WAIWAKAIHO BRIDGE

Taranaki Daily News, 6 February 1917, Page 7

WAIWAKAIHO BRIDGE

ENGINEERS' REPORT. Messrs. Sladden mul Palmer, engineers, made a lengthy report to the Tarntiaki County Council yesterday on the. Waiwakaiho Bridge. The report showed that the bottom of the western cylinder pier was 25 feet below the spring of the. arch of the bridge, or about 10 feet below wafer level and is resting upon a bed of pumice underneath the boulder formal ion. This pumice was so light when dry that it would float on water, but, quickly absorbed water and S'nks When saturated with water this looked like a soft sandstone of a blue prav color which 110 doubt accounted for the statement that the cylinders wort carried down to a sandstone formation. They felt justified in stating that the cent's pier, which was undermined some years ago, is resting on the same foundation, as is also the eastern cylinder pier which is 10 feet below water level. It would have been too expensive to get ai the bottom of this pier. The western abulment, is down about 4 feet below water level and about 0 feet above the pumice formation.

They therefore made the following suggestions for re-instatcment of brokcA .span and general protection of the bridge:—(a) that, a wier below the bridge is essential; (b) that the western P.outnient be carried down to the pumice bed; (c) that the western cylinder pier and the centre concrete pier are safe enough provided a wier is built without undue delay; '(d) that the deep hoi.' round the eastern cylinder pier be filled up with the broken concrete of the old span, and that fresh concrete be rammed in round the bases of the cylinders. This would hasten the filling up of the river bed after the weir was in position; (e) a ihw abutment and wing walls to be I'iiill at the eastern end and Ihe foundation carried down to bottom, the new bridge span to conform to the design of the present structure, at any rate as far as external appearance is concerned; (f) remove the :onoretc now hanging between the cylinders of the eastern pier. This concrete .'an now serve no useful purpose, and is indeed rather a menace to the saiety of the pier, as the two cylinders were supporting an unnecessary weight of from 20 to 25 tons. Their revised estimate of the cost was £1.)50 for everything. They pointed out that there was an average fall of six inches per chain in the river for about 24 chains below the bridge, and it 'was, obvious that the scour and consequent lowering of the river lied would continue and the process would he hastened as long as the local authorities obtain their supplies of road metal from the river. The pumice foundation of the bridge piers is not good enough to withstand any scour should the river ever get down to that level. A weir would be preferable to any attempt to carry the foundations down to get a really good foundation. Considerable care should be exercised in designing .he, pronosed weir. They considered that some adequate apron should be provided on the down side ami the question of going down to a foundation was most important and •worthy of serious consideration.

The New Plymouth Town Clerk wrote! that the Borough engineer hurt expressed some anxiety as to whether the. construction of the proposed weir might not so raise the bed of.the river that in tho event oF another severe flood an overflow might take place on the low flat lands adjacent to the bridge, causing damate for which compensation might be claimed from the Council, and suggesting that this should be placed before the Engineer-in-Chief. Messrs. Sladden and Palmer stated that Messrs. Grayling and 'Parkin were prepared to undertake the work on .1 comission basis, supplying all plant. The Borough Council also wrote later agreeing to pay cue third of tho cost of the work subject to the plans, specifications and estimates being approved of by the Borough engineer and Borough Council. Under date. January 24 Hon. W. Fraser, Minister of Public Works, telegraphed that he had approved of the cngineer-in-chief's recommendation that Messrs. Sladden and Palmer's report be adopted as regards restoration of the bridge and abuttnient, and also that the weir be lowered and construction slightly modified. This modification was being dealt with Tiv the district engineer, and the engineer-in-ciiief also recommended the County Council and the New 'Plymouth Borough Council should endeavor to arrange with the contractor for the weir to restore the bridge. lie undertook to provide one third cost of constructing the bridge, provided that such cost did not exceed £1(100, and that the recommendations of the engin-eer-in-chief had been given effect to. The chairman (Mr. ,T. S. Connctt) reported that the Engineer-in-Chief, Mr. Holmes, and Mr. Sharp, Public Works Engineer, Stratford, visited the bridge 011 January 2fi, accompanied by representatives of the Council and of the Borough of New Plymouth. Messrs. Sladden and Cook, the respective engineers were also present, and their reports previously-prepared were submitted for consideration. The whole of the question of foundations and Repairs to bridge and completion of the weir was thoroughly discussed. and at a subsequent meeting of the engineers mentioned, it was unanimously decided to recommend that "the eastern and western abutments be carried down to correspond with the cylinder foundations and that the plan 01 the weir be slightly moiliiiod to suit altered conditions, brought about, by the very heavy flood recently experienced.'' As it was felt that this 'recommendation wouUl meet with the approval of the Council, it was immediately wired to the Minister of Public Works with the request that he would contribute a portion of the cost. In reply, he agreed to pay one third on condition that the County and Borough contributed a like amount,, and so that the weir might be completed as soon as possible, he suggested that the foundations of the bridge be at oiu-e proceeded with by dav labor ami that Mr. Parkin, contractor for the weir, be engaged under the supervsision of Mr. fliavling. This repiy was at once submitted to a special meeting of the Xew Plymouth Borough Council and received its approval. With the sanction of the subcommittee the recommendation had been given effect, to ar.d the preparatory work of removing debris, was commenced on January 2!'.