In canal engineering, why are finally formed berms provided along the banks of a lined or unlined canal? Select the most complete purpose from the list.

Introduction / Context:
Canal berms are horizontal or gently sloping shelves left between the water edge and the outer embankment. In design and maintenance of irrigation canals, berms serve several hydraulic and geotechnical functions. This question tests understanding of their comprehensive role rather than a single-purpose view.

Given Data / Assumptions:

• Berms are formed after the final trimming or consolidation of canal slopes.
• Canal banks experience hydraulic actions (waves, drawdown) and geotechnical stresses.
• Seepage through embankments must be controlled to avoid piping and instability.

Concept / Approach:

A well-designed berm reduces wave run-up, shortens the seepage path, and provides a buttress that improves slope stability. It also facilitates inspection and maintenance. Effective canal design integrates all these roles rather than isolating a single benefit.

Step-by-Step Solution:

Verification / Alternative check:

Canal manuals prescribe berms in reaches with wind fetch, pervious banks, or higher embankments; field experience shows reduced maintenance where berms exist.

Why Other Options Are Wrong:

Options (a), (b), and (c) are each partially true but incomplete; focusing on only one omits other key functions. Option (e) underplays the hydraulic and geotechnical roles.

Common Pitfalls:

Assuming berms are only for patrol roads; ignoring their effect on phreatic line and wave attack.

Final Answer:

All of the above