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Past Questions
A field has a length of 300 meters and a width of 150 meters. If 5 cm of irrigation water is applied, calculate the total volume of water required (in cubic meters).
A)
2250 m³
B)
1500 m³
C)
2500 m³
D)
3000 m³
To calculate the total volume of water required for irrigation, we use the formula: Volume = Area × Depth of water.
Step 1: Calculate the area of the field.
Area = Length × Width
Area = 300 m × 150 m = 45,000 m²
Step 2: Convert the depth of irrigation water from centimeters to meters to maintain unit consistency.
Depth = 5 cm = 5 / 100 m = 0.05 m
Step 3: Calculate the total volume.
Volume = 45,000 m² × 0.05 m
Volume = 2,250 m³
Therefore, the total volume of water required is 2,250 cubic meters. Option (a) is correct. Options (b), (c), and (d) are incorrect as they do not match the calculated volume based on the provided dimensions and depth.
GIS is mainly used for:
A)
Mapping and analyzing spatial data
B)
Measuring distances with high accuracy
C)
Estimating soil properties
D)
Conducting hydrographic surveys
GIS stands for Geographic Information System. It is a conceptualized framework that provides the ability to capture, store, manipulate, analyze, manage, and present all types of geographical or spatial data.
1. Why Option (a) is correct: GIS integrates hardware, software, and data to visualize, question, analyze, and interpret data to understand relationships, patterns, and trends. Its primary function is the management and analysis of spatial data (data linked to a specific location on Earth).
2. Why Option (b) is incorrect: Measuring distances with high accuracy is the primary function of surveying instruments like Total Stations, EDM (Electronic Distance Measurement), or Steel Tapes, not the GIS software system itself.
3. Why Option (c) is incorrect: Estimating soil properties is the domain of Geotechnical Engineering and Soil Mechanics, involving laboratory tests and field sampling (e.g., Standard Penetration Test).
4. Why Option (d) is incorrect: Conducting hydrographic surveys involves the use of Echo Sounders, Sonar, and specialized marine surveying equipment to map the bottom of water bodies. While the results of a hydrographic survey can be imported into a GIS for analysis, the act of 'conducting' the survey is a field operation, not a GIS function.
The most common type of error in levelling is:
A)
Instrumental error
B)
Gross error
C)
Collimation error
D)
Systematic error
In leveling, errors are generally classified into three categories: Instrumental, Personal (Gross), and Natural. Among these, the 'Collimation Error' is the most common and significant instrumental error. It occurs when the line of sight of the telescope is not perfectly horizontal (parallel to the axis of the bubble tube) when the instrument is leveled. This causes the line of sight to incline slightly upwards or downwards, leading to incorrect staff readings. While it is a type of systematic error, 'Collimation error' is the specific, most frequent technical error encountered in leveling operations.
Breakdown of other options:
- Instrumental error: This is a broad category. Collimation error is a specific type of instrumental error, making 'c' a more precise answer.
- Gross error: These are caused by human mistakes (e.g., misreading a number) and are avoided by careful work, not inherent to the process.
- Systematic error: This is a general category of errors that follow a mathematical law (including collimation error and curvature/refraction). Again, 'Collimation error' is the most common specific instance in leveling.
In levelling, the term “backsight” refers to-
A)
The last reading taken before moving the instrument
B)
The first reading taken from a known elevation
C)
A reading taken at a change point
D)
A reading used for error correction
In leveling, a Backsight (BS) is defined as the first staff reading taken after the leveling instrument (level) is set up. This reading is taken on a point of known elevation (either a Benchmark or a previously established point) to determine the Height of Instrument (HI).
Analysis of options:
- Option (a) describes a 'Foresight' (FS), which is the last reading taken before moving the instrument to a new position.
- Option (b) is correct as it describes the fundamental purpose of a backsight: establishing the instrument's elevation relative to a known point.
- Option (c) is partially true in practice (a reading at a change point can be a BS), but the definition of a BS is specifically the reading taken *back* toward a known point, whereas the reading taken *away* from the instrument at a change point is the FS. Option (b) is the more precise general definition.
- Option (d) is incorrect; while BS is used in calculations, it is not a specific 'reading used for error correction' (that would be a check reading or a closing reading).
In which situation is a contour canal preferred over a watershed canal?
A)
When the region has a flat terrain
B)
When the land has undulating topography with steep slopes
C)
When there are many natural streams in the area
D)
When the canal needs to avoid excessive excavation
In canal engineering, the choice between a watershed canal and a contour canal depends primarily on the topography of the land.
1. **Watershed Canal (Ridge Canal):** This canal is aligned along the ridge line (watershed) of the area. It allows irrigation on both sides of the canal through gravity. However, it is only feasible in regions where the ridge is relatively straight and the terrain is not excessively steep or undulating.
2. **Contour Canal:** A contour canal is aligned approximately parallel to the contours of the land. It is specifically preferred in hilly or undulating terrain where the land has steep slopes. Because it follows the natural contour, it minimizes the need for massive earthworks (cutting and filling) that would be required to maintain a ridge alignment in rugged terrain.
**Analysis of Options:**
- **Option (a):** In flat terrain, a ridge canal or a simple aligned canal is preferred; contouring is unnecessary.
- **Option (b):** Correct. In undulating topography with steep slopes, following the contour is the most practical way to maintain a steady gradient for water flow while minimizing construction costs.
- **Option (c):** The presence of natural streams affects the number of aqueducts or siphons needed, but it is not the primary deciding factor between watershed and contour alignment.
- **Option (d):** While contour canals do reduce excavation compared to a forced ridge alignment in hills, the *primary situation* that necessitates their use is the topography itself (undulating/steep slopes).
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) with a digital 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 mathematical computation, thereby improving the overall accuracy and efficiency of the survey.
2. Why Option (b) is incorrect: Total Stations use light/infrared waves (EDM) which require a line-of-sight. They cannot penetrate the ground to measure underground features; that would require Ground Penetrating Radar (GPR) or seismic surveying.
3. Why Option (c) is incorrect: Every survey requires a reference point (benchmark or known station) to establish a coordinate system. A Total Station still needs a known starting point and orientation to provide absolute coordinates.
4. Why Option (d) is incorrect: While some high-end Total Stations allow the user to input atmospheric corrections (temperature and pressure) to adjust the EDM's speed of light calculations, they do not 'automatically' adjust for all atmospheric conditions without input or calibration; more importantly, this is a feature of the EDM component, whereas the primary systemic improvement over a theodolite is the integration of measurement and calculation.
If a rain gauge recorded 50 mm of rainfall in 10 hours, what is the average intensity of rainfall?
A)
2.5 mm/hr
B)
5 mm/hr
C)
7.5 mm/hr
D)
10 mm/hr
The average intensity of rainfall is defined as the total depth of precipitation recorded divided by the duration of the rainfall event.
Given data:
- Total rainfall depth (P) = 50 mm
- Duration of rainfall (t) = 10 hours
Formula:
Average Intensity (I) = Total Rainfall / Duration
I = 50 mm / 10 hours
I = 5 mm/hr
Evaluating the options:
- Option (a) 2.5 mm/hr is incorrect as it would result from 25 mm of rain in 10 hours.
- Option (b) 5 mm/hr is correct based on the calculation.
- Option (c) 7.5 mm/hr is incorrect as it would result from 75 mm of rain in 10 hours.
- Option (d) 10 mm/hr is incorrect as it would result from 100 mm of rain in 10 hours.
What does the term “Crop Water Requirement” refer to?
A)
The amount of water needed to cultivate a crop per year
B)
The total water required for a crop to grow and yield optimally
C)
The amount of water applied through irrigation alone
D)
The total groundwater required for irrigation
Step-by-step reasoning:
1. **Definition**: Crop Water Requirement (CWR) is defined as the total quantity of water required by a crop for its normal growth and yield. This includes water used for transpiration by the plant and water evaporated from the soil surface and plant parts (collectively known as Evapotranspiration, ET).
2. **Components**: CWR accounts for the water needed to replace losses due to evapotranspiration and to satisfy the metabolic needs of the plant throughout its growth cycle.
3. **Analysis of Options**:
- **Option (a)** is incorrect because CWR is not just a yearly figure; it is specific to the growth cycle of the crop and varies by crop type and climate.
- **Option (b)** is correct as it encompasses the total water necessity (from all sources, including rain) to ensure optimal growth and yield.
- **Option (c)** is incorrect because this describes 'Irrigation Requirement'. Irrigation requirement is the portion of the Crop Water Requirement that is not met by effective rainfall.
- **Option (d)** is incorrect because CWR refers to the biological need of the plant, regardless of whether the water source is groundwater, surface water, or precipitation.
The primary purpose of stream gauging station is-
A)
River velocity only
B)
Streamflow and discharge
C)
Rainfall intensity
D)
Groundwater table levels
A stream gauging station is a facility established at a specific point along a river or stream to monitor and measure the volume of water moving past that point over time.
1. **Streamflow and Discharge**: The primary objective of these stations is to determine the 'discharge' (Q), which is the volume of water flowing per unit of time (typically measured in m³/s or cusecs). Discharge is calculated using the formula Q = A × V, where A is the cross-sectional area of the channel and V is the average velocity of the flow.
2. **Why other options are incorrect**:
- **Option a (River velocity only)**: While velocity is measured at a gauging station, it is merely a component used to calculate the total discharge. Measuring velocity alone does not fulfill the primary purpose of gauging the stream's flow volume.
- **Option c (Rainfall intensity)**: This is measured by rain gauges (pluviometers), not stream gauging stations.
- **Option d (Groundwater table levels)**: This is measured using observation wells or piezometers, which monitor the phreatic surface of an aquifer, not the surface flow of a stream.
Which factor does NOT directly influence the crop water requirement?
A)
Soil type
B)
Crop type
C)
Wind speed
D)
Crop market price
Crop water requirement (CWR) is the total quantity of water required by a crop for its growth from sowing to harvesting. It is primarily determined by the Evapotranspiration (ET) rate and the water needed to moisten the soil.
1. **Crop type (Option b):** Different crops have different root depths, growth stages, and transpiration rates (represented by the crop coefficient Kc), directly affecting water needs.
2. **Wind speed (Option c):** Wind increases the rate of transpiration and evaporation by removing the boundary layer of moisture from the leaf surface, thereby increasing the water requirement.
3. **Soil type (Option a):** Soil texture (sandy vs. clayey) determines the water-holding capacity and infiltration rate, which directly influences how much irrigation water is needed to maintain the root zone moisture.
4. **Crop market price (Option d):** This is an economic factor. While it may influence a farmer's decision on *whether* to plant a crop or how much to invest in irrigation, it has no biological or physical effect on the actual amount of water the plant requires to survive and grow.
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 water input or increasing water removal.
- Option (a) 'Using well-planned irrigation techniques' (such as drip or sprinkler irrigation) prevents over-watering, thus preventing waterlogging.
- Option (b) 'Installing drainage systems' (such as surface or subsurface drains) allows excess water to exit the root zone, directly preventing waterlogging.
- Option (d) 'Using raised beds for planting' improves aeration and allows excess water to drain away from the plant roots into the furrows, preventing saturation of the root zone.
- 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 already prone to waterlogging, this practice does nothing to mitigate the physical condition of the soil and may lead to salinity or alkalinity issues in other crop cycles.
Contour lines that are very close together indicate:
A)
Flat terrain
B)
A steep slope
C)
A river valley
D)
A depression in the land
In surveying, contour lines are imaginary lines connecting points of equal elevation. The spacing between these lines represents the rate of change in elevation over a horizontal distance (the slope).
1. **Steep Slope:** When contour lines are very close together, it means the elevation is changing rapidly over a short horizontal distance, which indicates a steep slope.
2. **Flat Terrain:** Conversely, when contour lines are widely spaced, the elevation changes slowly over a large distance, indicating flat or gentle terrain.
3. **River Valley:** A river valley is typically represented by V-shaped contours with the apex of the 'V' pointing upstream.
4. **Depression:** A depression is indicated by closed contour lines with hachure marks (small ticks) pointing inwards toward the center of the depression.
Therefore, closely spaced contours are the definitive characteristic of a steep slope.
What does a hydrograph represent?
A)
Changes in groundwater table over time
B)
Flow variations in a stream over time
C)
Rainfall intensity variations
D)
Soil moisture variations
A hydrograph is a fundamental tool in hydrology defined as a graph showing the rate of flow (discharge) versus time past a specific point in a river or stream.
Step-by-step reasoning:
1. Definition: The term 'hydro' refers to water and 'graph' refers to a plot. In engineering hydrology, it specifically tracks the discharge (Q) of a stream over a period of time (t).
2. Analysis of Options:
- Option (a) describes a 'water table fluctuation' or 'piezometric head' plot, not a hydrograph.
- Option (b) correctly identifies the relationship between stream flow (discharge) and time.
- Option (c) describes a 'hyetograph', which is a plot of rainfall intensity versus time.
- Option (d) describes soil moisture profiles or monitoring, which is a different parameter of the hydrological cycle.
3. Conclusion: Since a hydrograph measures the response of a catchment to a rainfall event by plotting the resulting streamflow, option (b) is the correct technical definition.
Which of the following is NOT a type of surface drainage system?
A)
Open ditches
B)
Graded border system
C)
Tile drainage
D)
Field drains
Agricultural drainage systems are broadly classified into two categories: Surface Drainage and Sub-surface Drainage.
1. Surface Drainage: This involves the removal of excess water from the soil surface. Examples include:
- Open ditches (Option a): Excavated channels that collect and carry away surface water.
- Graded border system (Option b): A method where the field is graded to allow water to flow toward a collector drain.
- Field drains (Option d): Small channels within a field used to move surface water to larger drains.
2. Sub-surface Drainage: This involves the removal of excess water from the root zone (below the soil surface).
- Tile drainage (Option c): This uses perforated pipes (originally clay tiles, now mostly plastic) buried underground to lower the water table. Because these pipes are installed below the surface, it is a sub-surface drainage system, not a surface drainage system.
Therefore, Tile drainage is the correct answer as it is NOT a type of surface drainage.
Which of the following best describes a catchment area?
A)
A low-lying region with high rainfall
B)
An area where rainfall is completely absorbed
C)
A region from which all precipitation drains into a common outlet
D)
A part of a river prone to flooding
Step-by-step reasoning:
1. Definition: In hydrology, a catchment area (also known as a drainage basin or watershed) is the entire geographical area from which surface runoff and groundwater flow into a single point, such as a river, lake, or reservoir (the common outlet).
2. Analysis of Option (a): A low-lying region with high rainfall describes a specific climatic or topographic condition, not the functional definition of a catchment.
3. Analysis of Option (b): An area where rainfall is completely absorbed describes a region with high infiltration or a 'sink,' whereas a catchment is defined by the movement of water toward an outlet.
4. Analysis of Option (c): This aligns perfectly with the scientific definition. The boundaries of a catchment are defined by topographic ridges (divides) that direct all precipitation within that boundary toward a common exit point.
5. Analysis of Option (d): A part of a river prone to flooding describes a 'floodplain,' which is a feature within a catchment, but not the catchment area itself.
Effective rainfall is defined as:
A)
The total rainfall in a catchment
B)
The portion of rainfall that contributes to runoff and infiltration
C)
Rainfall that evaporates before reaching the ground
D)
The amount of rainfall stored in lakes
Effective rainfall (also known as excess rainfall) is the portion of the total precipitation that becomes direct runoff from a catchment area. In hydrology, when rain falls on a watershed, some of it is intercepted by vegetation, some evaporates, and a significant portion infiltrates into the soil to recharge groundwater. The 'effective' part is the remaining water that exceeds the infiltration capacity of the soil and flows over the land surface as surface runoff, which eventually reaches the stream or outlet.
Analysis of options:
- Option (a) is incorrect because total rainfall includes water that is lost to evaporation and interception.
- Option (b) is correct as it identifies the portion that actually contributes to the hydrological response (runoff) and the subsurface movement (infiltration/baseflow).
- Option (c) describes 'interception loss' or 'evaporation', not effective rainfall.
- Option (d) describes 'surface storage', which is a result of rainfall but not the definition of effective rainfall.
If the flow in an irrigation canal is subcritical, what does it indicate?
A)
The flow is slow and controlled by downstream conditions
B)
The flow is fast and controlled by upstream conditions
C)
The canal is in supercritical flow
D)
The flow is always uniform
In fluid mechanics, flow is classified based on the Froude Number (Fr), where Fr = v / √(gD).
1. Subcritical Flow (Fr < 1): This occurs when the flow velocity is low (slow) relative to the wave speed. In this regime, disturbances (waves) can travel upstream. Consequently, the water level and flow characteristics are influenced by downstream conditions (e.g., a weir, a gate, or a narrowing downstream). This is typical for most irrigation canals to prevent erosion of the canal bed.
2. Supercritical Flow (Fr > 1): This occurs when the flow velocity is high (fast). Disturbances cannot travel upstream; therefore, the flow is controlled by upstream conditions (e.g., the slope of the channel or the headwater level).
Evaluating the options:
- Option (a) is correct because subcritical flow is characterized by low velocity and downstream control.
- Option (b) describes supercritical flow.
- Option (c) is a contradiction; subcritical flow cannot be supercritical flow.
- Option (d) is incorrect because subcritical flow can be either uniform or non-uniform (varied flow).
Why does the duty of water increase as it moves downstream?
A)
Water loss due to infiltration
B)
Water use efficiency improves
C)
Reduction in seepage losses
D)
None of the above
To solve this question, we must first understand the definition of 'Duty'. 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 period. The formula is Duty = Area / Discharge.
As water moves downstream in a canal system, it is subject to losses due to evaporation and seepage (infiltration into the ground). Consequently, the actual discharge (Q) available at the downstream end is less than the discharge at the head of the canal.
Since Duty is inversely proportional to the discharge required to irrigate a unit area (D = 8.64B / Δ), if we consider a fixed volume of water released at the head, the amount of water actually reaching the downstream fields is reduced. To irrigate the same area downstream, a higher discharge is required at the head to compensate for these losses. Therefore, the 'Duty' (the area irrigated per unit of water delivered at the source) actually DECREASES as water moves downstream because more water is 'wasted' to reach the destination.
Analyzing the options:
- Option (a): Water loss due to infiltration/seepage causes the duty to decrease, not increase.
- Option (b): Water use efficiency generally does not improve simply by moving downstream; in fact, conveyance losses reduce overall system efficiency.
- Option (c): Seepage losses typically occur throughout the canal; they do not 'reduce' in a way that would increase the duty of the water.
Since the duty of water decreases (not increases) as it moves downstream due to conveyance losses, none of the provided reasons explain an 'increase' in duty. Therefore, the correct option is 'None of the above'.
Why is the selection of a particular type of irrigation system highly dependent on soil type?
A)
Some soils absorb water too quickly, making certain methods inefficient
B)
All irrigation methods work equally well, regardless of soil type
C)
Soil type only affects crop growth, not the irrigation method
D)
Irrigation system selection is only based on water availability
The selection of an irrigation system is fundamentally based on the soil's hydraulic properties, specifically its infiltration rate and water-holding capacity.
1. **Infiltration Rate:** Sandy soils have high infiltration rates (water absorbs quickly). If a surface irrigation method like flood or furrow irrigation is used on sandy soil, the water will seep deep into the ground before it can reach the end of the field, leading to massive water waste and uneven distribution. In such cases, drip or sprinkler irrigation is preferred.
2. **Water Retention:** Clayey soils have low infiltration rates and high water retention. Using high-volume surface irrigation on clay can lead to waterlogging and anaerobic conditions for roots.
Evaluating the options:
- **Option a** is correct because it accurately describes how soil permeability (absorption speed) dictates the efficiency of the irrigation method.
- **Option b** is incorrect because different soils react differently to water application (e.g., flood irrigation is inefficient in sand).
- **Option c** is incorrect because soil type affects both the biological growth of the crop and the physical movement of water (hydraulics).
- **Option d** is incorrect because while water availability is a factor, it is not the *only* factor; soil type, topography, and crop type are equally critical.
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 triangulation and traversing.
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 (unless it is a Total Station, which is a combination of a theodolite and an EDM).
4. **Why Option (d) is incorrect:** Capturing digital data with automated processing describes a Total Station or GPS/GNSS receiver. A traditional theodolite is an optical instrument requiring manual readings.
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, traversing is the process of establishing a series of connected lines.
1. **Closed Traverse (Option b):** A closed traverse starts and ends at the same point or connects two known points. 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. Furthermore, because it closes on itself, it allows for the calculation of the 'closing error,' enabling the surveyor to check for accuracy and distribute errors mathematically (using methods like Bowditch's rule), which is critical when the path is irregular due to obstacles.
2. **Open Traverse (Option a):** An open traverse does not return to the starting point or close on a known point. It is used for linear features like roads or rivers. It provides no way to check for cumulative errors, making it unreliable for complex areas with obstacles.
3. **Radial Traverse (Option c):** In a radial traverse, all lines are measured from a single central point. This is only feasible 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):** While triangulation is a highly accurate method for large areas, it relies on the creation of a network of triangles. It requires clear inter-visibility between stations. In an area with many obstacles, establishing these clear lines of sight for a triangle network is significantly more difficult than simply 'walking' a closed traverse around the obstacles.
Calculate the intensity of irrigation if the Gross Command Area (GCA) is 5000 hectares and the Culturable Command Area (CCA) is 4000 hectares.
A)
80%
B)
75%
C)
85%
D)
90%
Step-by-step calculation:
1. **Definitions**:
- **Gross Command Area (GCA)**: The total area that can be irrigated by a canal system, including forests, roads, villages, and wasteland.
- **Culturable Command Area (CCA)**: The portion of the GCA that is actually fit for cultivation.
- **Intensity of Irrigation**: This is defined as the ratio of the area actually irrigated to the Culturable Command Area (CCA), expressed as a percentage. However, in many standard textbook problems where the 'area actually irrigated' is not explicitly given separately from the CCA, the intensity of irrigation is calculated as the ratio of CCA to GCA to determine the proportion of the total command area that is cultivable.
2. **Formula**:
Intensity of Irrigation (%) = (CCA / GCA) × 100
3. **Substitution**:
Given GCA = 5000 hectares
Given CCA = 4000 hectares
Intensity = (4000 / 5000) × 100
Intensity = 0.8 × 100 = 80%
Therefore, the intensity of irrigation is 80%. Option (a) is correct, while options (b), (c), and (d) are mathematically incorrect based on the provided data.
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 efficiently. The ability of soil to transmit water is known as permeability (or hydraulic conductivity).
1. **Clayey Soils:** These soils consist of very fine particles that pack closely together. While they have a high total porosity (more total void space), the individual pores are microscopic (micropores). These small pores create high friction and capillary forces that significantly restrict the movement of water, resulting in low permeability. Consequently, water accumulates in the root zone, leading to waterlogging.
2. **Sandy Soils:** These consist of larger particles with larger interconnected spaces (macropores). This allows water to move rapidly through the soil profile via gravity, resulting in high permeability and a lower risk of waterlogging.
Evaluating the options:
- **Option a** is incorrect because clayey soils have smaller individual pore spaces (micropores) compared to sandy soils.
- **Option b** is incorrect because clayey soils have much slower infiltration rates due to their fine texture.
- **Option d** is incorrect because waterlogging actually displaces oxygen from the soil, leading to anaerobic conditions; clayey soils do not 'absorb more oxygen' to prevent waterlogging.
What is the major disadvantage of side slope canals?
A)
High construction cost
B)
Excessive water loss due to seepage
C)
Prone to landslides and slope instability
D)
Requires pumping stations
In canal engineering, 'side slope canals' refers to the standard trapezoidal cross-section used for most unlined canals. The major disadvantage of this design, particularly when constructed in pervious soils, is the large wetted perimeter relative to the flow area. Because the water is in direct contact with the soil along the side slopes and the bed, there is a significant amount of water loss through seepage into the ground. To mitigate this, lining (such as concrete or LDPE) is often required.
Evaluating other options:
- (a) High construction cost: Side slope (trapezoidal) canals are generally the most economical to excavate compared to complex reinforced structures.
- (c) Prone to landslides: While slope stability is a design consideration, it is a failure mode rather than a general 'major disadvantage' of the canal type itself, provided the slope is designed according to the angle of repose of the soil.
- (d) Requires pumping stations: Pumping stations are required based on the topography (lift irrigation) and the head of the water source, not based on the cross-sectional shape (side slopes) of the canal.
If a river has a cross-sectional area of 30 m² and the velocity of flow is 2 m/s, what is the discharge?
A)
30 m³/s
B)
50 m³/s
C)
60 m³/s
D)
90 m³/s
To calculate the discharge (Q) of a river, we use the Continuity Equation for steady flow: Q = A × V, where 'A' is the cross-sectional area of the flow and 'V' is the average velocity of flow.
Given:
- Cross-sectional area (A) = 30 m²
- Velocity of flow (V) = 2 m/s
Calculation:
Q = 30 m² × 2 m/s = 60 m³/s.
Therefore, the discharge is 60 cubic meters per second.
- Option (a) 30 m³/s is incorrect as it only considers the area.
- Option (b) 50 m³/s is mathematically incorrect.
- Option (d) 90 m³/s is mathematically incorrect.