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Bridge Foundation Scouring Scenario of New Zealand

In simple word, scouring involve removal of material from river or other stream bed and bank of them as well, form foundations of bridges and essentially these are happened due to water flow. We will learn elaborately about scouring, its types and measures to avoid such phenomena.


Scouring results maximum damage to bridges and consequent failure of many bridges all over the world. Now we will learn some failures in New Zealand. Here we will discuss about some failures of bridges related to scouring failure-
Site plan of Bull’s Road Bridge
  1. Bull’s road bridge
  2. Waitangitaona river bridge
  3. Blackmount bridge
  4. Waipaoa river rail bridge
  5. Oreti river bridge
  6. Bullock creek bridge etc.
Of these we will discuss first four bridge failures.
Collapsed Bull’s Road Bridge

a. Bull’s Road Bridge


Location:
  • On Rangitikei River
  • State highway -1

Failure date: 15th June in 1973

Causes of failure:
  • Scouring produced one pier to collapse
  • Structural hinging

Waitangitaona River Bridge:

Location:
  • On Waitangitaona River
  • State highway-6
Failure date: 12th march in 1982

Causes of failure:
  • One pier washed out
  • Two spans of this bridge lost due to accumulation of debris resulting severe scouring with flow concentration around these pier.
Site plan of Waitangitaona River Bridge

c. Blackmount Road Bridge:


Location:
  • On Mararoa River
  • Road from clifden-manapouri

Failure date:

Considered failure between (25-26) august in 1980 

Foundation scouring of Blackmount Road Bridge
Causes of failure:

Scouring, undermining in a pier.

d. Waipaoa River Rail Bridge:


Location: 
  • On Waipaoa River
  • On Palmerston north to Gisborne line

Failure date: between (7-8) march in 1988

Causes of failure:

  • One abutment outflanked and undermined
  • Three piers were affected under both general scour and local scour.

Construction of rail bridge on Waipaoa River
Regarding cost involvement, we can include an expenditure calculation, done by Department of Scientific and Industrial Research (DSIR). This report prepared by coleman and Melville in 2000. An annual expenditure of 36 million dollar (NZ) was involved to restore flood scours.


DSIR, New Zealand provided that 50% of its budget was required for restoration of bridges and maintenance of them as well. Of these 70% expenditure was concentrated to bridge scour. Besides these there have many indirect expenditure and long term impact on local economy.

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