Use of nomograms in accordance with IS 1742 to ascertain the gradient, diameter, discharge, and velocity’s unknown values.
In order to determine the necessary gradients, the provided self-cleansing velocities, and the estimated discharge, calculations must be made for each sewage line in a town’s sewerage system. This requires using a formula for each calculation, which makes designing the entire system a laborious task. The use of tables, nomograms, partial flow diagrams, etc. created using the appropriate formula simplifies this process.
The nomogram is frequently employed in sewer system planning. Based on Manning’s method, this nomogram uses 0.013 as the value of n. The Nomogram’s values are based on full, flowing sewers. The Nomogram can be used easily in accordance with IS 1742. A line is formed connecting these two numbers, for instance, if the required discharge of a sewer with n=0.013 is 224 lit/sec and the grade is 0.00125. The matching values are determined by where this line on the velocity scale and diameter scale intersect. Thus, for this case, the sewer’s diameter is determined to be 600 mm, and the required velocity is 0.765 m/sec. Therefore, if two numbers are known, the other two values can be obtained with ease.
Sewers are underground, closed channels used to transport waste from public and residential water closets as well as chemically mixed industrial water without causing a nuisance outside of the community. Sewer cross sections should be designed so that self-cleaning velocity develops even in dry weather flow. No deposit should under no circumstances should you lie down in the sewer bed. These ought to be spread out in the town at a slope that prevents water from manholes in the event of a river flood near the outflow and lead to unhygienic environments.
