Q. Explain Foundation design discharge for a bridge?
To provide for an adequate margin of safety against any abnormal flood exceeding the design discharge (Q), the foundations, protection works and training works shall be designed for a higher flood discharge. This discharge shall be computed by increasing the design discharge (Q) estimated for waterway shall be based on (a) actual hydro-meteorological observations of the same or similar catchments (b) the computed flood with probable recurrence intervals of 50 years. The recurrence interval can be modified at the discretion of Chief Bridge Engineer based on the importance of the line.
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i)
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Catchment upto 500 sq.km.
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30%
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ii)
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Catchment more than 500 sq. km. and upto 5000 sq. km.
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30% to 20% (decreasing with increase in area)
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iii)
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Catchment more than 5000 sq.km. and upto 25,000 sq.km.
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20% to 10% (decreasing with increase in area)
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iv)
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Catchment more than 25,000 sq.km.
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Less than 10%(at the discretion of the Chief Bridge Engineer).
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