ANS:B - bottom side

1. Top side: The top side of sewers typically experiences less scouring compared to the bottom side. Since sewage flows primarily along the bottom of the sewer, the top side is less exposed to the direct hydraulic forces and abrasive action of the wastewater. However, in some cases, turbulence or high flow conditions may cause some degree of scouring on the top side, especially near junctions or bends in the sewer system.
2. Bottom side: The bottom side of sewers is most susceptible to scouring. As wastewater flows through the sewer, it exerts hydraulic pressure and frictional forces on the bottom surface. The continuous flow of sewage, especially during peak flow periods, can lead to erosion of the sewer bed and walls. This erosion can compromise the structural integrity of the sewer and may lead to issues such as pipe degradation, sediment deposition, and even sewer collapses.
3. Horizontal side: The horizontal sides of sewers, meaning the walls or sides parallel to the flow direction, also experience some level of scouring. While the effects may not be as severe as those on the bottom side, turbulent flow conditions or changes in the sewer geometry can contribute to erosion along the horizontal sides. However, compared to the bottom side, the horizontal sides typically experience less scouring due to the reduced hydraulic pressure exerted by the flow.
4. All sides: While the bottom side of sewers is most susceptible to scouring, all sides of the sewer may experience some degree of erosion over time. The severity of scouring depends on factors such as flow velocity, turbulence, sewer material, and the presence of debris or abrasive particles in the wastewater. In some cases, proper sewer maintenance practices and erosion control measures may be necessary to mitigate the effects of scouring on all sides of the sewer and ensure the long-term integrity of the system.

In sewers, the effect of scouring is typically more pronounced on the bottom side. Scouring refers to the erosion or wearing away of the sewer bed and walls due to the flow of wastewater and solids. The bottom of the sewer is particularly susceptible to scouring because it experiences the direct impact of flowing sewage, which can contain abrasive particles and debris. As wastewater flows through the sewer, it exerts a significant amount of hydraulic force on the bottom surface, causing erosion over time. Additionally, turbulence and changes in flow velocity near the bottom of the sewer can further exacerbate scouring effects. While scouring may also occur on the sides of the sewer, the bottom surface is usually more susceptible due to its direct exposure to the flow of wastewater. Therefore, the effect of scouring is generally more prominent on the bottom side of sewers.