Design of Sewer Study Notes for GATE & Civil Engineering Exams
By BYJU'S Exam Prep
Updated on: September 25th, 2023
Design of Sewer
Hydraulic formulas for Determining Flow Velocities in Sewers and Drains
(i) Chezy’s Formula
Where,
C = Chezy’s constant
S = Hydraulic gradient
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
Table of content
Design of Sewer
Hydraulic formulas for Determining Flow Velocities in Sewers and Drains
(i) Chezy’s Formula
Where,
C = Chezy’s constant
S = Hydraulic gradient
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)
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