Q1: If the diameter of a sewer is 150 mm, the gradient required for generating self cleansing velocity, is

ANS:B - 1 in 100

A gradient of "1 in 100" indicates that for every 100 units of horizontal distance, the elevation changes by 1 unit. In the context of sewer design and hydraulic engineering, gradients are essential for ensuring proper flow velocities within sewer pipes. A gradient of "1 in 100" means a gentler slope compared to "1 in 60" or "1 in 120". For sewer systems, the gradient is crucial for achieving self-cleansing velocities. A self-cleansing velocity is the minimum flow velocity required to prevent solids from settling or accumulating within the sewer pipe. While a gradient of "1 in 100" may not generate as high flow velocities as steeper gradients, it still allows for adequate flow to transport sewage and prevent blockages or sedimentation. In practice, the choice of gradient depends on various factors including the diameter of the sewer pipe, the anticipated flow rates, and the topography of the area where the sewer is installed. Therefore, a gradient of "1 in 100" may be selected in situations where a balance between flow capacity and construction feasibility is desired.