Canal Lining Purposes Explained

Canal lining is a construction technique used to cover the bed and sides of an irrigation canal with an impermeable or low-permeability material. This is done to improve the performance and efficiency of the canal system.

The primary goals of providing canal lining include:

• Seepage Control: One of the main reasons for lining canals is to prevent water from leaking out of the canal bed and sides into the surrounding soil. This loss of water through seepage can be significant, especially in permeable soils. Lining helps in greatly reducing or eliminating this seepage.
• Improve Conveying Efficiency: By preventing seepage loss, more water is delivered to the intended destination, improving the overall efficiency of the water conveyance system. Also, a lined channel typically has a smoother surface than an unlined one, which reduces resistance to flow and allows water to move faster, increasing the flow velocity for a given slope and cross-section. This improves the hydraulic efficiency.
• Increase Channel Capacity: Due to reduced resistance and potentially increased flow velocity, a lined channel can carry more water than an unlined channel of the same dimensions and slope. Alternatively, the same amount of water can be carried in a smaller cross-section, which saves land. This effectively increases the conveying capacity.
• Prevent Waterlogging: By controlling seepage, canal lining helps prevent the rise of the water table in adjacent lands, thereby reducing the risk of waterlogging, which can damage crops and infrastructure.
• Reduce Maintenance Costs: Lined canals are less susceptible to erosion and weed growth compared to unlined channels, leading to lower maintenance requirements and costs over time.

Considering the purposes listed above, let's look at the options provided:

• Improve conveying efficiency: As discussed, lining reduces resistance and seepage, both contributing to improved efficiency.
• Increase channel capacity: Lining can increase flow velocity and reduce required area, thus increasing capacity.
• Seepage control: This is a primary purpose of canal lining.
• Increase groundwater recharge: Canal lining prevents water from seeping into the ground. Seepage is the process by which water from the canal recharges the groundwater. Therefore, preventing seepage inherently reduces or stops the groundwater recharge that would otherwise occur from the canal itself. Increasing groundwater recharge is thus NOT a purpose of providing canal lining; in fact, it has the opposite effect from the canal's perspective.

Therefore, increasing groundwater recharge is not a purpose of providing canal lining.