ASRB NET — Farm Machinery & Power / Land & Water Management Engineering / Agricultural Structures & Process Engineering · India · Agricultural Scientists Recruitment Board (ICAR)
Original practice questions written to the published syllabus · not past papersRain to runoff: measuring precipitation, subtracting losses, estimating runoff and routing floods.
In the exams: GATE AG Section 4 Hydrology (SWCE is the heaviest GATE section, ~16 marks a year 2019–26); ICAR AIEEA-PG Unit VII; ICAR AICE subjects 40 and 43; NCEES PE hydrology; state PSCs
ASRB NET — Land & Water Management Engineering
Hydrology and soil and water conservation at PG depth: similar to the ICAR PhD papers, with emphasis on concepts and standard formulas.
How our questions for ASRB NET spread across the units of Watershed Hydrology. Difficulty: 1 easy, 6 medium, 17 hard.
| S-curve, IUH and synthetic unit hydrographs | 4 | |
| Drought classification | 4 | |
| Infiltration: Horton, Philip and the phi-index | 3 | |
| Frequency analysis, return period and IDF curves | 2 | |
| Runoff estimation: SCS curve number | 2 | |
| Streamflow measurement | 2 | |
| Flood routing: Muskingum and reservoir (Puls) methods | 2 | |
| The hydrologic cycle | 1 | |
| Precipitation measurement and rain-gauge networks | 1 | |
| Missing rainfall data and double-mass analysis | 1 | |
| Interception and evaporation (pan) | 1 | |
| Hydrographs and the unit hydrograph | 1 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
In a humid, forested headwater catchment with deep permeable soils, storm runoff comes mainly from narrow saturated zones beside the stream that expand during the storm and shrink afterwards. This behaviour is best described as:
C. saturation-excess runoff from a variable source area
Where infiltration capacity is high, overland flow arises only where the soil has saturated from below, first near streams; the contributing area varies with wetness (the variable source area concept). Hortonian flow over the whole catchment needs intensity above infiltration capacity everywhere, which deep forest soils rarely allow.
Further reading: Chow, Maidment and Mays, Applied Hydrology
Using Meyer's formula E = C(ew − ea)(1 + u₉/16) with C = 0.36 for a large deep reservoir, estimate daily evaporation when ew = 23.76 mm Hg, ea = 11.88 mm Hg and u₉ = 16 km/h.
B. 8.55 mm/day
E = 0.36 × (23.76 − 11.88) × (1 + 16/16) = 0.36 × 11.88 × 2 = 8.55 mm/day. C = 0.50 is for small shallow waters; omitting the wind term gives 4.28; using ew instead of the difference gives 17.11.
Further reading: Subramanya, Engineering Hydrology
A 5-hour storm has hourly rainfall of 8, 18, 30, 12 and 5 mm. The direct runoff depth is 32 mm. The φ-index is:
B. 9.33 mm/h
Assume the 18, 30 and 12 mm hours exceed φ: 60 − 3φ = 32, so φ = 9.33 mm/h. Check: 8 and 5 are below it and 12 is above, so the assumption holds. 8.20 is total loss divided by duration, which ignores that low-intensity hours lose less than φ; 9.00 assumes four hours contribute, but then 8 < 9.0 fails the check. 10.25 mm/h divides the total loss (73 − 32 = 41 mm) by four hours.
Further reading: Subramanya, Engineering Hydrology
Using Muskingum coefficients C₀ = 0.0323, C₁ = 0.6129 and C₂ = 0.3548, with inflow rising from I₁ = 40 to I₂ = 85 m³/s and outflow O₁ = 38 m³/s, the outflow at the end of the step is:
B. 40.7 m³/s
O₂ = C₀I₂ + C₁I₁ + C₂O₁ = 0.0323×85 + 0.6129×40 + 0.3548×38 = 40.7 m³/s. Swapping I₁ and I₂ gives 66.9; dropping the C₀I₂ term gives 38.0. 62.5 m³/s simply averages the two inflows.
Further reading: Subramanya, Engineering Hydrology
For Muskingum routing with K = 10 h and x = 0.2, the range of routing interval Δt that keeps all three coefficients non-negative is:
B. 4 h ≤ Δt ≤ 16 h
C₀ ≥ 0 requires Δt ≥ 2Kx = 4 h; C₂ ≥ 0 requires Δt ≤ 2K(1 − x) = 16 h. The upper limit is not K itself, a common simplification.
Further reading: Subramanya, Engineering Hydrology
For a district and week, current NDVI is 0.42, and the historical minimum and maximum NDVI for that week are 0.30 and 0.70. The Vegetation Condition Index is:
D. 30%
VCI = (NDVI − NDVImin)/(NDVImax − NDVImin) × 100 = (0.42 − 0.30)/(0.40) × 100 = 30%. 60% divides by the maximum only; 70% measures distance from the maximum instead. 42% simply reads the current NDVI as a percentage.
Further reading: WMO Handbook of Drought Indicators and Indices
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