Q1: A circular sewer section is preferred to because

ANS:D - all the above.

1. It is cheaper in construction: Circular sewer sections are often cheaper to construct compared to other shapes, such as rectangular or egg-shaped sewers. This is because circular sections require less material for the same hydraulic capacity. Additionally, circular sections are easier to install and require fewer support structures, reducing labor and construction costs.
2. It provides maximum area for a given perimeter: Among all possible geometric shapes, a circle provides the maximum area for a given perimeter. This is a geometric property known as the "isoperimetric inequality." In the context of sewer design, maximizing the area of the sewer cross-section relative to the perimeter helps to optimize the flow capacity and efficiency of the sewer system.
3. It provides maximum hydraulic mean depth: Hydraulic mean depth (HMD) is a key parameter used to assess the hydraulic efficiency of a sewer. It is defined as the ratio of the cross-sectional area to the wetted perimeter. In circular sewers, the hydraulic mean depth is maximized compared to other shapes with the same cross-sectional area. This maximization of hydraulic mean depth results in more efficient flow, reduced energy losses, and improved self-cleaning properties of the sewer.