GATE — Environmental Science and Engineering (ES) · India · IITs and IISc on rotation (2026: IIT Guwahati)
Original practice questions written to the published syllabus · not past papersThe water cycle, surface and groundwater resources and the hydraulics that GATE ES Section 4 examines. Agricultural engineering already teaches watershed hydrology, groundwater and canal hydraulics to design level (subjects watershed-hydrology and groundwater-wells-pumps); this subject covers what an environmental scientist needs and the environmental framing: water balance, threats to water resources and channel and pipe flow basics.
In the exams: GATE ES Section 4 (a large numerical section); ICAR AIEEA-PG Water Science & Technology group; ICAR AICE subject 71 Unit 1 (watersheds)
GATE -- Environmental Science and Engineering (Section 4)
A heavily numerical section: water balance, SCS-CN and rational method, unit hydrograph convolution, Muskingum coefficients, Darcy and seepage velocity, Thiem and Dupuit wells, hydrostatic forces, Bernoulli and continuity, Darcy-Weisbach, Manning, critical depth, hydraulic jump, venturi and weirs. Numerical-answer-type items demand exact unit handling.
How our questions for GATE spread across the units of Hydrology & Water Resources for Environmental Scientists. Difficulty: 16 easy, 14 medium, 7 hard.
| Continuity, momentum and energy equations; pipe flow and pipe networks | 4 | |
| Open-channel flow: specific energy, critical flow, hydraulic jump | 4 | |
| The hydrological cycle and water balance | 3 | |
| Precipitation, infiltration, evapotranspiration and runoff | 3 | |
| Hydrographs and the unit hydrograph | 3 | |
| Stage-discharge relationships and reservoir capacity | 3 | |
| Reservoir and channel routing | 3 | |
| Aquifers: confined, unconfined, porosity, transmissivity, storage | 3 | |
| Darcy's law and steady-state well hydraulics | 3 | |
| Fluid properties, hydrostatics, buoyancy | 3 | |
| Flow measurement in pipes and channels | 3 | |
| Global water resources: distribution, quality and threats | 2 |
Choose an answer, then open the working. Each explanation says why the right answer is right and why the others are not.
Where is most of the world's fresh water stored?
C. Ice and snow
About 69% is ice and snow, about 30% groundwater, about 1% surface and other water.
A 3-hour unit hydrograph (for 1 cm) has ordinates [0, 20, 50, 30, 10, 0] m3/s at 3-hour intervals. Effective rainfall is 2.0 cm in the first 3 hours and 1.0 cm in the next 3 hours. What is the peak of the direct runoff hydrograph?
B. 120 m3/s
Convolution: DRH = 2 x UH(t) + 1 x UH(t - 3 h); ordinates [0.0, 40.0, 120.0, 110.0, 50.0, 10.0, 0.0]; peak 120. Multiplying the UH peak by 3 cm assumes both blocks peak together; 110 is the next ordinate, not the peak.
The storage in a reservoir below the lowest outlet is called:
B. Dead storage
Dead storage is unusable by gravity and partly reserved for sediment.
Monthly inflows to a reservoir site are [10, 2, 1, 8, 12, 3, 1, 9] (million m3) and the demand is a constant 6 million m3/month. Using the sequent peak (cumulative deficit) method, what storage is required?
B. 9 million m3
Running deficit K_t = max(0, K_t-1 + demand - inflow): the maximum is 9. Summing all monthly shortfalls (17) ignores refilling between dry spells.
Using C0 = 0.048, C1 = 0.429, C2 = 0.524, inflows I1 = 30 and I2 = 50 m3/s and outflow O1 = 25 m3/s, what is O2?
D. 28.3 m3/s
O2 = C0 I2 + C1 I1 + C2 O1 = 2.38 + 12.86 + 13.10 = 28.3. Swapping I1 and I2 gives 36.0.
A well pumps 1,728 m3/day from a confined aquifer. Steady drawdowns are 3.0 m at 10 m and 1.0 m at 100 m. Using Thiem, what is the transmissivity?
D. 317 m2/day
T = Q ln(r2/r1) / [2 pi (s1 - s2)] = 1,728 x 2.303 / (2 pi x 2) = 317. Using log10 gives 138.
Water flows at 0.05 m3/s through a pipe of diameter 0.1 m. What is the mean velocity?
D. 6.37 m/s
V = Q / A = 0.05 / (pi x 0.05^2) = 6.37. Using d instead of d/2 in the area gives 1.59.
A pump delivers 0.1 m3/s against a head of 30 m with efficiency 0.75. What power does it require?
A. 39.2 kW
P = rho g Q H / eta = 1,000 x 9.81 x 0.1 x 30 / 0.75 = 39.2 kW.
Minimum specific energy in a rectangular channel equals:
A. 1.5 times critical depth
E_min = 1.5 y_c. At this minimum the flow is critical, with Froude number 1.
A venturi meter (inlet 0.3 m, throat 0.15 m diameter, Cd = 0.98) shows a differential head of 0.5 m of water. What is the discharge?
C. 0.0560 m3/s
Q = Cd A1 A2 sqrt(2gh)/sqrt(A1^2 - A2^2) = 0.0560. Ignoring the approach-velocity term or using Cd = 0.6 gives the others.
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