Understanding the Sarda Type Fall and Canal Design

Canal falls are structures built across a canal to lower its water level. This becomes necessary when the natural ground slope is steeper than the required bed slope of the canal. Instead of digging a very deep trench to maintain the gentle canal slope over a steep ground, engineers construct falls at intervals to step down the water level.

There are various types of canal falls, each designed with specific objectives and suitable for different site conditions. The question asks about the primary design objective of the Sarda type fall.

The Sarda type fall is a specific design of a vertical drop fall, commonly used in India. It was developed considering specific site conditions and requirements. One of the key challenges in canal alignment is dealing with varying ground levels and ensuring the canal bed remains at a manageable depth. Excessive depth of cutting (digging into the ground) is undesirable because:

• It increases construction costs significantly.
• It requires more land width for the canal section.
• It can lead to stability issues for the canal banks.

The design of the Sarda type fall, by concentrating the drop at specific points, helps in adjusting the canal's longitudinal section to follow the ground slope more closely between the falls. This adjustment allows the canal bed level to be kept relatively high compared to the ground level in certain sections, thereby reducing the amount of earthwork needed for excavation.

Specifically, the Sarda type fall is designed to step down the water level efficiently, allowing the canal bed to be maintained at a higher elevation relative to the surrounding ground level over long stretches. This design characteristic directly contributes to reducing the need for deep excavation or cutting.

Let's look at the options provided:

• Minimise the depth of cutting: As discussed, the primary benefit of using falls, and specifically the Sarda type fall in certain contexts, is to manage the canal bed profile in such a way that deep excavation is avoided.
• Maximise the depth of cutting: This is the opposite of the intended purpose. Maximising cutting depth would increase costs and complexity.
• Maintain the depth of cutting: While the depth of cutting between falls might be relatively consistent if the ground slope is uniform, the purpose of the fall itself is not to maintain a *certain* depth but rather to enable a design that *reduces* the *overall* or *maximum* required depth of cutting compared to a scenario without falls on steep ground.
• Have no relation with depth of cutting: Canal falls are inherently related to the canal's longitudinal profile and how it interacts with the ground slope, which directly impacts the required depth of cutting or height of filling.

Therefore, the design of the Sarda type fall is aimed at facilitating canal alignment that requires less excavation, meaning it helps to minimise the depth of cutting.

Revision Table: Sarda Type Fall Purpose

Additional Information on Canal Design and Falls

When designing a canal system, engineers consider several factors, including the topography of the land, the required flow rate, the available materials, and cost. Canal falls are crucial elements in canal systems constructed on sloping ground.

Without falls, maintaining the required gentle slope of the canal bed over steep ground would necessitate increasingly deep cuts as the canal progresses downhill. This is often uneconomical and structurally challenging. By introducing falls, the canal bed can be stepped down at discrete points, allowing the canal to follow the general ground slope more closely between the falls. This strategy directly reduces the maximum required depth of excavation.

Different types of falls have evolved to handle various drop heights and flow conditions while managing energy dissipation to prevent erosion downstream. The Sarda type fall is known for its simplicity and effectiveness in achieving the goal of reducing excavation depth in suitable terrain.