In canal embankments, what is a counter berm? Choose the most accurate definition used in irrigation engineering practice.

Introduction / Context:
Canal banks (embankments) may suffer from sloughing and instability, especially on the outer slope where seepage and drawdown act. To improve stability and reduce the driving height of the slope, engineers provide counter berms.

Given Data / Assumptions:

• Embanked canal with inner (water side) and outer (country side) slopes.
• Counter berm is an ancillary earthwork used for stability, drainage, and maintenance access.
• No numerical calculation is required; this is a definition/identification task.

Concept / Approach:
A berm is a horizontal bench. A counter berm specifically counteracts slope instability by interrupting the outer slope, shortening the seepage face, and providing a platform to catch minor slips and to drain seepage water safely.

Step-by-Step Solution:
Identify the slope most vulnerable to instability: outside (country) slope.Define a counter berm as a horizontal bench on that outside slope.Conclude that the correct description is a horizontal benching provided on the outside slope.

Verification / Alternative check:
Canal manuals illustrate cross-sections showing the counter berm breaking the outer slope, often combined with toe drains to control seepage.

Why Other Options Are Wrong:

• Inside slope benching is typically called a berm or inspection berm but is not a counter berm.
• “Vertical benching” is self-contradictory; a berm is horizontal.
• “None of these” is incorrect because a standard definition exists.

Common Pitfalls:
Confusing inspection berms on the water side with counter berms; assuming any platform is a counter berm without considering location and purpose.

Final Answer:
a horizontal benching provided on the outside slope