Q1: For a most economical rectangular channel, the width of the channel must be

ANS:B - twice the depth of flow

For a most economical rectangular channel, the width of the channel must be twice the depth of flow. In an economical rectangular channel, the hydraulic radius (or hydraulic mean depth) is maximized when the width is twice the depth of flow. This configuration minimizes the wetted perimeter for a given cross-sectional area, which reduces friction losses and makes the channel more economical to construct and operate. Therefore, the width of the channel should be twice the depth of flow for it to be considered the most economical rectangular channel.