THE WAIAPU BRIDGE.

Poverty Bay Herald, Volume XLIV, Issue 14244, 12 March 1917, Page 4

THE WAIAPU BRIDGE.

FURTHER FLOOD DAMAGE.

Apart from the serious difficulties in the. matte* of reinstating important road facilities, the Waiapu County Council, as the outcome of the recent flood, is faced with a grave and expensive problem in ednnection with the Waiapu bridge. This structure, which spans the extensive Waiapu river between Wai-o-matatini and Tikitiki, is easily the largest bridge on the East Coast; apart from the lengthy approaches, the Waiapu bridge measures practically 940 feet, or more than three times the length of the Whataupoko bridge at Peel Street. When the Waiapu bridge was originally erected it comprised nine spans each of 82ft in lqngth, and. sauce theu it has not only been raised, but lengthened by an additional 144ft by the erection of four short spans, replacing a portion of (he earth approach washed away about two yearn ago. The last flood, a fortnight ago, made another breach in the approach in the southern or Wai-o-matatini approach, about 120ft between the bank and eni of the bridge having been reported to have been completely swept away. This, from what caii be gathered, will necessitate further lengthening of what is already an unusually lof.g bridge for this portion of the district. What, however, is the most gevious aspect of the whole matter is that there is apparently a substantial rise in the level of the recurring floods in . the Waiapu \Valley. When the bridge wa s originally erected, about three years ago, the usual precautions were taken to keep the structure well above flood level. The highest flood level, according to the County Engineer's data, is shown on the .plans as 10ft above the normal water level: In erecting the bridge which the Waiapu County Council did with the aid of Government grants, a "margin of seven feet wa's allowed between the then highest flood level and the decking. itlie bridge had* no sooner been completed, however (being opened in May, 1914), than a flood took place, rising over the decking. In addition to the lengthening* mentioned, the entire bridge was raised a further three feet, entailing an expenditure of probably £2000. With the bridge thus raised to a 'height' of 20ft above normal water level the "flood 'water came over the decking once more during last month's flood, beside' carrying away the earth approach mentioned. A singular fact about' the recent flood wa s that although tlio flood level at the approaching ends of the bridge was several feet below actual deck leV'el at the ends, the water towards the centre of the bridge is reported to have lapped over the decking, clearly showing that the Waiapu rivev, in time of abnormally high flood, has a considerable camber, to the extent prdbably of f6ur or five feet on the furface of the water. The phenomena will doubtless be specially interesting to those in engineering eifCjes concerned in bridge construction. On the Tikitiki side there is a short approach, but here in flood time the water is confined by higher ground. On the southern side, however, the bvidge is apprbached by a long stretch of manuka flat and in flood time the Waiapu river expands over this to a' width of approximately quarter of a mile." Erected on ferro-concretc piers, the s»uper«tructure is built of hardwood timber, the piles being driven thorugli loose shingle for several feet into- soft rock. ] The fact that one of the piers is re- , ported to have subsided a foot or so woWld indicate that }.he ( pjles were • not driven 'sufficiently into the . Local bodies erecting extensive bridge* in the past have occasionally been inclined to complain and protest against the apparently unnecessary substantial nature of the standards set down by the Pnbltc Works Department in^ the case of Government assistance with the work but in the light of recent experience generally it has been demonstrated that this policy is not only deeirablo

and that bridge structures should be most substantial, but it is false economy to attempt to erect cheap bridges where subject to extraordinarv floods. , It is understood the District Engineer, Mr Armstrong, is proceeding to the Waiapu this week to inspect and report upon the condition of the Waiapu bridge.