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Civil EngineeringWBPSC AE · SSC JE · RRB JE

Hydrology— Important Topics, Formulas & MCQs

Engineering Hydrology studies the occurrence, distribution and movement of water — precipitation, runoff, infiltration, hydrographs and flood routing. It is a moderate-weight subject with a mix of theory and numericals.

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Important topics in Hydrology

Hydrologic cycle & water budget
Precipitation — measurement, mean rainfall methods
Abstractions — evaporation, infiltration, evapotranspiration
Runoff & rational method
Hydrographs — unit hydrograph theory
Flood frequency & return period
Flood routing — reservoir & channel
Groundwater & well hydraulics
Stream gauging
Droughts & floods
Must-know

Key concepts & formulas — Hydrology

Return period & probability

P = 1/T per year; probability in two successive years = (1/T)².

Hyetograph vs hydrograph

Hyetograph = rainfall intensity vs time; hydrograph = discharge vs time.

Evapotranspiration

Measured by a lysimeter; estimated by Penman, Blaney-Criddle methods.

Reservoir routing

Peak of the outflow hydrograph lies on the recession limb of the inflow hydrograph.

Exam relevance

3–5 questions in AE papers; overlaps with Irrigation and Fluid Mechanics.

Study tip

Unit hydrograph and return-period numericals are the most asked — practise both thoroughly.

Worked example

Sample Hydrology MCQ

A storm has a return period of 25 years. The probability that it is equalled or exceeded in any one year is:

A. 0.04
B. 0.25
C. 0.40
D. 0.02
Answer: A. Probability of exceedance P = 1/T = 1/25 = 0.04. For two successive years it would be (1/25)² = 0.0016.

Common mistakes to avoid

Probability over N successive years = (1/T)^N, not N/T.
Hyetograph = rainfall intensity vs time; hydrograph = discharge vs time.
Evapotranspiration is measured by a lysimeter (evaporation by a pan).
In reservoir routing, the outflow peak lies on the recession limb of the inflow hydrograph.
Keep going

Related Civil Engineering subjects

Strength of Materials
RCC
Steel Structures
Soil Mechanics
Foundation Engineering
Surveying
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