The suitable cross-section of sewers to carry combined flow, is

ANS:B - egg shaped

The suitable cross-section of sewers to carry combined flow (both sanitary sewage and stormwater) often depends on various factors including flow characteristics, sediment transport, self-cleaning ability, and hydraulic efficiency. Among the options provided:

• Circular: Circular sewers are commonly used for combined flow because they provide good hydraulic performance, self-cleaning action due to the circular shape, and efficient flow conveyance. They are particularly effective in transporting both sanitary sewage and stormwater.
• Egg shaped: Egg-shaped sewers are also used for combined flow. They offer advantages such as self-cleaning ability, improved sediment transport, and reduced flow velocity during low-flow conditions. However, they may be more costly to construct compared to circular sewers.
• Rectangular: Rectangular sewers are less common for combined flow but can be suitable in certain situations, such as in urban areas with limited space for sewer installation. They may provide good flow capacity but may require more maintenance to prevent sediment accumulation.
• Horse shoe shaped: Horse shoe-shaped sewers, or semi-circular sewers, are sometimes used for combined flow. They offer advantages similar to circular sewers in terms of hydraulic efficiency and self-cleaning ability.

Overall, while all of these cross-section shapes have been used for combined flow sewers, circular and egg-shaped sewers are often considered the most suitable due to their hydraulic performance, self-cleaning ability, and efficiency in transporting both sanitary sewage and stormwater. Therefore, both circular and egg-shaped sewers are commonly used choices for combined flow systems.