The most suitable section of a lined canal is a trapezoidal section with rounded corners. This is because a trapezoidal section provides the most efficient flow of water, while the rounded corners reduce the risk of erosion.
A triangular section with a circular bottom is not as efficient as a trapezoidal section, as it does not provide as much surface area for the water to flow over. This can lead to the water flowing more slowly and potentially causing erosion.
A trapezoidal section with sharp corners is also not as efficient as a trapezoidal section with rounded corners, as the sharp corners can cause the water to flow more turbulently and potentially cause erosion.
Therefore, the most suitable section of a lined canal is a trapezoidal section with rounded corners.