Irrigation Association Certified Agricultural Irrigation Specialist (CAIS) · USA · Irrigation Association
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 Irrigation Association Certified Agricultural Irrigation Specialist spread across the units of Irrigation Engineering (Soil-Water-Plant, Conveyance, Surface Methods). Difficulty: 3 easy, 13 medium, 5 hard.
| Irrigation efficiencies and distribution uniformity | 4 | |
| Irrigation scheduling | 3 | |
| Furrow irrigation | 3 | |
| Soil-water-plant relations: field capacity, wilting point and MAD | 2 | |
| Crop coefficients and crop water requirement | 2 | |
| Water measurement: weirs, Parshall flume and orifices | 2 | |
| Underground pipeline systems | 2 | |
| Basin irrigation | 2 | |
| Effective rainfall | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Where should tensiometers be installed to schedule a deep-rooted row crop?
B. One in the upper root zone to trigger irrigation and one near its bottom to check that water reached it without excess drainage
Most extraction is in the upper root zone, so the trigger sensor goes there; a deeper sensor shows whether the irrigation refilled the lower zone or drained past it. Surface readings fluctuate with evaporation, and sensors below the roots do not see crop use.
Further reading: Irrigation Association scheduling guidance; Michael, Irrigation
A 3-ft Parshall flume reads Ha = 0.50 ft and Hb = 0.40 ft. Which is correct?
C. Submergence is 80 %, above the 70 % free-flow limit for this size, so a submergence correction must be applied
Submergence = Hb/Ha = 0.40/0.50 = 80 %. For 1–8 ft flumes free flow holds up to 70 %, so the flow is submerged and the free-flow rating overstates discharge unless corrected. 125 % inverts the ratio; 20 % is 1 − Hb/Ha.
Further reading: USBR Water Measurement Manual
A buried plastic pipeline 300 m long, 200 mm internal diameter, carries 30 L/s. Using Hazen-Williams with C = 150 (SI: hf = 10.67 L Q^1.852 / (C^1.852 D^4.87)), what is the friction loss?
C. 1.14 m
hf = 10.67 × 300 × 0.03^1.852 / (150^1.852 × 0.2^4.87) = 1.14 m. 10× results from taking L as 3,000 m; 0.039 m uses a 400 mm pipe (diameter doubled); 2.43 m uses C = 100, a value for old rough pipe, not plastic.
Further reading: Hazen-Williams; USDA NRCS NEH Part 623
Catch-can depths along a field (mm) are 10, 12, 8, 14, 6 and 10. What is Christiansen's coefficient of uniformity?
B. 80.0 %
Mean = 10 mm; absolute deviations 0, 2, 2, 4, 4, 0 sum to 12. CU = 100 (1 − 12 / (6 × 10)) = 80.0 %. 60 % is the minimum divided by the mean; −20 % forgets to divide by n; 86.7 % uses the range instead of summed deviations.
Further reading: Christiansen (1942)
Infiltrated depths (mm) at eight equally spaced points are 22, 30, 26, 34, 18, 28, 32 and 30. What is the low-quarter distribution uniformity?
D. 72.7 %
Mean = 220 / 8 = 27.5 mm. The lowest quarter (2 of 8 values) is 18 and 22, mean 20 mm. DU = 20/27.5 = 72.7 %. 65.5 % uses only the minimum; 85.5 % averages the lowest half; 58.8 % divides by the maximum.
Further reading: Irrigation Association; Burt et al. (1997)
An irrigation must apply at least 80 mm to the driest quarter of a field. The system's low-quarter DU is 0.80. What average depth must be infiltrated?
C. 100 mm
Average = required low-quarter depth / DU = 80 / 0.80 = 100 mm. 64 mm multiplies by DU; 80 mm assumes perfect uniformity; 144 mm adds 80 % of 80 to 80.
Further reading: Irrigation Association
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