Test: Design of Sewer- 1

The circular section has uniform curvature, so it offers less opportunities for deposits.

A circular section of sewer gives a maximum area for a given perimeter and gives the greatest hydraulic mean depth when running full or half.

The wetted perimeter of a circular section of sewer running full is (22/7) *D where D is the internal diameter of circular sewer.

The hydraulic mean depth, R = Area of cross section / Wetted perimeter
= ((22/7) *D²/4) / (22/7) *D
= D/4.

Depth of flow d = (D/2) * (1-cosK/2)
Proportional depth = Depth of flow d / Diameter of section D = (D/2) * (1-cosK/2) / D
= (1/2) * (1-cosK/2).

 Proportional perimeter of a circular sewer running partially half =
(22/7) *D*K/360^o / ((22/7) *D) = K/360^o.

When the diameter of the sewer is up to 0.4m, they are designed to flow at 1/2 depth.

When the diameter of the sewer is between 0.4m and 0.8m, they are designed to flow at 2/3 depth.

Hydraulic mean depth, R = D/4 = 0.4/4 = 0.1m
Slope of sewer S = 1/100, velocity V = 1m/Sec
According to Chezy’s formula, V = C (RS) ^1/2 = C* (0.1/90) ^1/2 = C/30
C = V*30 = 2*30 = 60.

Sewers are the pipelines to carry sanitary sewage and storm water to treatment plants or centres. The process of connecting pipelines and sewer appurtenances to transport waste to sewage treatment plants is called sewage construction.