Q1: For a most economical trapezoidal open channel, the half of the top width must be equal to

ANS:B - one sloping side

For a most economical trapezoidal open channel, the half of the top width must be equal to the depth of flow. In an open channel flow, the most economical section is the one that minimizes the construction cost for a given discharge. In a trapezoidal channel, the top width, depth of flow, and side slopes play crucial roles in determining its efficiency and cost-effectiveness. The half of the top width represents the distance from the centerline to one side of the top width. It is a critical parameter in defining the geometry of the trapezoidal channel. For the most economical design, the half of the top width should be equal to the depth of flow. This relationship ensures optimal flow characteristics while minimizing construction costs. It allows for efficient conveyance of water while avoiding excessive excavation or embankment. Therefore, the correct statement is: For a most economical trapezoidal open channel, the half of the top width must be equal to the depth of flow.