Q1: For most economical rectangular section of a channel, the depth is kept

ANS:C - half the width

For the most economical rectangular section of a channel, the depth is typically kept half the width. The concept of an "economical" section in hydraulic engineering refers to achieving the desired flow capacity with the least material, which often translates to the least excavation cost or the most efficient use of materials. In the case of rectangular channels, a depth that is half the width often provides the most economical section. This is because such a proportion allows for sufficient hydraulic capacity while minimizing the amount of material required to construct the channel. While other proportions may also be used depending on specific hydraulic requirements and constraints, keeping the depth half the width is a common and practical guideline for achieving an economical design for rectangular channels. Therefore, the depth being half the width is a typical consideration for the most economical rectangular section of a channel.