THE MANAWATU BRIDGE.

Shannon News, 19 May 1922, Page 3

THE MANAWATU BRIDGE.

REPORT BY SHANNON BOROUGH

ENGINEER. At a recent meeting tlie Shannon Borough (Council instructed its engineer (.Air R. Edwards) to report on the condition ol the bridge over Hie Manawatu between Shannon -and Fox-

ton, and the condition pi' the Manawatu River in the vicinity ol the midge site itsell. This report was laid before the Borough Council on Tuesday evening. Mr Edwards -stated that the bridge was urgently in need ol considerable repairs, and 11 not attended to immediately would be completely ruined. The main faults were the asphalt on the deck, which had worked into holes, the effect ol which \yas to retain wet patches on the’ woodwork and so cause rapid decay. The timber and ironwork required painting, the want of which was causing the timber to perish. Tlie original design provided a light, easterly sliorecend pier resting upon a single row of piles driven into the river bank. This abutment pier was on dry land (luring the normal summer level of the river, but at the present time was about 50ft out from the solid bank and in Bft of water, which was rapidly deepening owing to the deflection of the current, to the west side of the stream, caused by a serious erosion higher up. A decided oscillation vas experienced whenever a.light vehicle passed over the bridge. The abut'ment pier was not intended to resist the impact of floating bodies such as brushwood and logs. There was considerable scour of the river-bed at this point; indeed, Mie eat fit approach when examined on April 22- last was crumbling and lading . into the stream. It this pier was neglected any longer it would assuredly be carried away, and tlie destruction of the easterly end span may result in the loss of the other three spans. The parts oi the bridge in immediate danger were the pier referred to and the temporary approaches. The west end at present was quite safe. The abutmen pier was in solid earth 175 links back from the water at normal level. The Manawatu River in this district flowed through a low-lying deltoid flat on a very soft bed. It would be seen at once' the river hanks In that locality offered comparatively no resistance to the flow ot water where there 1 was any deflection of the current. The exceedingly acute angle ,oi the river at a point above the bridge .was die immediate cause oi the uosion at that point, from which it rebounded and caused the set of tlie current to strike lire eastern hank ai the laulty pier referred to. This deflection of the current was quickiy shilling the deep waters ol the channel to the eastern side, 'iliis may be termed the immediate and direct result. of the rapid erosion taking place above the bridge, and would result in a -serious erosion at and below the eastern end, wiilst the western end would also be eroded. The bairns would be so distorted by alternate erosion that it_ would be next to impossible to maintain any bridge at the present site unless the erosion was permanently arrested. Tlie set of the current at present was direct on to the western bank, at some distance above the bridge. This portion of the hank had been eroded about nine chains within a few years, and to the extent of -about. 26 chains in 30 years, and there was strong evidence that in the future this rate of erosion would continue. The temporary wooden structure' at the eastern end was very unsatisfactory, and, like- the faulty pier previously „ relerred to, would he swept away by the first heavy j flood.

Mr Edwards made the following suggestions: (1) That another span Mid complete approaches be added to the eastern end of the bridge, also that the bridge he thoroughly overhauled, painted and repaired; (2) that the control of the river be vigorously .taken in hand with a view to arresting the erostion of the river banks, followed by planting and cultivating the right kind of willows along the banks; (3) tiie wotk must be taken in hand'immediately.