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Civil EngineeringWBPSC AE · SSC JE · RRB JE

Irrigation Engineering— Important Topics, Formulas & MCQs

Irrigation Engineering covers the supply of water to agricultural land — water requirement of crops, canals, headworks, diversion and storage structures. It is theory-rich with several standard numericals (delta, duty, silt factor).

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Important topics in Irrigation Engineering

Water requirement — duty, delta, base period
Methods of irrigation
Canal design — Kennedy & Lacey theories
Lined & unlined canals
Headworks, weirs & barrages
Cross drainage works
Diversion & storage head works
Dams — gravity & earthen
Spillways & energy dissipation
Waterlogging & drainage
Must-know

Key concepts & formulas — Irrigation Engineering

Duty-delta relation

Δ = 8.64B/D (Δ in m, B = base period in days, D = duty in ha/cumec).

Lacey's silt factor

f = 1.76√d, where d = mean particle size in mm.

Best canal section

Hydraulically most efficient is semicircular; trapezoidal is adopted for practical lined canals.

Crop delta

Rice has the highest delta (greatest water depth requirement) among common crops.

Exam relevance

4–6 questions in AE papers; standard formulae make it a reliable scoring area.

Study tip

Lock in duty/delta and Lacey/Kennedy theory — these produce the bulk of irrigation MCQs.

Worked example

Sample Irrigation Engineering MCQ

If the base period is 120 days and the duty is 1728 hectares/cumec, the delta (in metres) is:

A. 60 m
B. 6 m
C. 0.6 m
D. 0.06 m
Answer: C. Δ = 8.64 B / D = (8.64 × 120) / 1728 = 1036.8 / 1728 = 0.6 m.

Common mistakes to avoid

Duty-delta relation: Δ = 8.64 B / D, with B in days and D in ha/cumec.
Lacey's silt factor f = 1.76 √d, where d is the mean particle size in mm.
Rice has the highest delta (greatest water depth) among common crops.
Best canal section: semicircular in theory, but trapezoidal is adopted in practice for lined canals.
Keep going

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