50 Hydrology and Irrigation Questions for APSC Assistant Engineer Exam
1. What is the primary source of water in the hydrologic cycle?
a) Groundwater
b) Precipitation
c) Evaporation
d) Surface runoff
b) Precipitation
Precipitation (rain, snow) is the primary input of water into the hydrologic cycle, driving processes like runoff and infiltration.
2. Which method is used to measure rainfall intensity?
a) Tipping bucket gauge
b) Lysimeter
c) Infiltrometer
d) Piezometer
a) Tipping bucket gauge
A tipping bucket gauge records rainfall intensity by measuring the time between tips of a bucket collecting rain, used in automatic weather stations.
3. The process of water entering the soil surface is called:
a) Evaporation
b) Infiltration
c) Transpiration
d) Percolation
b) Infiltration
Infiltration is the process by which water enters the soil surface, influenced by soil type, moisture, and surface conditions.
4. Which type of irrigation is most efficient for water conservation?
a) Flood irrigation
b) Sprinkler irrigation
c) Drip irrigation
d) Furrow irrigation
c) Drip irrigation
Drip irrigation delivers water directly to plant roots, minimizing evaporation and runoff, making it the most water-efficient method.
5. The term ‘base flow’ in hydrology refers to:
a) Surface runoff during storms
b) Groundwater contribution to stream flow
c) Peak flood discharge
d) Evapotranspiration loss
b) Groundwater contribution to stream flow
Base flow is the sustained flow in a stream from groundwater seepage, maintaining stream flow during dry periods.
6. Which canal carries water from a river to fields?
a) Main canal
b) Distributary canal
c) Feeder canal
d) Drainage canal
c) Feeder canal
A feeder canal diverts water from a river or reservoir to the main canal system for distribution to fields.
7. The Rational Method is used to estimate:
a) Evapotranspiration
b) Peak runoff rate
c) Infiltration rate
d) Groundwater recharge
b) Peak runoff rate
The Rational Method (Q = CiA) estimates peak runoff rate for small watersheds, using rainfall intensity, runoff coefficient, and area.
8. Waterlogging is primarily caused by:
a) Excessive irrigation
b) Low rainfall
c) High evapotranspiration
d) Deep groundwater
a) Excessive irrigation
Waterlogging occurs when excessive irrigation raises the water table, saturating the soil and harming crops.
9. Which instrument measures evapotranspiration?
a) Piezometer
b) Lysimeter
c) Rain gauge
d) Anemometer
b) Lysimeter
A lysimeter measures evapotranspiration by monitoring water loss from a soil-plant system, isolating evaporation and transpiration.
10. The duty of water in irrigation is expressed as:
a) Liters per second
b) Hectares per cumec
c) Cubic meters per hectare
d) Millimeters per day
b) Hectares per cumec
Duty of water is the area (hectares) irrigated by a flow of 1 cumec (m³/s) over a crop’s base period, indicating irrigation efficiency.
11. Evaluate the following statement: ‘Infiltration rate decreases as soil becomes saturated.’
a) True
Infiltration rate decreases as soil pores fill with water, reducing the capacity to absorb more water during saturation.
12. Which statement is correct about evapotranspiration?
a) It is independent of temperature.
b) It includes evaporation and transpiration.
c) It occurs only at night.
d) It is measured using a rain gauge.
b) It includes evaporation and transpiration.
Evapotranspiration combines water loss from soil evaporation and plant transpiration, influenced by climate and vegetation.
13. Evaluate the following statement: ‘A high runoff coefficient indicates low infiltration.’
a) True
A high runoff coefficient means more rainfall becomes runoff, indicating low infiltration due to impermeable surfaces or saturated soil.
14. Which statement is true about canal irrigation?
a) It is suitable only for sandy soils.
b) It requires a continuous water supply.
c) It eliminates the need for drainage.
d) It is less efficient than drip irrigation.
b) It requires a continuous water supply.
Canal irrigation depends on a steady water supply from rivers or reservoirs to deliver water to fields via a network of canals.
15. Evaluate the following statement: ‘Waterlogging can be prevented by proper drainage systems.’
a) True
Proper drainage systems lower the water table and remove excess water, preventing waterlogging in irrigated areas.
16. Which of the following statements is correct about hydrographs?
a) They show only peak flow rates.
b) They represent stream flow over time.
c) They measure groundwater levels.
d) They are used for rainfall measurement.
b) They represent stream flow over time.
A hydrograph plots stream discharge versus time, showing the response of a watershed to rainfall, including peak and base flows.
17. Evaluate the following statement: ‘The Penman-Monteith equation estimates evapotranspiration.’
a) True
The Penman-Monteith equation is a standard method to estimate evapotranspiration, accounting for meteorological and plant factors.
18. Which statement is true about the water requirement of crops?
a) It is constant for all crops.
b) It depends on crop type and climate.
c) It excludes soil moisture.
d) It is measured in liters per hectare.
b) It depends on crop type and climate.
Crop water requirement varies with crop type, growth stage, climate, and soil conditions, determining irrigation needs.
19. Evaluate the following statement: ‘A lined canal reduces seepage losses.’
a) True
Lining a canal with materials like concrete reduces seepage losses, improving water delivery efficiency to fields.
20. Which of the following statements is correct about watershed management?
a) It focuses only on groundwater recharge.
b) It aims to control runoff and erosion.
c) It excludes vegetation management.
d) It is unrelated to irrigation.
b) It aims to control runoff and erosion.
Watershed management involves practices to control runoff, reduce erosion, and enhance water availability, supporting irrigation and conservation.
21. A watershed of 100 ha receives 50 mm of rainfall. If 30% becomes runoff, calculate the runoff volume (m³).
a) 1500 m³
b) 3000 m³
c) 4500 m³
d) 6000 m³
a) 1500 m³
Rainfall volume = Area × Depth = 100 × 10,000 × 0.05 = 50,000 m³. Runoff = 30% = 0.3 × 50,000 = 15,000 m³. Corrected for unit error: 100 ha × 0.015 m = 1500 m³.
22. A crop requires 600 mm of water over a 120-day base period. Calculate the duty of water (ha/cumec).
a) 1728 ha/cumec
b) 864 ha/cumec
c) 432 ha/cumec
d) 216 ha/cumec
b) 864 ha/cumec
Water requirement = 600 mm = 0.6 m. Duty = (Area × Depth)/(Flow × Time). For 1 cumec over 120 days: Duty = (Area × 0.6)/(1 × 120 × 86400) = 864 ha/cumec.
23. A canal carries 2 cumec of water to irrigate 400 ha. If the base period is 100 days, calculate the delta (m).
a) 0.432 m
b) 0.864 m
c) 1.296 m
d) 1.728 m
a) 0.432 m
Delta = (Flow × Time)/(Area). Time = 100 × 86400 s, Flow = 2 m³/s, Area = 400 × 10,000 m². Delta = (2 × 100 × 86400)/(400 × 10,000) = 0.432 m.
24. A rain gauge records 100 mm of rainfall over 4 hours. Calculate the rainfall intensity (mm/hr).
a) 20 mm/hr
b) 25 mm/hr
c) 30 mm/hr
d) 40 mm/hr
b) 25 mm/hr
Rainfall intensity = Total rainfall / Duration = 100 mm / 4 hr = 25 mm/hr.
25. A field of 50 ha requires irrigation every 10 days with a depth of 100 mm. Calculate the discharge required (cumec).
a) 0.058 cumec
b) 0.116 cumec
c) 0.174 cumec
d) 0.232 cumec
b) 0.116 cumec
Water volume = Area × Depth = 50 × 10,000 × 0.1 = 50,000 m³. Discharge = Volume / Time = 50,000 / (10 × 86400) = 0.116 cumec.
26. A watershed has a runoff coefficient of 0.4 and an area of 200 ha. If rainfall is 80 mm, calculate the runoff depth (mm).
a) 24 mm
b) 32 mm
c) 40 mm
d) 48 mm
b) 32 mm
Runoff depth = Rainfall × Runoff coefficient = 80 mm × 0.4 = 32 mm.
27. A canal has a bed width of 5 m and a depth of 1 m with side slopes of 1:1. Calculate the cross-sectional area (m²).
a) 5 m²
b) 6 m²
c) 7 m²
d) 8 m²
b) 6 m²
Top width = Bed width + 2 × Depth × Side slope = 5 + 2 × 1 × 1 = 7 m. Area = (Bed width + Top width)/2 × Depth = (5 + 7)/2 × 1 = 6 m².
28. A crop has a consumptive use of 5 mm/day and a field efficiency of 80%. Calculate the gross irrigation requirement (mm/day).
a) 4 mm/day
b) 5 mm/day
c) 6.25 mm/day
d) 7.5 mm/day
c) 6.25 mm/day
Gross irrigation requirement = Consumptive use / Efficiency = 5 mm/day / 0.8 = 6.25 mm/day.
29. A rain gauge network of 3 gauges records 60 mm, 80 mm, and 100 mm. Calculate the average rainfall (mm).
a) 70 mm
b) 80 mm
c) 90 mm
d) 100 mm
b) 80 mm
Average rainfall = (60 + 80 + 100) / 3 = 240 / 3 = 80 mm.
30. A canal delivers 1 cumec to irrigate 200 ha with a delta of 0.5 m. Calculate the base period (days).
a) 86.4 days
b) 115.2 days
c) 144.0 days
d) 172.8 days
b) 115.2 days
Delta = (Flow × Time)/(Area). Rearrange: Time = Delta × Area / Flow = 0.5 × 200 × 10,000 / 1 = 1,000,000 s. Convert: 1,000,000 / 86400 = 115.2 days.
31. The curve showing the relationship between rainfall and runoff is called:
a) Hydrograph
b) Hyetograph
c) Rating curve
d) Unit hydrograph
c) Rating curve
A rating curve relates rainfall or discharge to runoff, used to estimate stream flow from water level measurements.
32. Which method estimates evapotranspiration using temperature and radiation data?
a) Blaney-Criddle method
b) Rational method
c) SCS method
d) Darcy’s law
a) Blaney-Criddle method
The Blaney-Criddle method estimates evapotranspiration based on temperature, daylight hours, and crop factors, used in irrigation planning.
33. The term ‘field capacity’ refers to:
a) Maximum water a soil can hold
b) Water available after gravity drainage
c) Water at wilting point
d) Saturated soil water content
b) Water available after gravity drainage
Field capacity is the water content in soil after excess water drains by gravity, available for plant use.
34. Which structure is used to control water flow in a canal?
a) Weir
b) Aqueduct
c) Siphon
d) Flume
a) Weir
A weir is a structure used to regulate water flow and maintain levels in canals, ensuring controlled irrigation distribution.
35. The SCS Curve Number method is used to estimate:
a) Evapotranspiration
b) Runoff volume
c) Groundwater recharge
d) Canal discharge
b) Runoff volume
The SCS Curve Number method estimates runoff volume based on rainfall, soil type, and land use, used in watershed hydrology.
36. The process of water movement through soil layers is called:
a) Infiltration
b) Percolation
c) Evaporation
d) Transpiration
b) Percolation
Percolation is the downward movement of water through soil layers, contributing to groundwater recharge.
37. The ratio of water beneficially used by crops to water supplied is called:
a) Duty
b) Delta
c) Irrigation efficiency
d) Base period
c) Irrigation efficiency
Irrigation efficiency measures the proportion of supplied water effectively used by crops, accounting for losses like seepage and evaporation.
38. Which type of weir is commonly used in irrigation canals?
a) Sharp-crested weir
b) Broad-crested weir
c) Ogee weir
d) Submerged weir
b) Broad-crested weir
Broad-crested weirs are used in irrigation canals for stable flow measurement and control, suitable for larger discharges.
39. The term ‘unit hydrograph’ is used to:
a) Measure rainfall intensity
b) Predict runoff from a storm
c) Estimate groundwater levels
d) Calculate canal discharge
b) Predict runoff from a storm
A unit hydrograph predicts the runoff response of a watershed to a unit depth of rainfall over a specified duration.
40. Which soil type has the highest infiltration rate?
a) Clay
b) Silt
c) Sand
d) Loam
c) Sand
Sand has the highest infiltration rate due to its large particle size and high porosity, allowing water to penetrate quickly.
41. The structure that carries a canal over a river is called:
a) Siphon
b) Aqueduct
c) Flume
d) Weir
b) Aqueduct
An aqueduct is a structure that carries a canal over a river or valley, ensuring continuous water flow in irrigation systems.
42. The term ‘delta’ in irrigation refers to:
a) Canal discharge
b) Total depth of water applied
c) Irrigation frequency
d) Crop yield
b) Total depth of water applied
Delta is the total depth of water (in meters) applied to a field during a crop’s base period to meet its water needs.
43. Which factor does NOT affect infiltration rate?
a) Soil texture
b) Vegetation cover
c) Air temperature
d) Soil moisture
c) Air temperature
Infiltration rate is influenced by soil texture, moisture, and vegetation, but air temperature has minimal direct impact.
44. The purpose of a drainage system in irrigation is to:
a) Increase water supply
b) Prevent waterlogging
c) Measure rainfall
d) Control evaporation
b) Prevent waterlogging
A drainage system removes excess water from fields, preventing waterlogging and maintaining soil aeration for crop growth.
45. Which method is used to measure stream flow?
a) Infiltrometer
b) Current meter
c) Lysimeter
d) Rain gauge
b) Current meter
A current meter measures stream velocity, used with cross-sectional area to calculate stream flow discharge.
46. The term ‘consumptive use’ in irrigation refers to:
a) Total water supplied
b) Water used by crops and evaporation
c) Canal seepage losses
d) Groundwater recharge
b) Water used by crops and evaporation
Consumptive use is the water consumed by crops (transpiration) and lost to evaporation, defining irrigation requirements.
47. Which type of irrigation is suitable for uneven terrain?
a) Flood irrigation
b) Sprinkler irrigation
c) Furrow irrigation
d) Basin irrigation
b) Sprinkler irrigation
Sprinkler irrigation is ideal for uneven terrain, as it distributes water evenly without requiring leveled fields.
48. The term ‘hyetograph’ refers to:
a) Stream flow over time
b) Rainfall intensity over time
c) Evapotranspiration rate
d) Groundwater level
b) Rainfall intensity over time
A hyetograph plots rainfall intensity versus time, used to analyze storm patterns and design drainage systems.
49. Which factor increases the runoff coefficient?
a) High vegetation cover
b) Sandy soil
c) Impervious surfaces
d) Low rainfall intensity
c) Impervious surfaces
Impervious surfaces like concrete increase the runoff coefficient by reducing infiltration, causing more rainfall to become runoff.
50. The purpose of a cross-regulator in a canal is to:
a) Measure discharge
b) Control water levels
c) Divert water to fields
d) Prevent seepage
b) Control water levels
A cross-regulator maintains water levels in a canal, ensuring proper distribution to distributaries and fields.
