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Past Questions — 2025
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 and analyze spatial and geographic data. GIS integrates hardware, software, and data to store, manipulate, analyze, and display all types of geographical data.
Why other options are incorrect:
- Option (b): Measuring distances with high accuracy is the primary function of surveying instruments like Total Stations, EDM (Electronic Distance Measurement), or Tapes, not the GIS software system itself.
- Option (c): Estimating soil properties is the domain of Geotechnical Engineering and Soil Mechanics, involving laboratory tests and field borings.
- Option (d): Conducting hydrographic surveys involves the use of Echo Sounders and specialized marine surveying equipment to map underwater topography; while the results can be imported into a GIS, the 'conducting' of the survey is a field operation, not a GIS function.
A wheat crop has a base period of 120 days and requires a total depth of water (Delta) of 60 cm. Calculate the Duty (in hectares per cumec).
A)
172.8 ha/cumec
B)
185.5 ha/cumec
C)
150.2 ha/cumec
D)
160.0 ha/cumec
To calculate the Duty of water, we use the standard relationship between Duty (D), Delta (Δ), and Base Period (B).
1. **Given Data:**
- Base Period (B) = 120 days
- Total depth of water (Delta, Δ) = 60 cm = 0.60 meters
2. **Formula:**
The relationship is given by the formula:
Duty (D) = (8.64 * B) / Δ
Where:
- D is the Duty in hectares per cumec (ha/cumec)
- B is the Base Period in days
- Δ is the Delta in meters
3. **Calculation:**
D = (8.64 * 120) / 0.60
D = 1036.8 / 0.60
D = 1728 / 1
Wait, let's re-calculate carefully:
1036.8 divided by 0.6 is equal to 1728.
Let's verify using the fundamental definition:
Duty (D) = Area / Discharge
Total volume of water required = Area * Delta = Discharge * Base Period
D = (Discharge * B * 24 * 60 * 60) / (Delta * 10000)
D = (1 * 120 * 86400) / (0.6 * 10000)
D = 10,368,000 / 6,000
D = 1728 ha/cumec.
Reviewing the options provided:
a. 172.8 ha/cumec
b. 185.5 ha/cumec
c. 150.2 ha/cumec
d. 160.0 ha/cumec
There is a decimal placement discrepancy in the options provided in the prompt (1728 vs 172.8). However, based on the numerical digits, option (a) is the only one that matches the calculation. In many competitive exam contexts, if a typo exists in the options (e.g., a missing zero or misplaced decimal), the option with the correct significant figures is selected. Mathematically, the result is 1728, but among the choices, 172.8 is the intended answer despite the decimal error in the question's options list.
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, we use the formula for the volume of a rectangular prism: Volume = Length × Width × Depth.
1. **Identify the given parameters:**
- Length (L) = 300 m
- Width (W) = 150 m
- Depth of water (d) = 5 cm
2. **Convert all units to meters (SI units):**
Since the length and width are in meters, the depth must also be in meters to ensure the final volume is in cubic meters (m³).
- Depth (d) = 5 cm = 5 / 100 m = 0.05 m
3. **Calculate the Volume:**
- Volume = 300 m × 150 m × 0.05 m
- Volume = (300 × 150) × 0.05
- Volume = 45,000 × 0.05
- Volume = 2,250 m³
Therefore, the total volume of water required is 2,250 m³. Option (a) is correct. Options (b), (c), and (d) are incorrect as they result from calculation errors or failure to convert units correctly.
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 objective of the operation.
1. **Simple Levelling (Option a):** This is a primary method used to find the difference in elevation between two points that are relatively close to each other and can be seen 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 it uses the techniques of the above methods, contouring is considered an **application** or a specialized process of levelling used to map the topography of a land area by joining points of equal elevation. It is not a 'primary method' of determining elevation difference, but rather a method of representing the surface of the earth on a map using the data derived from primary levelling methods.
Therefore, among the given options, contour levelling is the one that is not classified as a primary method of levelling.
What is the primary function of an irrigation canal?
A)
Transport of wastewater
B)
Storage of water
C)
Distribution of water for agriculture
D)
Generation of hydroelectricity
Step-by-step reasoning: 1. Definition: An irrigation canal is an artificial channel constructed to convey water from a source (such as a river, reservoir, or dam) to agricultural fields. 2. Primary Purpose: The fundamental goal of irrigation is to provide a controlled supply of water to crops to ensure growth, especially in areas with inadequate rainfall. 3. Evaluating Options: (a) Transport of wastewater is the function of a sewer or drainage system. (b) Storage of water is the primary function of a reservoir or tank, not a canal (which is for conveyance). (d) Generation of hydroelectricity is the function of a power plant/dam using a penstock, not an irrigation canal. Therefore, option (c) is the only correct description of the primary function of an irrigation canal.
Which crop season in India typically requires the highest irrigation?
A)
Kharif
B)
Rabi
C)
Zaid
D)
Monsoon
In India, crop seasons are primarily categorized based on the monsoon cycle.
1. **Kharif Season**: This is the 'monsoon crop' season (June to October). Crops like rice, maize, and cotton are grown during this period. Since these crops are sown and grown during the rainy season, they rely heavily on precipitation, and thus require relatively less artificial irrigation compared to Rabi crops.
2. **Rabi Season**: This is the 'winter crop' season (October to March). Major crops include wheat, mustard, and barley. This season coincides with the dry winter months when there is very little to no rainfall. Consequently, almost the entire water requirement for Rabi crops must be met through artificial irrigation (canals, tube wells, etc.), making it the season with the highest irrigation demand.
3. **Zaid Season**: This is a short season between Rabi and Kharif (March to June). While crops like watermelon and cucumber are grown and require irrigation due to the heat, the total volume of water required for the entire Zaid season is significantly lower than that of the Rabi season due to the smaller scale of cultivation.
4. **Monsoon**: This is a climatic period, not a specific crop season (though it overlaps with Kharif).
Therefore, because the Rabi season occurs during the driest part of the year, it typically requires the highest amount of irrigation.
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 maximum discharge
D)
It determines the slope of the canal
Kennedy's silt theory is a fundamental concept in irrigation engineering used to design stable alluvial canals. The primary objective of the theory is to determine the 'critical velocity' (V_c) of water. If the actual velocity of flow in the canal is less than the critical velocity, the silt will settle down (silting); if the velocity is significantly higher than the critical velocity, the bed material will be eroded (scouring). By designing the canal such that the velocity is approximately equal to the critical velocity, the engineer ensures a 'regime' condition where the canal is neither scouring nor silting.
Analysis of other options:
- Option (a) is incorrect because the amount of sediment is an input parameter (silt load), not something determined by the theory itself.
- Option (c) is incorrect because maximum discharge is determined by the required irrigation demand and the cross-sectional area/slope, not specifically by silt theory.
- Option (d) is partially true in practice (as slope is adjusted to achieve critical velocity), but the 'significance' or ultimate goal of the theory is the stability (non-scouring/non-silting) of the canal.
Irrigation canals are generally aligned along-
A)
Ridgeline
B)
Valley line
C)
Contour line
D)
Both (a) & (b) as per the design requirement
In irrigation engineering, the alignment of a canal is critical for efficient water distribution.
1. **Ridgeline Alignment (Watershed Alignment):** A canal aligned along the ridgeline (the highest point of the land) is known as a 'Watershed Canal'. The primary advantage of this alignment is that it allows the canal to irrigate land on both sides of the canal using gravity. This maximizes the command area and minimizes the need for expensive pumping or cross-drainage works.
2. **Contour Alignment:** While canals often follow a contour to maintain a steady slope (gradient), a pure contour alignment only allows irrigation on one side (the downhill side), which is less efficient than a ridgeline alignment.
3. **Valley Line Alignment:** Aligning a canal along a valley line is generally avoided because it would require the canal to be elevated on embankments or would lead to the canal acting as a drain for the surrounding area, necessitating numerous and costly cross-drainage structures (like aqueducts or siphons) to handle natural streams crossing the valley.
Therefore, for maximum command area and gravity-based distribution, the ridgeline is the preferred general alignment.
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 = Area / Discharge.
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 the definition of duty.
Which statement best describes the relationship between Delta, Duty, and Base Period?
A)
Higher Delta leads to lower Duty
B)
Lower Base Period increases Delta
C)
Duty is independent of Base Period
D)
Higher Duty reduces Base Period
The relationship between Duty (D), Delta (Δ), and Base Period (B) is defined by the fundamental irrigation formula:
Δ = (8.64 * B) / D
Or rearranged as:
D = (8.64 * B) / Δ
Where:
- Δ (Delta) is the total depth of water required by a crop during the entire base period (measured in meters or cm).
- D (Duty) is the area of land that can be irrigated by a unit discharge of water flowing continuously for the base period (measured in hectares/cumec).
- B (Base Period) is the time between the first watering and the last watering of a crop (measured in days).
Analysis of the options:
1. Option (a): According to the formula D = (8.64 * B) / Δ, Duty (D) is inversely proportional to Delta (Δ). Therefore, if the total depth of water required (Delta) increases, the area that a unit of water can cover (Duty) decreases. This is correct.
2. Option (b): Delta is a characteristic of the crop and the soil; it is not increased by lowering the Base Period. In fact, Delta is the total water depth over the entire Base Period.
3. Option (c): Duty is directly proportional to the Base Period (D ∝ B). If the base period increases, the same unit of water can serve a larger area over time. Thus, Duty is not independent of the Base Period.
4. Option (d): Higher Duty means the water is used more efficiently to cover more area; it does not inherently reduce the biological Base Period of the crop.
Plane table surveying is best suited for-
A)
Large-scale geodetic surveys
B)
Highly accurate and precise measurements
C)
Quick and small-scale mapping
D)
Hydrographic surveys
Plane table surveying is a graphical method of surveying where field observations and plotting are done simultaneously.
1. Why Option (c) is correct: Because the plotting is done in the field, there is no need for separate field notes or office-based plotting. This makes the process very fast (quick). It is typically used for filling in details between primary control points or for mapping small areas where extreme precision is not the primary requirement, making it ideal for quick, small-scale mapping.
2. Why Option (a) is incorrect: Geodetic surveys account for the curvature of the earth and require extremely high precision and complex calculations. Plane table surveying assumes the earth is a flat plane, making it unsuitable for geodetic surveys.
3. Why Option (b) is incorrect: Plane table surveying is generally less accurate than theodolite or total station surveying because it is subject to errors in plotting and sighting in the field.
4. Why Option (d) is incorrect: Hydrographic surveys involve mapping water bodies. Plane table surveying requires a stable, flat surface to set up the board and direct line-of-sight to land-based features, which is not applicable to underwater or deep-water mapping.
What instrument is used to measure rainfall?
A)
Anemometer
B)
Barometer
C)
Rain gauge
D)
Hygrometer
The correct instrument for measuring rainfall is the Rain gauge. It collects precipitation over a set period, and the depth is measured in millimeters (mm) or inches.
Analysis of other options:
- a. Anemometer: Used to measure wind speed and direction.
- b. Barometer: Used to measure atmospheric pressure.
- d. Hygrometer: Used to measure the humidity (moisture content) in the air.
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 (Horizontal:Vertical). This means for every 1 unit of vertical depth, the width increases by 1 unit on each side.
2. **Formula for Top Width (T):**
The top width of a trapezoidal channel is calculated as:
T = b + 2 * (z * d)
3. **Calculation:**
- Horizontal projection of one side slope = z * d = 1 * 2 m = 2 m
- Since there are two side slopes (left and right), the total increase in width is 2 * 2 m = 4 m.
- Top Width (T) = 4 m (bottom width) + 4 m (side projections) = 8 m.
4. **Verification of Options:**
- Option (a) 6m: Incorrect. This would occur if the side slope was 0.5:1.
- Option (b) 8m: Correct.
- 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.
Which factor has the most significant impact on the duty of water in an irrigation system?
A)
Type of irrigation method
B)
Rainfall in the region
C)
Soil fertility
D)
Crop maturity duration
Duty of water is defined as the area of land that can be irrigated with a unit volume of water flowing at a constant rate throughout the base period. The efficiency of water application is the primary driver of duty.
1. **Type of irrigation method (Correct):** This has the most significant impact because different methods have vastly different efficiencies. For example, drip irrigation has very high efficiency (low water waste), leading to a very high duty. In contrast, flood irrigation has high seepage and evaporation losses, leading to a low duty. The method of application directly determines how much of the supplied water actually reaches the root zone.
2. **Rainfall in the region:** While rainfall affects the 'net irrigation requirement,' duty is typically calculated based on the water supplied by the irrigation system. Rainfall is an external supplement rather than a factor that changes the inherent efficiency (duty) of the system itself.
3. **Soil fertility:** Soil fertility relates to nutrient content, not water-holding capacity or conveyance efficiency. While soil *texture* (sandy vs. clayey) affects duty, *fertility* does not.
4. **Crop maturity duration:** This affects the 'base period' (the time between first and last watering). While it influences the total volume of water needed, the efficiency of the delivery method (the irrigation system) remains the dominant factor in determining how much area a unit of water can serve.
Which factor plays the most crucial role in determining the irrigation efficiency of a system?
A)
Type of crop
B)
Water conveyance losses
C)
Canal length
D)
Depth of irrigation
Irrigation efficiency is generally defined as the ratio of the volume of water used beneficially by the crop to the volume of water diverted from the source. It is composed of several components: conveyance efficiency, application efficiency, and storage efficiency.
1. **Water conveyance losses (Option b):** These occur between the source (dam/river) and the field due to seepage and evaporation. In many irrigation systems, especially unlined canal systems, conveyance losses are the most significant source of water waste. Reducing these losses directly and drastically increases the overall system efficiency.
2. **Type of crop (Option a):** While different crops have different water requirements (crop coefficient), the 'efficiency' of the system refers to how well the water is delivered and used, not how much the crop needs.
3. **Canal length (Option c):** Canal length is a contributing factor to conveyance losses (longer canals generally have more seepage), but it is not the 'factor' itself; the 'loss' is the critical metric.
4. **Depth of irrigation (Option d):** This relates to application efficiency (how much water reaches the root zone), but system-wide efficiency is most heavily impacted by the massive losses that occur during the transport (conveyance) phase before the water even reaches the field.
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 levelling, a Backsight (BS) is defined as the first staff reading taken after the instrument 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.
- 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) describes a 'Change Point' reading, which serves as both a Foresight (for the old instrument position) and a Backsight (for the new instrument position), but the term 'backsight' specifically refers to the reading taken *back* to the known point.
- Option (d) is incorrect as backsights are primary measurements, not specific tools for error correction (though they are used in calculations to check for errors).
What is the key benefit of maintaining a high intensity of irrigation in an area?
A)
Increased agricultural productivity
B)
Reduced water table depletion
C)
Decreased water use
D)
Increased soil erosion
Intensity of irrigation refers to the proportion of the total cultivable area that is irrigated. When the intensity of irrigation is high, it means a larger portion of the land is receiving controlled water supply regardless of the unpredictability of rainfall. This allows for: 1) Multiple cropping (growing more than one crop per year), 2) The cultivation of high-yielding varieties that require consistent water, and 3) Reduction in crop failure due to drought. Consequently, this leads to a significant increase in overall agricultural productivity.
Why other options are incorrect:
- Option b: High intensity of irrigation often leads to increased groundwater extraction (if using tube wells), which typically accelerates water table depletion rather than reducing it.
- Option c: Increasing the intensity of irrigation inherently increases the total volume of water used in the area.
- Option d: While improper irrigation techniques can cause erosion, increased intensity is not intended to increase erosion; erosion is a negative side effect, not a 'benefit'.
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 lines 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 is established, and the elevations of these points are determined. 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
- Radial line method
Comparing the options:
- Option (a) Direct method is a standard technique.
- Option (b) Indirect method is the broad category of techniques.
- Option (d) Grid method is a specific type of indirect contouring.
- Option (c) Compass method is used for measuring directions (bearings) and plotting horizontal layouts (traversing), but it cannot measure elevations (vertical distance), which is the fundamental requirement for contouring. Therefore, it is NOT a technique of contouring.
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 (Correct):** A closed traverse starts and ends at the same point or connects two known points. Because it forms a loop or a closed circuit, it allows the surveyor to calculate the 'closing error' (the difference between the measured and theoretical coordinates). In areas with multiple obstacles, the surveyor can deviate the path of the traverse to bypass these obstacles while still maintaining the ability to check for accuracy and correct errors through balancing. This makes it the most reliable and best-suited method for complex terrains.
2. **Open Traverse:** An open traverse does not return to the starting point or close on a known point. It is used for linear projects like roads or railways. Because there is no closing point, there is no way to check for cumulative errors in measurement, making it unsuitable for areas where obstacles force frequent changes in direction.
3. **Radial Traverse:** This involves taking measurements from a single central point to various surrounding points. It is only effective for small, open areas where the central point has a clear line of sight to all other points. Obstacles would block the line of sight, making this method impractical.
4. **Triangulation:** While highly accurate for large areas, triangulation relies on the measurement of angles in a network of triangles. It requires clear inter-visibility between stations. In an area with multiple obstacles, establishing these clear lines of sight for large triangles is often impossible.
What does Dicken’s formula estimate?
A)
The rainfall intensity
B)
The peak flood discharge in a catchment
C)
The evaporation rate
D)
The infiltration rate
Dickens' formula is an empirical formula used in hydrology to estimate the peak flood discharge (peak runoff) of a catchment area, particularly in regions where rainfall data is scarce. The formula is expressed as Q = C * A^(3/4), where 'Q' is the peak discharge, 'C' is Dickens' constant (which varies based on the region and climate), and 'A' is the catchment area.
Analysis of other options:
- Option (a) Rainfall intensity is typically measured using rain gauges or estimated via Intensity-Duration-Frequency (IDF) curves.
- Option (c) Evaporation rate is measured using evaporation pans or estimated via Penman's equation.
- Option (d) Infiltration rate is measured using infiltrometers or estimated via Horton's equation.
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 rainfall recorded divided by the total duration of the rainfall event.
Given:
- Total Rainfall (P) = 50 mm
- Total Duration (t) = 10 hours
Formula:
Average Intensity (I) = Total Rainfall / Total Duration
I = 50 mm / 10 hours
I = 5 mm/hr
Comparing this result to the options:
- Option (a) 2.5 mm/hr is incorrect (result of 25/10).
- Option (b) 5 mm/hr is correct.
- Option (c) 7.5 mm/hr is incorrect.
- Option (d) 10 mm/hr is incorrect (result of 100/10).
Which of the following irrigation methods is best suited for sandy soil?
A)
Sprinkler irrigation
B)
Drip irrigation
C)
Flood irrigation
D)
Furrow irrigation
Step-by-step reasoning: 1. Analysis of Sandy Soil: Sandy soils have large particles and large pore spaces, leading to high infiltration rates and low water-holding capacity. Water percolates downward very quickly (high permeability). 2. Evaluating Flood and Furrow Irrigation: These are surface irrigation methods. In sandy soil, water sinks rapidly into the ground before it can move laterally to cover the field, leading to massive water wastage and uneven distribution. 3. Evaluating Drip Irrigation: While highly efficient, drip irrigation is primarily used for high-value crops or water-scarce regions. In very sandy soils, the 'wetting bulb' becomes narrow and deep rather than wide, which may require very close emitter spacing to be effective. 4. Evaluating Sprinkler Irrigation: Sprinkler irrigation applies water in a manner similar to rainfall. Because it allows for frequent, light applications of water, it prevents the deep percolation losses associated with surface irrigation. It is specifically recommended for sandy soils because it can match the application rate to the soil's infiltration rate more effectively than surface methods, ensuring the root zone is adequately moistened without wasting water. Therefore, sprinkler irrigation is the most suitable general method for sandy soils.
Why does sandy soil require more frequent irrigation than clayey soil?
A)
Sandy soil has a lower infiltration rate
B)
Sandy soil has a lower water-holding capacity
C)
Clayey soil allows rapid water movement
D)
Clayey soil loses more water due to evaporation
The frequency of irrigation is primarily determined by the soil's ability to retain water against the force of gravity (water-holding capacity).
1. **Sandy Soil:** Composed of large particles with large macropores. While this allows for high infiltration rates, it means the soil cannot hold onto water effectively. Water drains quickly through the profile, leading to a low water-holding capacity. Consequently, the root zone dries out faster, requiring more frequent irrigation.
2. **Clayey Soil:** Composed of very small particles with tiny micropores. These small pores create strong capillary forces that hold water tightly. Therefore, clayey soil has a high water-holding capacity and requires less frequent irrigation.
Analysis of other options:
- Option (a) is incorrect because sandy soil actually has a *higher* infiltration rate than clayey soil.
- Option (c) is incorrect because clayey soil restricts water movement due to low permeability; sandy soil allows rapid movement.
- Option (d) is incorrect because evaporation is more dependent on surface area and climate; clayey soils often retain moisture longer, reducing the relative rate of depletion compared to sandy soils.
Which of the following factors has the most direct and immediate impact on runoff generation?
A)
Land slope
B)
Soil type
C)
Vegetation cover
D)
Rainfall intensity
Runoff generation is primarily governed by the relationship between the rate at which water is supplied to the surface and the rate at which the soil can absorb it (infiltration capacity).
1. **Rainfall Intensity (Correct):** This is the most direct and immediate factor. According to the concept of 'Horton Overland Flow', if the rainfall intensity exceeds the infiltration capacity of the soil, runoff is generated immediately. Even in highly permeable soils, an extremely high rainfall intensity can trigger immediate runoff.
2. **Land Slope (Incorrect):** Slope affects the velocity of runoff and the time it takes to reach a stream, but it is a static physical characteristic. It influences the process but does not 'trigger' the generation of runoff in the same immediate way as a rain event.
3. **Soil Type (Incorrect):** Soil type determines the infiltration capacity (e.g., sandy soil has high infiltration, clay has low). While critical, it is a baseline condition. Runoff only occurs when the rainfall intensity interacts with this capacity.
4. **Vegetation Cover (Incorrect):** Vegetation intercepts rainfall and slows down surface flow, increasing the time available for infiltration. Like soil type, this is a modifying factor rather than the immediate driver of the runoff event.