With reference to lining of a canal which of the following statement is/are correct?
i. It is necessary to minimize the seepage loss in canal.
ii. It increases the discharge in the canal section by increasing the velocity.
Select the correct answer using the codes given below :

Question

With reference to lining of a canal which of the following statement is/are correct?

i. It is necessary to minimize the seepage loss in canal.

ii. It increases the discharge in the canal section by increasing the velocity.

Select the correct answer using the codes given below :

Prepp Team · Accepted Answer

Understanding the Benefits of Canal Lining

Canal lining is a process of covering the bed and sides of an irrigation canal with an impermeable layer. This lining can be made of various materials such as concrete, bricks, asphalt, compacted clay, or even plastic films. The primary purpose of lining a canal is to improve its performance and efficiency.

Analysis of Statement i: Minimizing Seepage Loss in Canals

Statement i says that canal lining is necessary to minimize the seepage loss in a canal. Seepage loss refers to the water that leaks out of the canal through its bed and banks into the surrounding soil. This loss can be significant, especially in canals built through porous or permeable soils. Seepage reduces the amount of water delivered to the fields, leading to water wastage and potentially waterlogging issues in adjacent areas.

An unlined canal allows water to infiltrate into the ground.
Canal lining creates a barrier that is relatively impermeable.
This impermeable layer significantly reduces or prevents water from seeping out.

Therefore, lining a canal directly addresses and minimizes seepage loss, conserving water and improving irrigation efficiency. Statement i is correct.

Analysis of Statement ii: Increasing Discharge by Increasing Velocity

Statement ii claims that canal lining increases the discharge in the canal section by increasing the velocity. The flow velocity in a canal is influenced by factors like the channel's slope, hydraulic radius (ratio of cross-sectional area to wetted perimeter), and the roughness of the canal surface. The roughness is often represented by Manning's roughness coefficient ('n').

Unlined canals, especially those with natural earth surfaces, are rough.
This roughness creates friction between the water and the canal surface, slowing down the flow.
Lining materials like concrete, brick, or smooth plastic have a much lower roughness coefficient ('n') compared to earth.
A smoother surface reduces friction, allowing water to flow faster for the same slope and hydraulic radius.

Discharge (Q) in a canal is calculated using the formula:

\( Q = A \times v \)

where \( A \) is the cross-sectional area of flow and \( v \) is the average velocity of flow.

If the cross-sectional area \( A \) remains the same (or changes minimally), an increase in velocity \( v \) directly leads to an increase in discharge \( Q \). Since lining increases velocity by reducing friction, it also increases the discharge capacity of the canal section.

Therefore, canal lining increases discharge by increasing the flow velocity. Statement ii is correct.

Conclusion on Canal Lining Statements

Based on the analysis of both statements:

Statement i: Canal lining minimizes seepage loss. (Correct)
Statement ii: Canal lining increases discharge by increasing velocity. (Correct)

Both statements accurately describe significant benefits of canal lining.

Thus, the correct answer is that both statement i and statement ii are correct.

Revision Table: Canal Lining Benefits

Statement	Description	Effect of Canal Lining
i	Minimizing seepage loss	Correct. Lining creates an impermeable barrier, stopping water from leaking into the ground.
ii	Increasing discharge by increasing velocity	Correct. Lining smoothens the surface (reduces friction), increasing flow velocity, which in turn increases discharge.

Additional Information on Canal Lining

Beyond reducing seepage and increasing capacity, canal lining offers several other advantages in irrigation engineering:

Prevents Weed Growth: Lined surfaces inhibit the growth of aquatic weeds in the canal, which can obstruct flow and require costly removal.
Reduces Maintenance Costs: Lined canals are less prone to erosion of banks and bed, reducing the need for frequent repairs and desilting compared to unlined canals.
Increases Command Area: By conserving water and increasing capacity, lining allows for a larger area to be irrigated effectively.
Prevents Waterlogging: Reduced seepage also lowers the groundwater table near the canal, preventing waterlogging of adjacent agricultural lands.
Increces Stability: Lining helps stabilize the canal banks, preventing breaches and structural failures.

While the initial cost of lining can be high, the long-term benefits in terms of water saving, increased efficiency, and reduced maintenance often justify the investment in modern irrigation systems.