Tamil Nadu PSC — Agricultural Engineering (Code 164, degree standard) · India · Tamil Nadu Public Service Commission
Original practice questions written to the published syllabus · not past papersHow much water a crop needs, when to give it, how to measure and convey it, and how to design surface irrigation.
In the exams: GATE AG Section 5 (irrigation depth, interval and command area in 5 of 8 papers 2019–26); ICAR AIEEA-PG Unit VII; ICAR AICE subject 43; NCEES PE irrigation; PRC ABE; IA CAIS
How our questions for Tamil Nadu PSC spread across the units of Irrigation Engineering (Soil-Water-Plant, Conveyance, Surface Methods). Difficulty: 28 easy, 21 medium, 1 hard.
| Command area development | 8 | |
| Design of irrigation channels | 6 | |
| Irrigation scheduling | 5 | |
| Water measurement: weirs, Parshall flume and orifices | 5 | |
| Canal lining | 5 | |
| Soil-water-plant relations: field capacity, wilting point and MAD | 3 | |
| Evapotranspiration and FAO-56 Penman-Monteith | 3 | |
| Border irrigation | 3 | |
| Basin irrigation | 3 | |
| Irrigation efficiencies and distribution uniformity | 3 | |
| Effective rainfall | 2 | |
| Furrow irrigation | 2 | |
| Crop coefficients and crop water requirement | 1 | |
| Underground pipeline systems | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In the gravimetric method, soil samples are dried to constant mass at what temperature?
A. 105 °C
Soil is dried at 105 °C (usually about 24 h) to remove water without burning organic matter. 60 °C is used for plant tissue and leaves water in soil; higher temperatures begin to oxidise organic matter and remove structural water.
Further reading: Michael, Irrigation: Theory and Practice
A wheat scheduling recommendation is an IW/CPE ratio of 0.8 with an irrigation depth of 50 mm. At what cumulative pan evaporation since the last irrigation should the next irrigation be given?
D. 62.5 mm
CPE = IW / ratio = 50 / 0.8 = 62.5 mm. 40 mm multiplies instead of dividing; 50 mm ignores the ratio; 80 mm confuses the ratio with the CPE.
Further reading: Majumdar, Irrigation Water Management
A 90° V-notch weir operates with a head of 0.20 m. Using Q = 1.38 H^2.5 (SI), what is the discharge?
D. 24.7 L/s
Q = 1.38 × 0.20^2.5 = 1.38 × 0.01789 = 0.0247 m³/s = 24.7 L/s. 123 L/s uses the rectangular exponent 1.5; 42.3 L/s omits the discharge coefficient (Cd ≈ 0.58); 2.47 L/s is a unit slip.
Further reading: USBR Water Measurement Manual
The side slopes of a Cipolletti weir are:
B. 1 horizontal to 4 vertical
Cipolletti chose 1H:4V so that the added flow through the sloping sides offsets the end contractions, giving Q = 1.86 L H^1.5 (SI) with no contraction correction. 1:1 sides make a 90° notch-like trapezoid, and 4H:1V is far too flat.
Further reading: USBR Water Measurement Manual
By Kennedy's theory, what is the critical (non-silting, non-scouring) velocity in a channel 2.0 m deep with critical velocity ratio m = 1.0?
D. 0.86 m/s
V₀ = 0.55 m D^0.64 = 0.55 × 1.0 × 2^0.64 = 0.55 × 1.558 = 0.86 m/s. 1.10 treats the exponent as 1; 0.55 ignores depth; 0.71 uses the wrong exponent.
Further reading: Garg, Irrigation Engineering and Hydraulic Structures
Which of these is an earth-type (non-rigid, soil-based) canal lining?
B. Soil-cement
Soil-cement, compacted earth and bentonite blankets are earth linings. Concrete, brick and asphaltic concrete are hard-surface linings.
Further reading: Garg, Irrigation Engineering and Hydraulic Structures
The culturable command area of a canal is:
B. The gross command area minus unculturable land such as villages, roads, ponds and barren land
CCA excludes land that cannot be cultivated. The area actually irrigated divided by CCA is the intensity of irrigation. The catchment feeds the reservoir and is unrelated to the command.
Further reading: Garg, Irrigation Engineering and Hydraulic Structures
Which set of works forms the core of on-farm development under command area development?
D. Field channels, field drains, land levelling and shaping, and realignment of field boundaries
On-farm development works are below the outlet: field channels, drains, levelling and shaping. Dams, headworks and main canal lining are part of the main system, and insurance is not a CAD work.
Further reading: Government of India CADWM guidelines
A distributary runs for 12 days in each 20-day rotation period. What is its time factor?
C. 0.6
Time factor = days the channel runs / days in the period = 12/20 = 0.6. 1.67 inverts it; 0.4 is the idle fraction; 12 is the number of days, not a ratio.
Further reading: Garg, Irrigation Engineering and Hydraulic Structures
In South Asian canal practice, 'kor watering' refers to:
A. The first watering after sowing (or transplanting), whose depth and period often govern canal capacity
Kor watering is the first irrigation after the crop is sown; it is given within a limited kor period, so it creates a peak demand that fixes canal capacity. The other options are unrelated operations.
Further reading: Garg, Irrigation Engineering and Hydraulic Structures
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