FOXTON-SHANNON BRIDGE

Manawatu Herald, Volume XLIV, Issue 2432, 23 May 1922, Page 1

FOXTON-SHANNON BRIDGE

REPORT OF SHANNON BOROUGH ENGINEER. .

•At a recent meeting the Shannon Borough Council intruded its engineer (Mr R. Edwards) to report on the condition of the bridge over the Manawatu between Shannon and Foxton, and the condition of the Manawatu River in the vicinity of •the bridge site itself. This report was laid before the Borough Council on Tuesday evening. Mr Edwards stated that the bridge was urgently in need of considerable repairs, and if not attended to immediately would be completely ruined. The main faults were the asphalt on the deck, which had worked into holes, the effect of which was retain wet patches on the woodwork and so cause rapid decay. The timber and ironwork required pointing,' the want of which was causing the timber to perikh. The original design provided a light, easterly shore-end pier resting upon a single row of piles driven into the river bank. This abutment' pier was on dry land during the normal summer level of the river, but at the present tinny was about 50ft. out from the solid bank and Sit. under water, which was rapidly deepening owing lo the deflection of the current to the west side of the stream, caused by a. serious erosion higher up. A decided oscillation was experienced whenever a light vehicle passed over the bridge. The abutment 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, the earth approach when examined on April 22 last was crumbling and falling into the stream. If this pier was neglected any longer it would assuredly be carried away, and the destruction of the easterly end span ‘may result in the loss of the other three spans. The parts of the bridge in immediate danger were the pier referred to and the temporary approaches. The west end at present was quite safe. The abutment pier was in solid earth 175 links back from the water at normal level. The Manawatu River in this district flowed through a lowlying deltoid flat on a very soft lied. It would be seen at once that the river banks in that locallity offered comparatively no resistance to the flow of water where there was any deflection of the current. The exceedingly acute angle of the river at a point above the bridge was the immediate cause of the erosion at that point, from which it rebounded and causey! the set of the current to strike the eastern bank at the faulty deflection and the current was quickly shifting the deep waters of the channel to the east side. This 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, while the western end would also be eroded. The banks would be so distorted by alternate erosion that it would next be impossible to maintain any bridge at the present site unless the erosion was permanently arrested. The set of the current at present, was direct on to the western bank, at some distance above the bridge. This portion of the bankhad 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 future this rate of erosion would continue. The temporary wooden structure at the eastern end was very unsatisfactory, and like the faulty pier previously referred to, would be swept away by the fix-st heavy flood. Mr Edwards made the following suggestions: (1) That another span and complete approaches be added to the eastern end of the bridge also that the bridge be thoroughly overhauled, painted and repaired; (2) that the control of the river be vigorously taken in hand with a view to arresting the erosion of the river banks, followed by planting and cultivating the right kind of willows along the banks; (3) the work- must be taken in hand immediately.