THE SHANNON BRIDGE.

Manawatu Herald, Volume XLII, Issue 2165, 19 August 1920, Page 2

THE SHANNON BRIDGE.

ENDANGERED BY EROSION

The danger that threatens (ho main traffic bridge over (he Manawatu river on the Shannon-Fox ton road by erosion at the eastern approach was brought under the notice of the Horowhenua County Council on Saturday, first by a reference to the matter by the acting-inspec-tor, Mr 0. Catley, and later by a full report on the posit ion by Messrs A. W. Climie and Son, civil engineers, of Hastings. Mr Catley stated that the bridge, as reported by letter, was in a. rather serious danger of having (he approaches on the eastern side daniaged by erosion. The bridge had been examined by Mr Climie, juur., who would report fully on the mutt er.

Mr CJimie’s report was as follows

“An examination of the river, in (he neighbourhood of the hridg* shows by comparison with the original plans and photographs, that the main stream has shifted from (he west to (lie cast side' of tho bridge, and what were their designed as laud piers are now in deep water. - This change arises from an ‘S’ bend having f'ormed in the river

about (ifteen chains above the bridge, and which with every Hood B becoming more prominent. It is not only deducting the flood water cii to the eastern approach, but is, threatening to isolate the bridge entirely. The training of a river of this size into a proper course is a. work of such magnitude that wo assume it is beyond the province of vour Council. Instead of remov-

mg Iho cause of the 1 rouble, it is only possible, therefore, for them io construct works to prevent fnrIher erosion in (lie neighbourhood nf the bridge. The inunediale nev-er-sit y is to defleet: I lie Hood water from the eastern approach and the protective works should lie so designed that .they not only do this but also encourage a deposit of silt io replace the materia! scoured from around tho eastern piers. Considering: the sandy nature of Ihe, river hank ami hod, and the eomparafively great rise of Hood water, we are of the opinion that the only i vpe of groin capable of acting successfully is- one of piles of the design shown on Ihe accompanying plan. In view of the delay that would occur in procuring Australian hardwood, coupled with their high eosl, we recommend that locally grown bliu'gum piles be used. The groin need not be of a permanent ■nature, as we consider that the sand spit forming higher up on the eastern side will gradually reach the bridge as the K bend becomes more pronounced. The groin should be placed asbul one chain above the bridge, and at rigid angles to the stream. An embankment should conect it to the eastern approach to obviate any possibility of Hood water getting round the root of the groin. Should this occur it would become a menace instead of a protection to the bridge. A mattress of li-iree should he staked along the bunk in the neighbourhood of the groin to prevent erosion by eddies set up by the obstruction. We notice from the original drawing that the easlern piers are supported on comparatively short piles. These should be supplemented by 40 feet ironbark piles as soon as they can be procured. The totara ,sheet planking should be continued down to low wuler level. As mentioned above,-the'formation of the S bend will in course of time threaten to isolate the whole bridge. Apparently the iS bend is moving as a whole slowly towards the bridge. This danger, we consider, can only be overcome by Ihe const met ion of groins some distance above the bend to train the river into its original course. This work would be very costly, and probably beyond the resources of your Council.’’ Cr. Whyte stated llial the position was not so bad now as it was some time ago.

Cr. McLcavcv said that the idanawatu County should be asked to send their engineer to have a look at the bridge. That body was as much concerned as llorowlienna v, as. They would also have Ibo advantage of his opinion. The chairman (Cr. Alonk) said llorowlienna was the controlling body, but Manawalu was respon--ibie for halt The cost of whatever work was contemplated. The chairman explained that he had taken id ion to got a report’ from Air Mimic on information supplied by heir inspector (.Mr Catiey) on tlie ‘ondition of (he bridge. He bad herefore decided to act at once, and ;■<>( Air (Timic to report. The report vas now before the Council. The •hairman suggested that as their iwn engineer was due in a few days hey might wait until he hud inspected the bridge, so that the Coined would have the benefit of his opinion as well. To this the Council unanimously •tgrfeed, and on Cr. Ha fitness’ motion the chairman's action in calling in Air.Climie to report on the bridsgj was confirmed.- ft*