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Past Questions — 2025
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.
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.
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.
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.
What is the significance of Kennedy’s silt theory in canal design?
A)
It determines the amount of sediment in a canal
B)
It helps design non-scouring and non-silting canals
C)
It calculates the velocity of flow in irrigation canals
D)
It determines the type of canal lining to use
Kennedy's Theory of Silt is a fundamental concept in canal engineering used to design stable channels. The primary objective of the theory is to determine the 'critical velocity' (also known as the regime velocity). If the actual velocity of flow in the canal is less than the critical velocity, silt will settle at the bottom (silting). If the velocity is significantly higher than the critical velocity, the bed and banks of the canal will be eroded (scouring). Therefore, by applying Kennedy's theory, engineers can design a canal that is 'regime'—meaning it is neither scouring nor silting, ensuring the canal maintains its cross-section and capacity over time.
Analysis of other options:
- Option (a) is incorrect because the amount of sediment is a characteristic of the water source, not something determined by the design theory.
- Option (c) is partially true in that it involves velocity, but the 'significance' is not just calculating velocity, but ensuring that velocity prevents both scouring and silting.
- Option (d) is incorrect as Kennedy's theory focuses on the hydraulic regime of unlined canals; lining is a separate design decision based on soil permeability and seepage losses.
Which of the following is NOT an effect of waterlogging?
A)
Reduced soil aeration
B)
Enhanced root respiration
C)
Increased salinity levels
D)
Stunted plant growth
Waterlogging occurs when the soil becomes saturated with water, filling the pore spaces that are normally occupied by air.
1. **Reduced soil aeration (Option a):** This is a direct effect of waterlogging. When water fills the soil pores, oxygen is displaced, leading to anaerobic conditions.
2. **Enhanced root respiration (Option b):** This is INCORRECT. Root respiration requires oxygen. In waterlogged soils, the lack of oxygen (hypoxia or anoxia) severely inhibits root respiration, forcing plants to switch to less efficient anaerobic fermentation, which can lead to the buildup of toxic ethanol and lactic acid.
3. **Increased salinity levels (Option c):** This is a common effect. Waterlogging often leads to a rise in the water table, which brings dissolved salts from deeper soil layers to the surface via capillary action. As the water evaporates, these salts accumulate in the root zone.
4. **Stunted plant growth (Option d):** This is a direct consequence. Due to the lack of oxygen for respiration and the potential increase in salinity or toxicity (e.g., manganese or iron toxicity), root development is impaired, nutrient uptake is reduced, and overall plant growth is stunted.
Since the question asks for what is NOT an effect, 'Enhanced root respiration' is the correct answer because waterlogging inhibits, rather than enhances, respiration.
Why is it essential to conduct levelling before constructing a highway?
A)
To determine the exact quantity of cement required
B)
To establish the correct elevation and drainage slopes
C)
To identify underground water sources
D)
To check soil fertility
Levelling is a branch of surveying used to determine the relative heights (elevations) of points on the earth's surface. In highway construction, it is critical for two primary reasons: 1) Elevation: To design the vertical alignment of the road, ensuring that gradients are safe for vehicles and that the road follows the natural terrain efficiently to minimize earthwork (cutting and filling). 2) Drainage: Water is the primary enemy of pavement. Levelling allows engineers to establish a 'camber' (cross-slope) and longitudinal slope, ensuring that rainwater drains off the road surface into side drains, preventing hydroplaning and structural deterioration of the road.
Why other options are incorrect:
- Option (a): Cement quantity is determined by the structural design and volume of the pavement, not by levelling.
- Option (c): Identifying underground water sources requires geophysical surveys or borehole drilling, not surface levelling.
- Option (d): Soil fertility is a concern for agriculture, not for the structural stability of a highway (which requires soil bearing capacity/CBR tests).
What is the primary assumption of Lacey’s silt theory?
A)
The canal should have a rectangular cross-section
B)
The canal reaches a stable section where no silting or scouring occurs
C)
The canal should have a high velocity to prevent sediment deposition
D)
The flow is always turbulent in all sections of the canal
Lacey's Silt Theory (developed by G.M. Lacey) is based on the concept of a 'Regime Channel.' The primary assumption is that a channel is in a state of 'regime' when it has automatically adjusted its cross-section, slope, and alignment to a state of equilibrium. In this stable state, the channel neither scours (erodes the bed) nor silts (deposits sediment), meaning the sediment transported is exactly equal to the sediment supplied.
Analysis of other options:
- Option (a) is incorrect because Lacey's theory specifically argues against fixed geometric shapes like rectangular sections, suggesting instead that the channel takes a natural, variable shape based on the silt factor.
- Option (c) is incorrect because the goal is not 'high velocity' but 'regime velocity'—a specific velocity that balances sediment transport.
- Option (d) is a general characteristic of most open channel flows but is not the 'primary assumption' upon which the silt theory's regime equations are built.
What is the primary purpose of agricultural drainage?
A)
To increase soil erosion
B)
To remove excess water and prevent waterlogging
C)
To increase soil acidity
D)
To promote water stagnation
Agricultural drainage is the removal of excess water from the soil surface or the root zone to create an optimal environment for plant growth.
1. Why Option (b) is correct: Excess water in the soil fills the pore spaces, displacing oxygen. This leads to anaerobic conditions (waterlogging), which suffocates plant roots, inhibits nutrient uptake, and can lead to root rot. Drainage systems (surface or subsurface) are implemented specifically to remove this surplus water and maintain the water table at a depth that allows roots to breathe.
2. Why Option (a) is incorrect: Soil erosion is the wearing away of topsoil. Drainage is designed to manage water, not to increase erosion; in fact, poorly managed drainage can sometimes cause erosion, but it is never the 'purpose'.
3. Why Option (c) is incorrect: Increasing soil acidity is generally detrimental to most crops. While drainage can affect soil chemistry (e.g., preventing the buildup of salts or managing redox potential), its primary purpose is not to increase acidity.
4. Why Option (d) is incorrect: Water stagnation is the exact problem that agricultural drainage is designed to solve. Promoting stagnation would lead to crop failure and soil degradation.
The key difference between plane and geodetic surveying is-
A)
The use of electronic instruments
B)
The type of data collected
C)
The consideration of earth’s curvature
D)
The number of surveyors required
In surveying, the primary distinction between plane surveying and geodetic surveying is based on how the shape of the earth is treated:
1. **Plane Surveying**: This method assumes the earth's surface to be a flat plane. The curvature of the earth is neglected. This is acceptable for small areas (typically less than 250 square kilometers) because the error introduced by ignoring the curvature is negligible.
2. **Geodetic Surveying**: This method takes into account the true spherical (or ellipsoidal) shape of the earth. It is used for large-scale surveys, such as national boundaries or state maps, where the curvature of the earth significantly affects the accuracy of measurements.
Analysis of other options:
- **Option a**: Both plane and geodetic surveying can use electronic instruments (like Total Stations or GPS).
- **Option b**: The type of data (distances, angles, coordinates) is fundamentally the same; only the mathematical treatment of that data differs.
- **Option d**: The number of surveyors depends on the project scale, not the theoretical method of surveying used.
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.
What is the most effective method to detect waterlogging?
A)
Checking soil color
B)
Measuring soil moisture content
C)
Observing plant height
D)
Measuring wind velocity
Waterlogging occurs when the soil becomes saturated, displacing air from the pore spaces and creating anaerobic (oxygen-poor) conditions. Under these conditions, chemical reduction occurs: iron (Fe3+) is reduced to ferrous iron (Fe2+), which reacts with the soil to create a characteristic 'gleying' effect. This results in the soil changing color to grey, bluish-grey, or greenish-grey. This color change is a permanent and highly reliable indicator of prolonged waterlogging.
Why other options are incorrect:
- b. Measuring soil moisture content: While this tells you the current amount of water, it does not distinguish between temporary saturation (after a rain event) and chronic waterlogging (poor drainage/high water table).
- c. Observing plant height: Stunted growth can be a symptom of waterlogging, but it is non-specific; it can also be caused by nutrient deficiency, pests, or drought.
- d. Measuring wind velocity: Wind velocity affects evaporation rates but is not a method to detect the presence of waterlogging in the soil profile.
The most common type of error in levelling is:
A)
Instrumental error
B)
Gross error
C)
Collimation error
D)
Systematic error
In levelling, errors are generally classified into three categories: Instrumental, Personal (Gross), and Natural. Among these, the most common and characteristic instrumental error is the Collimation Error.
1. Collimation Error: This occurs when the line of sight of the telescope is not perfectly horizontal when the bubble is centered. It is the most frequent error encountered in field levelling. It can be minimized by keeping the backsight and foresight distances equal (balancing the staff) or by performing a two-peg test to calibrate the instrument.
2. Instrumental Error (Option a): This is a broad category. While collimation error is a type of instrumental error, 'Collimation error' is the specific and most common type within this category for levelling.
3. Gross Error (Option b): These are caused by human mistakes (e.g., misreading the staff or recording the wrong value). While they happen, they are not 'systematic' or 'common' in the technical sense of instrument behavior; they are blunders to be avoided.
4. Systematic Error (Option d): This is a general classification of errors that follow a mathematical or physical law (including collimation error). However, when asked for the 'most common type' in the context of levelling, the specific technical term 'Collimation error' is the standard answer in surveying textbooks.
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.
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.
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.
A field with a gentle slope requires which type of drainage system to prevent waterlogging?
A)
Deep sub-surface drainage only
B)
Contour surface drainage channels
C)
No drainage is needed on gentle slopes
D)
Excess irrigation to balance water levels
Step-by-step reasoning:
1. **Analyze the Terrain**: A 'gentle slope' implies that water will naturally move downslope due to gravity, but if the slope is too slight or the soil permeability is low, water can still accumulate (waterlogging) or cause surface erosion.
2. **Evaluate Option (b)**: Contour surface drainage involves constructing channels across the slope (following the contour lines). This system is specifically designed for sloping lands to intercept surface runoff, reduce the velocity of water flow (preventing erosion), and direct excess water safely to a main outlet, thereby preventing waterlogging in the field.
3. **Evaluate Option (a)**: Deep sub-surface drainage is typically used for areas with high water tables or heavy clay soils regardless of slope, but for a field with a gentle slope, surface runoff management via contour channels is the primary and most efficient method to prevent surface waterlogging.
4. **Evaluate Option (c)**: This is incorrect because even gentle slopes can experience waterlogging if the soil is saturated or if the slope is not sufficient to drain the volume of precipitation/irrigation.
5. **Evaluate Option (d)**: This is logically incorrect; adding 'excess irrigation' would exacerbate waterlogging rather than prevent it.
Therefore, contour surface drainage is the most appropriate engineering solution for managing water on gently sloping agricultural land.
A properly designed surface drainage system should ensure which of the following?
A)
Rapid removal of all water from the field
B)
Slow movement of water with minimal erosion
C)
Water retention for long periods
D)
Reduction in soil permeability
In agricultural surface drainage, the primary objective is to remove excess water from the soil surface to prevent waterlogging and crop damage. However, the design must balance the speed of water removal with soil conservation.
1. Why option (b) is correct: If water moves too quickly across the surface, it gains kinetic energy, leading to significant soil erosion and loss of fertile topsoil. Therefore, a properly designed system ensures that water is guided away efficiently but at a controlled velocity (slow movement) to minimize erosion.
2. Why option (a) is incorrect: 'Rapid removal of all water' is dangerous because high-velocity runoff causes severe gully and sheet erosion, stripping the land of nutrients.
3. Why option (c) is incorrect: 'Water retention for long periods' is the opposite of the purpose of drainage. Drainage is intended to remove excess water, not retain it, as prolonged saturation leads to anaerobic conditions (lack of oxygen) which kills most crop roots.
4. Why option (d) is incorrect: 'Reduction in soil permeability' would hinder the movement of water into the soil or through the drainage system, exacerbating waterlogging issues rather than solving them.
Irrigation canals are generally aligned along-
A)
Ridgeline
B)
Valley line
C)
Contour line
D)
Both (a) & (b) as per the design requirement
In canal engineering, the alignment of a canal is critical for efficient water distribution.
1. **Ridgeline Alignment (Correct):** A canal aligned along the ridgeline (the highest line of a watershed) is known as a 'Ridge Canal'. The primary advantage of this alignment is that it allows the canal to irrigate land on both sides of the canal using gravity, which eliminates the need for expensive pumping or complex cross-drainage works. This maximizes the command area.
2. **Valley Line (Incorrect):** Aligning a canal along a valley line would cause the canal to be at the lowest point of the terrain. This would make it impossible to irrigate the surrounding higher lands by gravity and would require numerous expensive aqueducts to cross natural streams flowing into the valley.
3. **Contour Line (Incorrect):** While canals are often designed to follow a specific gradient (which involves following contours), a pure contour alignment (constant elevation) would result in zero flow (no slope). Canals must have a longitudinal slope to ensure water flows from the headworks to the tail end.
Therefore, for optimal command area and gravity-based distribution, the ridgeline is the preferred general alignment.
Which of the following factors does NOT influence canal alignment?
A)
Topography of the region
B)
Type of soil
C)
Number of people in the command area
D)
Availability of cross-drainage structures
Canal alignment refers to the layout of the centerline of a canal on the ground. The primary objective is to provide maximum irrigation to the command area with minimum cost and minimum loss of water.
1. Topography of the region (Option a): This is a critical factor. The canal is usually aligned along the contours of the land to ensure gravity flow and minimize expensive excavation or embankments.
2. Type of soil (Option b): Soil permeability and stability influence alignment. For example, permeable soils may require lining or a different route to avoid excessive seepage losses.
3. Availability of cross-drainage structures (Option d): The alignment is planned to minimize the number of crossings with natural drains (streams, rivers) to reduce the cost and complexity of constructing aqueducts, super-passages, or siphons.
In contrast, the 'Number of people in the command area' (Option c) is a socio-economic factor that might influence the *scale* or *justification* of the project, but it does not dictate the physical *alignment* (the geometric path) of the canal on the terrain.
What is the critical velocity ratio in irrigation canal design?
A)
Ratio of actual velocity to gravitational velocity
B)
Ratio of mean velocity to critical velocity
C)
Ratio of design velocity to maximum velocity
D)
Ratio of surface velocity to bottom velocity
In fluid mechanics and canal engineering, the 'critical velocity' refers to the velocity at which the specific energy is minimum for a given discharge. The ratio of the actual mean velocity (V) to the critical velocity (Vc) is known as the Froude Number (Fr) or the velocity ratio.
1. When V/Vc < 1, the flow is subcritical (tranquil).
2. When V/Vc = 1, the flow is critical.
3. When V/Vc > 1, the flow is supercritical (rapid).
Analyzing the options:
- Option (a) is incorrect as 'gravitational velocity' is not a standard term used in this ratio.
- Option (c) is incorrect because design velocity is a target value, not a physical ratio used to determine flow regime.
- Option (d) is incorrect as the ratio of surface to bottom velocity relates to the velocity distribution profile, not the critical velocity ratio.
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 open channel hydraulics, flow is classified based on the Froude Number (Fr), which is the ratio of inertial forces to gravitational forces.
1. **Subcritical Flow (Fr < 1):** This occurs when the flow velocity is low (slow) and the depth is relatively high. In this regime, surface waves can travel upstream. Consequently, any disturbance or change in conditions downstream (such as a weir, gate, or narrowing) propagates upstream and affects the flow. Therefore, subcritical flow is 'downstream controlled'.
2. **Supercritical Flow (Fr > 1):** This occurs when the flow velocity is high (fast) and the depth is low. Surface waves cannot travel upstream because the flow velocity exceeds the wave speed. Thus, the flow is 'upstream controlled'.
3. **Critical Flow (Fr = 1):** This is the transition state between subcritical and supercritical flow.
Evaluating the options:
- Option (a) is correct as it accurately describes the velocity (slow) and the control mechanism (downstream) of subcritical flow.
- 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).
Which of the following is NOT a primary method of levelling?
A)
Simple levelling
B)
Differential levelling
C)
Profile levelling
D)
Contour levelling
In surveying, levelling methods are generally categorized based on the purpose and the process of determining elevations.
1. **Simple Levelling (Option a):** This is a primary method used to find the difference in elevation between two points that are relatively close and visible from a single instrument station.
2. **Differential Levelling (Option b):** This is a primary method used to find the difference in elevation between two points that are far apart or separated by obstacles, requiring multiple instrument setups.
3. **Profile Levelling (Option c):** This is a primary method used to determine the elevation of a series of points along a fixed line (such as the centerline of a road or railway) to plot the longitudinal section.
4. **Contour Levelling (Option d):** While essential, contouring is considered an **application** or a specialized process of levelling rather than a primary method of determining elevation differences. Contouring uses the data obtained from either profile levelling or grid levelling to map lines of equal elevation. In many technical classifications of surveying, simple, differential, and profile levelling are the fundamental 'methods' of operation, whereas contouring is the 'objective' or the resulting map product.
Therefore, among the given options, Contour Levelling is the least likely to be classified as a 'primary method' of the levelling process itself.
Why is it important to consider the “Critical Velocity Ratio” in canal design?
A)
It determines whether the canal will experience erosion or sediment deposition
B)
It ensures that the water flows at the highest possible velocity
C)
It is used to calculate the amount of water required for irrigation
D)
It helps in increasing the depth of water in the canal
In canal engineering, the design must balance two conflicting requirements: the velocity must be high enough to prevent the deposition of silt (non-silting velocity) and low enough to prevent the erosion of the canal bed and banks (non-scouring velocity). The 'Critical Velocity' (or the ratio associated with it, often linked to the Kennedy's or Lacey's theories) is used to determine the 'regime' of the channel. If the actual velocity is lower than the critical velocity required to keep particles in suspension, sediment deposition occurs. If the velocity exceeds the permissible critical velocity for the soil type, scouring (erosion) occurs. Therefore, considering this ratio is essential to ensure the canal remains stable and maintains its cross-section over time.
Why other options are incorrect:
- Option b: Flowing at the 'highest possible velocity' would lead to severe scouring and destruction of the canal lining/banks.
- Option c: The amount of water required for irrigation is determined by crop water requirements and duty-delta calculations, not by velocity ratios.
- Option d: The depth of water is a design parameter based on discharge and velocity, but the purpose of the critical velocity ratio is stability, not simply increasing depth.