Counter berm is necessary to keep the saturation line in a canal embankment well within the toe. A counter berm is an additional horizontal strip of soil or material that is placed on the outer side of the embankment at the toe. It acts as a barrier to prevent water from seeping into the embankment and causing saturation.

Explanation:

What is a saturation line?
The saturation line is the level up to which water can rise in the soil before it starts to flow out. In the case of a canal embankment, the saturation line should be well within the toe of the embankment to prevent any seepage or failure.

Why is seepage a concern?
Seepage is the flow of water through the soil, and it can cause a significant reduction in the strength and stability of the embankment. If the saturation line is too close to or above the toe of the embankment, seepage can occur, leading to the loss of soil particles and potential failure of the embankment.

What is a counter berm?
A counter berm is a raised strip of soil or material placed on the outer side of the embankment, parallel to the toe. It serves as an additional barrier to prevent seepage and keep the saturation line well within the toe.

How does a counter berm help?
By providing a counter berm, the distance between the saturation line and the toe of the embankment is increased. This additional distance acts as a safety factor, reducing the risk of seepage and maintaining the stability of the embankment.

Other measures to prevent saturation line from reaching the toe:
In addition to a counter berm, there are other measures that can be taken to prevent the saturation line from reaching the toe of the embankment:

1. Proper compaction of the embankment material to minimize voids and increase its resistance to seepage.
2. Use of impermeable membranes or geotextiles to increase the barrier effect and reduce seepage.
3. Installation of drainage systems such as weep holes or toe drains to collect and divert any seepage away from the embankment.
4. Regular inspection and maintenance of the embankment to identify and address any signs of seepage or instability.

In conclusion, a counter berm is necessary to keep the saturation line in a canal embankment well within the toe. It acts as an additional barrier to prevent seepage and maintain the stability of the embankment.