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Old 09-04-19, 03:43
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Tony Smith Tony Smith is offline
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Join Date: Feb 2003
Location: Lithgow, NSW, Australia
Posts: 4,503
Default Bailey Bridge washed away in flood

On NZ's West Coast heavy rainfall has washed away a 30 year old Bailey Bridge. The bridge crossed the Waiho River, the stream flowing from the Franz Josef Glacier.

Due to Climate Change, or not, the Glacier has retreated a couple of kilometres in the past few years and deposited a huge amount of gravel and boulders in the river bed. Since the early 1980's, the riverbed of the 18Km long river has filled with gravel and risen 6.5m, altering the floodpain and where storm runoff can escape. It is now channelled under the bridge.

On 24th-25th March, a storm brought 1086mm of rain in 48hrs (over 40 inches!), flushing the Franz Josef valley and rolling bouders down the river bed.

With 8.2m of water under the bridge over a 200m width of riverbed, the forces on the bridge were massive. Despite this, the bridge withstood the force of water and boulders, but was ultimately destroyed by the north riverbank being scoured away. Instead of just dropping the 1 span that was supported at that end, the strongly connected design of the Bailey Bridge dragged 4 spans into the river.

In view of that excellent performance, the new replacement will be another Bailey Bridge, to be built by the Army!
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