerk of Foxton had j submitted similar proposals to the. Pu- t lie Works Department a few years ago. 1 The people of Foxton, it was thought, would not be averse to the present v

scheme provided the town's shipping facilities were left intact. Replying to sceptical inquiries by other members, Mr. Law instanced the success of the Eangataiki cut, declaring the current proposal would give comparable benefits. Mr. H. J. Lancaster said that to make the cut secure, more than clay would bo required to bind the sand. Mr Farquhar pointed out that at the necessary points concrete slabs would be placed for protection. Mr. Law said the clay was exceedingly hard and would bind effectively. There was a brief passage of arms between Mr. Lynch and Mr. Law. The former contended that tho board as n whole had always vacillated in its policy for years past, and was too readily swayed into spending ratepayers’ money on investigating new schemes. As far as he could see tho present proposal would cost, tho ratepayers a lot of money to little purpose,. As well attempt to co-opt Woodville settlers to contribute as expect peoplo in the Kairanga to pay their share for the present scheme. Mr. Law said members should view the board's area as a whole, and without parochial bias. Just recently the board had acquiesced in tho Hamilton ’» Bend project, and ultimately it would be duty bound to give so,rue relief to the lower basin. He did not wish to spend a shilling more than necessary, but thought the matter should at least be thoroughly discussed before the plan was discarded; The ratepayers could justly seek Government, assistance,, tis the scheme was essentially one of public import. Further consideration of the scheme ivas deferred.