Questions
4 questions
Difficulty
Medium
Importance
Medium-high yield for NTPC and BHEL
Overview
Irrigation Engineering and Hydrology focuses on the management of water resources for agricultural use and the quantitative estimation of water cycles. For PSU exams, mastering the empirical design theories for canals and stability criteria for dams is essential for solving numerical problems quickly. Candidates must prioritize grasping flow mechanics in non-erodible and erodible channels to excel.
Hydrological Cycle and Flood Estimation
This subtopic explores the continuous movement of water and methods to predict peak discharge for hydraulic structure design. The Rational Method remains the most frequent point of inquiry for small catchments.
- Hydrological Cycle components: Precipitation, Evaporation, Transpiration, Infiltration
- Rational Method: Q = (1/360) * C * I * A
- Assumption of Rational Method: Rainfall intensity is constant over the time of concentration
- Time of Concentration (tc): Time taken for the entire catchment to contribute to the outlet
Canal Design: Kennedy vs. Lacey
Canal design involves calculating dimensions for stable channel flow using silt-carrying capacity theories. Understanding the subtle differences between Kennedy's critical velocity and Lacey's regime theory is vital for PSU numericals.
- Kennedy's Theory: Vo = 0.55 * m * y^0.64
- Lacey's Regime Theory: f = 1.76 * sqrt(d_mm)
- Lacey's Velocity: V = (Q * f^2 / 140)^(1/6)
- Hydraulic Mean Radius (R) in Lacey: R = 5/2 * (V^2 / f)
- Lacey's Bed Slope: S = (f^5/3) / (3340 * Q^1/6)
Irrigation Efficiency and Dams
Irrigation efficiency measures the ratio of water utilized versus supplied, while dam stability analysis ensures structural integrity against forces. Focus on the failure modes of gravity dams and seepage control in earth dams.
- Water Application Efficiency: (Water stored in root zone) / (Water delivered to field)
- Gravity Dam Failure Modes: Overturning, Sliding, Tension at base, Compression
- Middle Third Rule: Resultant force must lie within the middle third to avoid tension
- Earth Dam Seepage Control: Chimney drains and downstream filters
Formula Sheet
Q = (C * I * A) / 360
Vo = 0.55 * m * y^0.64
f = 1.76 * sqrt(d_mm)
P = 4.75 * sqrt(Q)
V = (Q * f^2 / 140)^(1/6)
R = 5/2 * (V^2 / f)
S = (f^5/3) / (3340 * Q^1/6)
Water Conveyance Efficiency: (Water delivered to field) / (Water diverted from source)
Exam Tip
Memorize Lacey's regime equations by heart, as most PSU questions require direct application of velocity, wetted perimeter, and bed slope formulas without derivation.
Common Mistakes
- Confusing Kennedy's critical velocity ratio 'm' with Lacey's silt factor 'f' during calculations.
- Forgetting to convert units for the Rational Method constant when using metric units instead of CGS.
- Neglecting the effect of uplift pressure while calculating the factor of safety against sliding for gravity dams.
More Revision Notes
Ready to test yourself?
Play topic-wise Irrigation Engineering & Hydrology questions in Aspirant Arcade — gamified MCQ practice.
Download Free