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Past Questions
What are the primary components of a sub-surface drainage system?
A)
Open ditches and barriers
B)
Perforated pipes and drains
C)
Wind barriers and ridges
D)
Artificial reservoirs
Sub-surface drainage (also known as underground drainage) is designed to remove excess water from the root zone of crops to prevent waterlogging and salinity. The primary components of such a system are perforated pipes (laterals and collectors) buried at a specific depth. These pipes allow water to enter through the perforations and transport it via gravity to a main drain or outlet.
Analysis of other options:
- Option (a): Open ditches are components of surface drainage, not sub-surface drainage.
- Option (c): Wind barriers and ridges are used for erosion control and water harvesting/management, not for removing sub-surface excess water.
- Option (d): Artificial reservoirs are used for water storage (irrigation), which is the opposite function of a drainage system.
The main source of irrigation in India is-
A)
Wells
B)
Canals
C)
Rainwater
D)
Lakes
In India, groundwater irrigation (which includes wells and tube wells) is the primary source of irrigation. According to data from the Ministry of Agriculture and Farmers Welfare and various government reports, more than 60% of the total irrigated area in India is covered by groundwater sources.
1. Wells/Tube wells (Option a): These are the most dominant source due to their accessibility and the ability of farmers to control the timing and quantity of water application.
2. Canals (Option b): While significant, especially in Northern India (Punjab, Haryana), canal irrigation covers a smaller percentage of the total irrigated area compared to wells.
3. Rainwater (Option c): Rainwater is the basis for 'rain-fed' agriculture, but by definition, 'irrigation' refers to the artificial application of water to land. Therefore, rainwater is not considered a source of irrigation, but rather a natural source of moisture.
4. Lakes (Option d): Lakes are not a primary or widespread source of systematic irrigation in India.
Which of the following is NOT a type of irrigation?
A)
Drip irrigation
B)
Sprinkler irrigation
C)
Aquifer irrigation
D)
Surface irrigation
Irrigation is the artificial application of water to soil for the purpose of crop production. The options provided are analyzed as follows:
1. **Surface Irrigation (Option d):** This is the most common method where water is applied across the land surface by gravity (e.g., furrow, basin, or border irrigation).
2. **Sprinkler Irrigation (Option b):** A method of applying water in a spray similar to rainfall, using a system of pipes and nozzles.
3. **Drip Irrigation (Option a):** Also known as trickle irrigation, this method delivers water slowly and precisely to the root zone of plants through a network of valves and emitters.
4. **Aquifer Irrigation (Option c):** An aquifer is a geological formation (rock or sediment) that stores and transmits groundwater. While water is *extracted* from an aquifer to be used for irrigation, 'Aquifer irrigation' is not a recognized technical category or method of applying water to crops. The process of using groundwater is generally categorized under the delivery method (e.g., using a pump to feed a drip or sprinkler system).
Therefore, 'Aquifer irrigation' is not a type of irrigation method.
Which type of traversing is best suited for an area with multiple obstacles?
A)
Open traverse
B)
Closed traverse
C)
Radial traverse
D)
Triangulation
In surveying, a traverse is a series of connected lines whose lengths and directions are measured.
1. **Closed Traverse (Option b):** A closed traverse returns to its starting point or connects to a known point. This is the best choice for areas with multiple obstacles because the surveyor can 'navigate around' the obstacles by adjusting the path of the traverse. More importantly, closed traverses provide a mechanism for checking accuracy (closing error), which is critical when the path must be deviated due to obstacles.
2. **Open Traverse (Option a):** An open traverse does not return to the start or close on a known point. It is typically used for linear projects like roads or pipelines. It provides no internal check for errors, making it unreliable for complex areas with obstacles where deviations are frequent.
3. **Radial Traverse (Option c):** In a radial traverse, all lines are run from a single central point. This is only possible if the central point has a clear line of sight to all other points. If there are multiple obstacles, the line of sight is blocked, making this method impossible to implement.
4. **Triangulation (Option d):** Triangulation is a method of determining coordinates based on angles of triangles. While highly accurate for large areas, it requires clear inter-visibility between stations to form triangles. Obstacles significantly hinder the ability to establish these necessary lines of sight.
Which of the following is a disadvantage of flood irrigation?
A)
High efficiency
B)
High water loss due to evaporation
C)
Uniform water distribution
D)
Cost-effectiveness
Flood irrigation (also known as surface irrigation) involves pumping or diverting water onto a field and allowing it to flow over the soil surface.
1. Why option (b) is correct: Because water is spread over a large surface area and remains exposed to the atmosphere for extended periods, a significant volume of water is lost to evaporation and deep percolation. This makes it one of the least water-efficient irrigation methods.
2. Why other options are incorrect:
- Option (a) 'High efficiency': Flood irrigation is characterized by low efficiency (often below 50%) compared to drip or sprinkler irrigation.
- Option (c) 'Uniform water distribution': Flood irrigation often results in non-uniform distribution, where the head of the field (where water enters) is over-saturated while the tail end may be under-watered.
- Option (d) 'Cost-effectiveness': While flood irrigation is often low-cost in terms of initial infrastructure (no expensive pipes or nozzles), 'cost-effectiveness' is generally considered an advantage, not a disadvantage.
Which of the following is NOT an advantage of sprinkler irrigation?
A)
Suitable for undulating terrain
B)
Efficient water distribution
C)
Reduces soil erosion
D)
Lowinitial investment cost
Sprinkler irrigation is a pressurized irrigation system. Let's evaluate the options based on engineering principles:
1. **Suitable for undulating terrain (Option a):** This is an ADVANTAGE. Unlike surface irrigation (which requires precise land leveling), sprinklers can be used on slopes and uneven ground because water is delivered under pressure.
2. **Efficient water distribution (Option b):** This is an ADVANTAGE. Sprinklers allow for precise control over the amount of water applied, reducing waste compared to flood irrigation.
3. **Reduces soil erosion (Option c):** This is generally an ADVANTAGE. Because water is applied in small droplets (simulating rain) rather than in heavy flows or floods, it prevents the surface runoff that typically causes soil erosion on slopes.
4. **Low initial investment cost (Option d):** This is NOT an advantage; it is a DISADVANTAGE. Sprinkler systems require a significant initial capital investment for pumps, piping, nozzles, and control valves, making them much more expensive to install than traditional surface irrigation methods.
Therefore, option (d) is the correct answer as it is a drawback, not an advantage.
The process of artificially supplying water to land for agricultural purposes is called-
A)
Drainage
B)
Irrigation
C)
Evaporation
D)
Infiltration
Step-by-step reasoning:
1. Analysis of the definition: The question asks for the term describing the artificial application of water to land for agriculture.
2. Evaluating Option (b) Irrigation: By definition, irrigation is the artificial process of applying controlled amounts of water to land to assist in the production of crops, especially in areas where rainfall is insufficient.
3. Evaluating Option (a) Drainage: Drainage is the opposite of irrigation; it is the natural or artificial removal of excess surface and sub-surface water from the land.
4. Evaluating Option (c) Evaporation: Evaporation is a physical process where liquid water changes into water vapor due to heat; it is a loss of water from the soil/plant system, not a supply method.
5. Evaluating Option (d) Infiltration: Infiltration is the process by which water on the ground surface enters the soil. While it happens during irrigation, it describes the movement of water into the soil, not the act of supplying it to the land.
Therefore, 'Irrigation' is the only correct term for the artificial supply of water for agricultural purposes.
A trapezoidal canal has a bottom width of 4 m, depth of 2 m, and side slope of 1:1. What is the top width?
A)
6m
B)
8m
C)
10m
D)
12m
To find the top width of a trapezoidal canal, we use the geometry of the cross-section.
1. **Given Data:**
- Bottom width (b) = 4 m
- Depth (d) = 2 m
- Side slope (z) = 1:1 (This means for every 1 unit of vertical rise, there is 1 unit of horizontal run. Therefore, z = 1).
2. **Formula for Top Width (T):**
The top width of a trapezoidal channel is calculated as:
T = b + 2 * (z * d)
3. **Calculation:**
T = 4 + 2 * (1 * 2)
T = 4 + 2 * (2)
T = 4 + 4
T = 8 m
4. **Analysis of Options:**
- Option (a) 6m: Incorrect. This would occur if the side slope was 0.5:1.
- Option (b) 8m: Correct. Matches the calculated value.
- Option (c) 10m: Incorrect. This would occur if the side slope was 1.5:1.
- Option (d) 12m: Incorrect. This would occur if the side slope was 2:1.
Using Manning’s formula, determine the velocity of flow in a canal with: Hydraulic radius (R) = 1.5 m, Slope (S) = 0.0003, Manning’s coefficient (n) = 0.025
A)
0.908 m/s
B)
0.851 m/s
C)
0.932 m/s
D)
0.899 m/s
To determine the velocity of flow in the canal, we use Manning's formula for open channel flow:
Formula: V = (1/n) * R^(2/3) * S^(1/2)
Given values:
- Manning's coefficient (n) = 0.025
- Hydraulic radius (R) = 1.5 m
- Slope (S) = 0.0003
Step-by-step Calculation:
1. Calculate R^(2/3):
R^(2/3) = (1.5)^(2/3) ≈ 1.31037
2. Calculate S^(1/2):
S^(1/2) = √(0.0003) ≈ 0.01732
3. Substitute the values into the formula:
V = (1 / 0.025) * 1.31037 * 0.01732
V = 40 * 1.31037 * 0.01732
V = 52.4148 * 0.01732
V ≈ 0.9078 m/s
Rounding to three decimal places, we get V = 0.908 m/s.
Comparing this result with the given options:
- Option (a) 0.908 m/s matches our calculation.
- Options (b), (c), and (d) are incorrect as they do not align with the mathematical result of the Manning's formula for the provided parameters.
A canal has a bed slope of 1 in 5000, what is the value of S?
A)
0.0001
B)
0.0002
C)
0.0005
D)
0.0010
In hydraulics and civil engineering, the bed slope (S) of a canal is defined as the ratio of the vertical drop (fall) to the horizontal distance.
Given:
Bed slope = 1 in 5000
Calculation:
S = Vertical Drop / Horizontal Distance
S = 1 / 5000
S = 0.0002
Verification of options:
- Option a: 0.0001 corresponds to a slope of 1 in 10,000.
- Option b: 0.0002 corresponds to a slope of 1 in 5,000. (Correct)
- Option c: 0.0005 corresponds to a slope of 1 in 2,000.
- Option d: 0.0010 corresponds to a slope of 1 in 1,000.
If the velocity ratio V/Vc is less than 1 in a canal, what does it indicate?
A)
The canal will experience scouring
B)
The canal will experience silting
C)
The canal is in equilibrium
D)
The canal will have constant velocity
In canal engineering, the stability of the bed is determined by comparing the actual velocity (V) of the water with the critical velocity (Vc), also known as the non-silting or non-scouring velocity.
1. **Critical Velocity (Vc):** This is the velocity at which the sediment transported by the water is neither deposited nor eroded from the bed. This state is known as the 'regime' or 'equilibrium' condition.
2. **Velocity Ratio (V/Vc) < 1:** When the actual velocity (V) is less than the critical velocity (Vc), the water does not have enough kinetic energy to keep the sediment particles in suspension. Consequently, the particles settle down on the bed of the canal, leading to the accumulation of sediment. This process is called **silting**.
3. **Velocity Ratio (V/Vc) > 1:** When the actual velocity is greater than the critical velocity, the water has excess energy that removes particles from the bed, leading to erosion. This process is called **scouring**.
4. **Velocity Ratio (V/Vc) = 1:** This represents the equilibrium condition where no silting or scouring occurs.
Therefore, since the question specifies V/Vc < 1, the canal will experience silting.
What is the typical range of Manning’s roughness coefficient for concrete-lined canals?
A)
0.002 — 0.005
B)
0.006 — 0.009
C)
0.012 -—0.017
D)
0.02 — 0.03
Manning's roughness coefficient (n) is an empirical value used in the Manning formula to calculate the velocity of water in open channels. The value of 'n' depends on the surface roughness of the channel lining.
1. **Concrete-lined canals**: Finished concrete typically has a Manning's n value ranging from 0.011 to 0.017. For standard concrete-lined irrigation canals, the value is generally accepted in the range of 0.012 to 0.017.
2. **Analysis of other options**:
- **Options (a) and (b)**: Values like 0.002 to 0.009 are extremely low and are typically associated with very smooth surfaces like glass or polished plastics, which are not used for lining large-scale irrigation canals.
- **Option (d)**: Values between 0.02 and 0.03 are typical for earth channels (smooth) or rubble masonry, which are rougher than finished concrete.
Therefore, option (c) represents the standard engineering range for concrete-lined channels.
What is the primary purpose of irrigation in agriculture?
A)
Increase land value
B)
Prevent soil erosion
C)
Ensure adequate moisture for crops
D)
Reduce temperature
Irrigation is defined as the artificial application of water to the soil or land to assist in the production of crops. The primary objective is to supplement rainfall to ensure that plants receive the necessary amount of moisture for growth, especially during dry seasons or in arid regions.
Analysis of other options:
- (a) Increase land value: While productive irrigated land may increase in value, this is an economic byproduct, not the primary agricultural purpose.
- (b) Prevent soil erosion: Improper irrigation (like over-watering or flooding) can actually cause soil erosion. Soil conservation techniques, not irrigation, are used to prevent erosion.
- (d) Reduce temperature: While water can have a cooling effect on the microclimate, the fundamental goal of irrigation is hydration and nutrient transport for the plant, not temperature regulation.
Which of the following is NOT a preventive measure for waterlogging?
A)
Using well-planned irrigation techniques
B)
Installing drainage systems
C)
Growing water-demanding crops in all seasons
D)
Using raised beds for planting
Waterlogging occurs when the soil becomes saturated with water, displacing air from the soil pores and hindering root respiration. To prevent this, measures must focus on controlling the amount of water entering the soil or facilitating its removal.
- Option (a) 'Using well-planned irrigation techniques' (such as drip or sprinkler irrigation) prevents waterlogging by applying only the required amount of water, avoiding over-irrigation.
- Option (b) 'Installing drainage systems' (such as surface or subsurface drains) is a primary preventive and corrective measure to remove excess water from the root zone.
- Option (d) 'Using raised beds for planting' helps prevent waterlogging by elevating the root zone above the saturated soil level, allowing for better aeration.
- Option (c) 'Growing water-demanding crops in all seasons' is NOT a preventive measure. While water-demanding crops (like rice) can tolerate waterlogging, planting them in all seasons does not prevent the soil from becoming waterlogged; in fact, if the soil is naturally prone to waterlogging or if irrigation is excessive, it does not solve the underlying drainage problem and may lead to soil degradation or salinity issues in the long run.
What is the primary advantage of using lined canals over unlined canals?
A)
Increased seepage losses
B)
Reduced seepage losses and increased efficiency
C)
Easier maintenance of canal embankments
D)
Reduced flow velocity
In canal engineering, lining refers to providing an impermeable layer (such as concrete, bricks, or plastic membranes) on the wetted perimeter of the canal.
1. **Seepage Control**: The primary purpose of lining is to prevent water from percolating into the ground (seepage), which is a major source of water loss in unlined canals. This ensures that more water reaches the intended command area.
2. **Increased Efficiency**: By reducing seepage and providing a smoother surface (lower Manning's roughness coefficient), the flow velocity increases. This allows for a smaller cross-sectional area to carry the same discharge, reducing land acquisition costs and increasing overall conveyance efficiency.
Analysis of other options:
- Option (a) is incorrect because lining *decreases* seepage losses, not increases them.
- Option (c) is incorrect because while lining helps prevent erosion, the primary 'advantage' is hydraulic efficiency and water conservation, not necessarily the ease of embankment maintenance.
- Option (d) is incorrect because lining reduces friction, which actually *increases* flow velocity compared to the rougher surface of an unlined canal.
Which factor is most important when designing a drainage system layout?
A)
Soil type and permeability
B)
Color of the soil
C)
Plant height in the previous season
D)
The amount of fertilizers used
In agricultural drainage design, the primary goal is to remove excess water from the root zone to prevent waterlogging and salinity. The efficiency of water movement toward the drainage pipes or ditches is governed by the hydraulic conductivity of the soil, which is directly determined by the soil type (e.g., sandy, loamy, or clayey) and its permeability. Engineers use these factors to determine the spacing between drains and the depth of the system.
Why other options are incorrect:
- b. Color of the soil: While soil color can indicate drainage conditions (e.g., grey colors indicating anaerobic conditions), it is a symptom/indicator, not a design parameter used to calculate layout specifications.
- c. Plant height in the previous season: This is a biological outcome and does not influence the physical engineering requirements of the drainage infrastructure.
- d. The amount of fertilizers used: Fertilizer application is a nutrient management practice; it does not dictate the physical layout or hydraulic capacity of a drainage system.
Using Chezy’s formula, V = C √(RS). If C=50, R=1.8 m, and S=0.0005, find velocity V.
A)
2.5m/s
B)
3.0m/s
C)
2.68 m/s
D)
1.5 m/s
Option C is correct: 2.68 m/s.
The discharge (Q) in a rectangular channel is: Width of channel (b) = 3 m, Depth of flow (h) = 1.2 m, Velocity (V)=1.5 m/s
A)
4.9 m3/s
B)
5.4 m/s
C)
5.6m*/s
D)
5.1 m*/s
To find the discharge (Q) in a rectangular channel, we use the continuity equation: Q = A × V, where 'A' is the cross-sectional area of the flow and 'V' is the average velocity.
Step 1: Calculate the cross-sectional area (A) of the rectangular channel.
Area (A) = Width (b) × Depth of flow (h)
A = 3 m × 1.2 m = 3.6 m²
Step 2: Calculate the discharge (Q).
Q = A × V
Q = 3.6 m² × 1.5 m/s = 5.4 m³/s
Note on Options: While the correct numerical value is 5.4, the unit provided in option (b) is written as 'm/s' (velocity unit) instead of 'm³/s' (discharge unit). However, based on the calculation, 5.4 is the only mathematically correct value. Options a, c, and d are numerically incorrect. Therefore, option (b) is the intended correct answer despite the typographical error in the unit.
Which of the following best describes the primary function of a theodolite in surveying?
A)
Measuring horizontal and vertical angles with high precision
B)
Determining elevations and contours of land
C)
Measuring distances directly between two points
D)
Capturing digital survey data with automated processing
A theodolite is a precision instrument used in surveying primarily for the measurement of angles in both the horizontal and vertical planes.
1. Why Option (a) is correct: The fundamental design of a theodolite consists of a telescope mounted on two axes (horizontal and vertical), allowing the surveyor to sight targets and read the precise angular difference between them using graduated circles. This makes it the primary tool for establishing directions, calculating bearings, and determining vertical angles for trigonometric leveling.
2. Why Option (b) is incorrect: Determining elevations and contours is the primary function of a Level (e.g., Dumpy level or Auto level). While a theodolite can be used for trigonometric leveling, it is not its primary function compared to a level.
3. Why Option (c) is incorrect: Measuring distances directly is the function of a tape, chain, or Electronic Distance Measurement (EDM) device. A standard theodolite measures angles, not linear distances (though a 'Total Station' combines a theodolite with an EDM).
4. Why Option (d) is incorrect: Capturing digital survey data with automated processing describes a Total Station or GPS/GNSS receiver. A traditional theodolite is an optical instrument; while digital theodolites exist, the 'primary function' remains angle measurement, not the overall data processing workflow.
Which method is NOT a technique of contouring?
A)
Direct method
B)
Indirect method
C)
Compass method
D)
Grid method
Contouring is the process of determining the layout of a surface by joining points of equal elevation. There are two primary methods of contouring:
1. Direct Method: In this method, the points on the contour line are located directly in the field using a level and a staff. It is highly accurate but very time-consuming.
2. Indirect Method: In this method, a grid or a series of cross-sections are established, and elevations are taken at specific points. The contour lines are then interpolated between these points in the office. Common techniques under the indirect method include:
- Grid method (or Square method)
- Cross-section method (or Radial line method),
- Tacheometric method.
Option (c) 'Compass method' is used for measuring directions (bearings) and plotting the horizontal plan of an area (traversing), but it cannot measure vertical elevations or be used as a technique to generate contour lines. Therefore, it is NOT a technique of contouring.
What is sub-surface drainage?
A)
A system that removes excess water from below the root zone
B)
A method to increase irrigation water
C)
A method to reduce fertilizer application
D)
A way to improve plant growth by adding chemicals
Sub-surface drainage refers to the removal of excess water from the soil profile (specifically from the root zone and below) to maintain an optimal balance of air and water for plant growth. This is typically achieved using perforated pipes, tiles, or gravel drains buried underground.
Analysis of options:
- Option (a) is correct because the primary purpose of sub-surface drainage is to lower the water table and remove saturated water from below the surface to prevent waterlogging.
- Option (b) is incorrect because drainage is the process of removing water, whereas irrigation is the process of adding water.
- Option (c) is incorrect because while drainage can improve nutrient uptake efficiency, its primary definition is not the reduction of fertilizer application.
- Option (d) is incorrect because drainage is a physical/hydraulic process of water removal, not a chemical additive process.
What is waterlogging in agricultural fields?
A)
Condition where soil lacks organic matter
B)
Condition where soil contains excessive water, reducing air availability
C)
A method of irrigation
D)
Process of adding fertilizers to soil
Waterlogging occurs when the soil becomes saturated with water, filling the pore spaces (macropores) that would normally contain air. This leads to anaerobic conditions (lack of oxygen), which inhibits root respiration and can lead to the death of most terrestrial crops.
Analysis of options:
- Option (a) refers to soil infertility or poor soil health, not waterlogging.
- Option (b) is the correct technical definition of waterlogging in the context of agricultural drainage.
- Option (c) is incorrect; while some irrigation methods (like flood irrigation) can lead to waterlogging if drainage is poor, waterlogging itself is a problematic condition, not a method.
- Option (d) describes fertilization, which is a nutrient management process.
How does a total station improve accuracy in surveying compared to a theodolite?
A)
It reduces the need for manual calculations
B)
It can measure underground features
C)
It works without needing a reference point
D)
It automatically adjusts for atmospheric conditions
A Total Station is an electronic/optical instrument that integrates an Electronic Distance Meter (EDM), an electronic theodolite, and an onboard microprocessor.
1. Why Option (a) is correct: In traditional theodolite surveying, the surveyor must manually read angles and measure distances (using a tape or chain), and then perform trigonometric calculations (like sine and cosine rules) to determine the coordinates (X, Y, Z) of a point. A Total Station performs these calculations automatically and instantaneously using its internal microprocessor, which significantly reduces human error associated with manual data recording and calculation, thereby improving the overall accuracy and efficiency of the survey.
2. Why Option (b) is incorrect: Total Stations use electromagnetic waves (infrared or laser) which cannot penetrate the ground; they cannot measure underground features.
3. Why Option (c) is incorrect: Like a theodolite, a Total Station requires a known reference point (station) and a known orientation (backsight) to establish a coordinate system.
4. Why Option (d) is incorrect: While some high-end Total Stations allow the user to input atmospheric data (temperature and pressure) to correct the EDM measurement, they do not 'automatically' adjust for these conditions without input or specialized sensors, and this is a refinement of distance measurement rather than the primary fundamental improvement in accuracy over a theodolite.
Why are clayey soils more prone to waterlogging compared to sandy soils?
A)
Clayey soils have larger pore spaces
B)
Clayey soils allow faster infiltration
C)
Clayey soils have lower permeability
D)
Clayey soils absorb more oxygen
Waterlogging occurs when the soil becomes saturated and water cannot drain away effectively. The ability of soil to transmit water is known as hydraulic conductivity or permeability.
1. **Clayey Soils**: These soils consist of very fine particles with small, interconnected micropores. While they have high total porosity, the small size of the pores creates high resistance to water flow, resulting in low permeability. Consequently, water accumulates in the root zone, leading to waterlogging.
2. **Sandy Soils**: These consist of larger particles with large macropores, allowing water to move quickly through the profile via gravity (high permeability), which prevents waterlogging.
Evaluating the options:
- **Option a** is incorrect because clayey soils have smaller pore spaces (micropores) compared to sandy soils.
- **Option b** is incorrect because sandy soils allow faster infiltration; clayey soils have very slow infiltration rates.
- **Option c** is correct because low permeability is the primary physical characteristic that prevents drainage and causes waterlogging in clayey soils.
- **Option d** is incorrect because waterlogged clayey soils actually suffer from a lack of oxygen (hypoxia/anoxia) due to the displacement of air by water.
The duty of water is defined as:
A)
The depth of water required per hectare
B)
The amount of water required per unit crop area
C)
The number of hectares irrigated per unit discharge
D)
The loss of water due to evapotranspiration
In irrigation engineering, 'Duty' (D) is defined as the area of land that can be irrigated by a constant unit discharge of water flowing throughout the base period of the crop. It is typically expressed in hectares per cumec (ha/cumec).
Mathematically, Duty (D) = Area (A) / Discharge (Q).
Analysis of options:
- Option (a) and (b) describe 'Delta' (Δ), which is the total depth of water required by a crop during its entire growth period.
- Option (c) correctly defines 'Duty' as the relationship between the area irrigated and the rate of flow (discharge).
- Option (d) describes 'Evapotranspiration', which is a component of water loss, not a measure of duty.