- 2080 Baisakh · 4 marks
Need of engineering hydrology in bridge design
Short answer
Engineering hydrology supplies design flood discharge, high flood level, waterway opening, and scour depth. These determine bridge span, deck elevation, and foundation depth. Without hydrologic data, the structure would be unsafe or uneconomical, risking failure from floods.
As a civil engineer how do you justify the need and importance of Engineering Hydrology for the design of Bridge?
A bridge crosses a river, so its safety depends on how much water the river carries and how high it rises. Engineering hydrology supplies this information.
Need and importance
- Design discharge: The peak flood for a selected return period (for example 100 years for major bridges) is found from rainfall-runoff relations, rational method, unit hydrograph or flood frequency analysis of gauged data.
- Design high flood level (HFL): From the discharge and the cross-section (rating curve), the HFL is found. The bridge deck level is fixed above HFL with a freeboard.
- Waterway (linear opening): The span and number of piers are chosen so that the flood passes without excess afflux, using the discharge and regime width (Lacey).
- Scour depth: Scour depends on discharge per unit width and silt factor, and decides the foundation depth of piers and abutments.
- Afflux and backwater: Narrowing the channel raises the upstream level; this needs hydrologic and hydraulic computation to avoid flooding upstream.
- River training and protection: Guide bunds, spurs and pitching are based on flow and flood data.
- Economy and safety: An underestimate causes overtopping, scour and failure (common in Nepal's monsoon), and an overestimate wastes money.
A civil engineer therefore cannot fix the span, deck level or foundation depth without hydrologic data.
✓ Answer checked by Claude Sonnet 5.5
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