# Design of Sewer Study Notes for GATE & Civil Engineering Exams

By Vishwajeet Sinha|Updated : January 15th, 2017

Design of Sewer

Hydraulic formulas for Determining Flow Velocities in Sewers and Drains

(i) Chezy’s Formula Where,

C = Chezy’s constant

R = Hydraulic mean depth or Hydraulic Raidus  for circular sewer of dia D (in Running full)

Discharge, Where,

A = Flow area of cross-section.

(a) Kutters Formula Where,

n = Rugosity coefficient

S = Bed slope

(b) Bazin formula Where, k = Bazin constant.

(ii) Manning’s Formula (iii) Crimp and Burge’s Formula This formula is close to Manning’s formula for all those sewer materials for which, (iv) William Hazen’s Formula  SHIELDS EXPRESSION FOR SELF CLEANSING VELOCITY  where,

f = Friction Factor

n = Porosity G = Specific gravity of solid

d = Avg size of solid. where, Hydraulic Characteristics of Circular Sewer Free Board Provision

(i) Depth of partial flow  where, Central angle in degree Depth of partial flow Dia of full section

(ii) Proportionate depth,  (iii) Proportionate area  Where,  (iv) Proportionate perimeter Where, (v) Proportionate Hydraulic Mean Depth (vi) Proportionate Velocity (a) If (vii) Proportionate Discharge (viii) For two sewers whose degree of cleansing is same. i.e. (a) (b) (c) · design to run full of Q design.

· design to run full of Q design.

· design to run full of design.

where, Dia of sewer. Design discharge.

Sewer is designed for Maximum Hourly Discharge

(i) Maximum hourly discharge

= 1.5 (Maximum daily discharge)

(ii) Maximum daily discharge

= 2.0 (Avg daily discharge)

(iii) Maximum hourly discharge

= 3.0 (Avg daily discharge) · Estimation of Peak Drainage Discharge

(i) Where, k = Runoff/rainoff

Suffix 1,2, … n used for k is runoff of 1,2, ….n.

A = Area.

(ii) (iii) Where, Maximum rainfall intensity of a particular frequency having duration equal to time of concentration. (Point rainfall intensity of same frequency as PC) × Area dispersion factor. (cm/hr) Time of concentration in hr.

(iv) where,

QP = Peak discharge in m3/sec.

A = Catchment area in (Hectare) Critical rainfall in (cm/hour) Posted by: Member since Jun 2016 GradeStack Learning Pvt. Ltd.Windsor IT Park, Tower - A, 2nd Floor, Sector 125, Noida, Uttar Pradesh 201303 help@byjusexamprep.com