Test: Irrigation - 1 - Civil Engineering (CE) MCQ

Culturable Cultivated Area is the area in which crop is grown at a particular time or crop season.

Solution: (b) 

Ridge/Watershed Canal: The dividing ridge line between the catchment areas of two streams (drains) is called the watershed or ridge canal. It is suitable for plain areas, where slopes are relatively flat and uniform. This type of alignment ensures gravity irrigation on both sides of the canal.

Contour Canal: Canal aligned nearly parallel to the contour line is called contour canal. They are aligned generally when canals take off from a river. Culturable area lies on one side of it as one of the banks is on the higher side.

Side Slope Canal- A side slope canal is that which is aligned at right angles to contours i.e. along the side slopes. It is a canal which is aligned roughly at right angle to contours of the country but not on the watershed of the valley. The canal thus, runs parallel to the natural drainage of the country and as such cross drainage works are avoided.

• Capacity Control: The capacity of an irrigation canal is usually controlled by the maximum demand for water during a specific period.


• Kor Demand: The term "kor" refers to the peak water requirement of a crop at a specific growth stage. Therefore, the capacity of the canal needs to be able to meet this peak demand to ensure proper irrigation.


• Kharif Crops: Kharif crops are typically sown in the rainy season and have specific water requirements during their growth period. The canal capacity needs to be sufficient to meet the peak demand for these crops.


• Control Factor: The canal capacity is controlled by the kor demand of kharif crops to ensure that there is an adequate supply of water during the critical growth stages of these crops.


• Efficient Irrigation: By controlling the canal capacity based on the kor demand of kharif crops, farmers can ensure efficient irrigation practices and maximize crop yields.

It is the structure required to dispose of surplus or excess water from canal from time to time. Thus, a canal escape serves as safety valve for canal system. It provides protection to the canal from possible damage due to excess supply which may be due to mistake in releasing water at head regulator or heavy rainfall that makes sudden regular demand of water.

Syphon Aqueduct as the Recommended Crossdrainage

- Explanation:
- In the case of a natural drain crossing an irrigation canal, a syphon aqueduct is the most suitable type of crossdrainage to recommend.
- A syphon aqueduct consists of a closed conduit that carries water over the canal without obstructing the flow of water in the canal.
- This type of crossdrainage is ideal for situations where a natural drain needs to pass over an irrigation canal to ensure the smooth flow of water in both the drain and the canal.
- By using a syphon aqueduct, the natural drain can continue its course without causing any interruption to the irrigation canal's operation.

Therefore, based on the specific scenario of a natural drain crossing an irrigation canal, a syphon aqueduct is the most appropriate type of crossdrainage to recommend.

If bed level of canal is sufficiently above the HFL of the drain, an aqueduct is the right choice. Sometimes bed level of canal may be little below the HFL of drain so that water flows under symphonic action. This structure is known as aqueduct siphon. If bed level of the drain is sufficiently above the canal FSL, a super passage may be constructed. If the canal FSL is little above bed level of drain to allow symphonic action, the structure is called Canal Siphon. Aqueduct or super-passage type of drainage works are used when high flood discharge is large and continues for a sufficient time. A level crossing is used when the canal water and drain water are allowed to intermingle with each other. This is adopted when high flood drainage discharge is short lived.

• Statement 1: An aqueduct is a cross drainage work in which a canal is carried over the drainage channel. This statement is correct as an aqueduct is a structure that carries water from one location to another, often over a drainage channel or another obstacle.



• Statement 2: A drainage channel is carried over the canal. This statement is incorrect as in an aqueduct, the canal is typically carried over the drainage channel, not vice versa.



• Statement 3: Both drainage channel and canal are at the same level. This statement is incorrect as in an aqueduct, the canal is usually elevated above the drainage channel to allow the water to flow across.

Therefore, the correct statement is 1 only as mentioned in option A.

Correct Answer is D. The drain flows below the canal in aqueduct and syphon aqueduct, and the drain flows above the canal in super passage and syphon.

• Definition: Manning's formula is commonly used in hydraulic engineering to calculate the flow of water in open channels.


• Parameters: The formula takes into account the channel geometry, roughness coefficient, hydraulic radius, and slope of the channel.


• Accuracy: Manning's formula is widely accepted and provides reasonably accurate results for designing lined alluvial canals.


• Application: It is specifically suitable for designing lined canals where the flow of water needs to be controlled and managed efficiently.


• Advantages: Manning's formula is easy to use, widely available in textbooks and software, and has been extensively validated in practical applications.

Canal lining is the process of reducing seepage loss of irrigation water by adding an impermeable layer to the edges of the trench. Seepage can result in losses of 30 to 50 percent of irrigation water from canals, so adding lining can make irrigation systems more efficient so there is increase in command area.

• Provide safe exit to avoid accidental drowning: Safety ladders are crucial in large irrigation canals to ensure that individuals who accidentally fall into the water have a way to safely exit and avoid drowning.



• Enable the cattle to cross the canal: While safety ladders are primarily for human safety, they can also serve the purpose of allowing cattle or other animals to safely cross the canal without getting stuck or injured.



• Enable the swimmers to get out of the canal: In case of recreational swimming or other water activities in the canal, safety ladders provide swimmers with a means of getting out of the water easily and safely.



• Enable the fish to pass from one place to another: Safety ladders can also facilitate the movement of fish or other aquatic life between different parts of the canal, promoting biodiversity and ecosystem health.

Overall, safety ladders play a crucial role in ensuring the safety of both humans and animals in and around large irrigation canals, making them an essential feature for preventing accidents and promoting the well-being of all living beings in the area.

Advantages of Canal Lining:

An important reason for lining a canal can be the reduction in water losses, as water losses in unlined irrigation canals can be high. Canals that carry from 30 to 150 liters/sec can lose 10 to 15% of this flow by seepage and water consumption by weeds. Lining a canal will not completely eliminate these losses, but roughly 60 to 80% of the water that is lost in unlined irrigation canals can be saved by a hard-surface lining.

• Importance: Under-drainage arrangements in canals are necessary to prevent waterlogging and seepage issues, which can weaken the structure of the canal over time.


• Types of canals: Under-drainage arrangements are required in both unlined canals and lined canals to ensure proper drainage and stability.


• Unlined canals: In unlined canals, under-drainage arrangements help in maintaining the flow of water and prevent erosion of the canal banks due to seepage.


• Lined canals: Even in lined canals, under-drainage arrangements are essential to prevent water seepage under the lining, which can lead to erosion and structural instability.


• Construction on sandy soils: Under-drainage arrangements are especially crucial in lined canals constructed on sandy soils, as sandy soils have higher permeability and are prone to seepage issues.

Therefore, under-drainage arrangements are necessary in both lined and unlined canals to ensure the proper functioning and longevity of the canal structure.

Explanation:

The best alignment of off – taking channel is that in which the off – taking channel makes zero angle with the parent channel initially and then separates out in transition.

The depth of water should always be such that off take channel runs full.

The transitions should be properly designed, so as to avoid accumulation of slit. The transition can also be used as metering flume.

Note:

Thus depth, slope and width will be the correct order of preference of parameters.

• Efficiency: A trapezoidal cross section provides the best balance between minimizing construction costs and maximizing hydraulic efficiency. The wide base of the trapezoid allows for greater water flow capacity compared to a semicircular or triangular cross section.



• Stability: The sloping sides of a trapezoidal canal help in maintaining stability by preventing erosion and slippage of the canal walls. This shape distributes the water flow evenly and reduces the risk of bank collapse.



• Construction: Constructing a trapezoidal canal is relatively easier and cost-effective compared to a semicircular or triangular canal. The shape allows for easier placement of lining materials and maintenance of the canal structure.



• Flow Characteristics: The trapezoidal shape promotes uniform flow distribution and reduces energy losses. This results in efficient water conveyance and ensures proper irrigation and drainage in the canal system.

• Definition of Water-logged Land: A land is said to be water-logged when the soil pores in the root zone get saturated with water, either by the actual water table or by its capillary fringe.


• Factors contributing to water-logging: Water-logging can occur due to various reasons such as poor drainage, high water table, heavy rainfall, or irrigation practices.


• Effects of water-logging: Water-logging can have detrimental effects on plant growth as it reduces the availability of oxygen to plant roots, leading to root rot and ultimately plant death.


• Prevention and management: To prevent water-logging, proper drainage systems should be in place to allow excess water to drain away. Avoid over-irrigation and choose appropriate crops that are tolerant to water-logging conditions.


• Monitoring and remediation: Regular monitoring of soil moisture levels and implementing remedial measures such as installing sub-surface drainage systems can help in managing water-logged lands.

• Ill-aeration of root zone: Water-logging leads to poor aeration of the root zone, causing a lack of oxygen for the plants to thrive. This lack of oxygen can stunt growth and development, ultimately reducing crop yields.



• Growth of water-loving plants: Water-logging creates a favorable environment for the growth of water-loving plants that can compete with the sown crop for essential nutrients and resources. This competition can lead to reduced crop yields as the sown crop may not be able to access the necessary resources for optimal growth.



• Saline water surrounding the root zone: In cases where water-logging leads to the accumulation of saline water around the root zone, it can extract the good water from plant roots through osmosis. This can result in water stress for the plants, affecting their overall health and productivity.

These factors combined contribute to reduced crop yields in water-logged areas, highlighting the importance of proper drainage and water management practices in agriculture.

Explanation: The various factors that contribute to the rise in water table i.e. water-logging are –
• Over and intensive irrigation
• Seepage of water through canals and adjoining high lands
• Inadequate natural drainage and surface drainage
• Excessive rains and submergence due to floods
• Impervious obstruction.

• Good drainage for irrigated land: This is a remedial measure for water logging as proper drainage systems can help in removing excess water from the land, preventing water logging.



• Conjunctive use of water in the basin: This is a remedial measure as it involves managing the use of surface water and groundwater together to prevent water logging and ensure sustainable water management.



• Lining of canals and water courses: This is also a remedial measure as it helps in reducing seepage losses and prevents water logging by maintaining proper flow of water.



• Contour bunding: Contour bunding is not a remedial measure for water logging. It is a soil conservation technique used to prevent soil erosion by slowing down the flow of water on slopes, but it does not directly address the issue of water logging.

• Leaching: Leaching is the process of flushing out excess salts from the soil by applying water. This helps in reducing the pH of alkaline soils.



• Addition of Gypsum to Soil: Gypsum is a common soil amendment that can help in improving soil structure and reducing the alkalinity of the soil. It reacts with sodium in the soil, forming sodium sulfate which can be easily leached out.



• Providing Good Drainage: Ensuring good drainage in alkaline soils can help in preventing waterlogging and reducing the concentration of salts in the soil. This can aid in reclaiming the soil and making it more suitable for plant growth.



• Addition of Gypsum to Soil and Leaching: A combination of adding gypsum to the soil and leaching it with water can be an effective way to reclaim alkaline soils. Gypsum helps in displacing sodium ions and leaching helps in removing the excess salts, thereby improving the soil quality.

By following these methods, alkaline soils can be effectively reclaimed and made suitable for plant growth.

• Dead furrows: Dead furrows are shallow depressions or ditches created in cropped fields to facilitate drainage of excess water.



• Use in drainage: Dead furrows are used as a method of surface drainage to remove excess irrigation or rainwater from the fields.



• Benefits: This method helps in preventing waterlogging, which can lead to root rot and other issues in crops.



• Cost-effective: Using dead furrows for drainage is a cost-effective solution compared to other drainage methods like tile drainage or French drains.



• Environmental impact: Dead furrows also help in reducing soil erosion and nutrient runoff, thus promoting sustainable agriculture practices.

• Salt resistant crop: Barseem is known for its ability to tolerate high levels of salinity in the soil, making it an ideal choice for recently reclaimed alkaline soil.



• Nutrient-rich: Barseem is a nutrient-rich crop that can help improve the fertility of the soil, which is important for newly reclaimed land.



• Growth characteristics: Barseem has a fast growth rate and can quickly establish itself in the soil, providing cover and protection against erosion.



• Soil improvement: Barseem has deep roots that can help break up compacted soil and improve drainage, which is beneficial for alkaline soils.



• Economic benefits: Barseem is a valuable forage crop that can be used for livestock feed, providing an additional source of income for farmers.

Overall, barseem is the best choice for sowing on recently reclaimed alkaline soil due to its salt resistance, nutrient-rich properties, fast growth rate, soil improvement benefits, and economic advantages.

• Using limestone as a soil amendment: Limestone is commonly used to raise pH levels in acidic soils. It contains calcium carbonate, which reacts with the soil to neutralize acidity.


• Application method: Limestone can be applied to the soil either as a ground powder or in a pelletized form. It is usually spread evenly over the soil surface and then incorporated into the soil through tilling or watering.


• Effectiveness: Limestone gradually releases calcium ions into the soil, which helps to raise pH levels over time. It is a long-term solution for reclaiming acidic soils.


• Monitoring: It is important to regularly monitor the pH levels of the soil after applying limestone to ensure that the desired pH range is maintained. Additional applications may be needed depending on the initial soil pH and crop requirements.

Leaching is a process of extracting a substance from a solid material that is dissolved in a liquid. Thisprocess is commonly referred to as extraction, particularly in the chemical industry. Three basic steps are involved in the leaching process: contact, separation, and extraction.