Design of Sewer Notes | EduRev

Environmental Engineering

Civil Engineering (CE) : Design of Sewer Notes | EduRev

The document Design of Sewer Notes | EduRev is a part of the Civil Engineering (CE) Course Environmental Engineering.
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Hydraulic formulas for Determining Flow Velocities in Sewers and Drains

(i) Chezy’s Formula
Design of Sewer Notes | EduRev
Where,
C = Chezy’s constant
S = Hydraulic gradient
R = Hydraulic mean depth or Hydraulic Radius
Design of Sewer Notes | EduRev
Design of Sewer Notes | EduRev
for circular sewer of dia D (in Running full)
Discharge,
Design of Sewer Notes | EduRev
Where,
A = Flow area of cross-section.
(a) Kutters Formula
Design of Sewer Notes | EduRev
Where,
n = Rugosity coefficient
S = Bed slope
(b) Bazin formula
Design of Sewer Notes | EduRev
Where, k = Bazin constant.
(ii) Manning’s Formula
Design of Sewer Notes | EduRev
(iii) Crimp and Burge’s Formula

Design of Sewer Notes | EduRev

This formula is close to Manning’s formula for all those sewer materials for which,
Design of Sewer Notes | EduRev
(iv) William Hazen’s Formula

Design of Sewer Notes | EduRev
Design of Sewer Notes | EduRev

Shields Expression for Self Cleansing Velocity

Design of Sewer Notes | EduRev
Design of Sewer Notes | EduRevwhere,
f = Friction Factor
n = Porosity
sin θ ~ tan θ - Slope
⇒ θ = tan-1 (Slope)
G = Specific gravity of solid
d = Avg size of solid.
Design of Sewer Notes | EduRev
where, k = (1 - n) sin θ

Hydraulic Characteristics of Circular Sewer Free Board Provision
(i) Depth of partial flow
Design of Sewer Notes | EduRev

Design of Sewer Notes | EduRev

where,
α = Central angle in degree
d = Depth of partial flow
D  Dia of full section
(ii) Proportionate depth, (d/D)
Design of Sewer Notes | EduRev
(iii) Proportionate depth, (a/A)
Design of Sewer Notes | EduRev
Where,
Design of Sewer Notes | EduRev
Design of Sewer Notes | EduRev
(iv) Proportionate perimeter
Design of Sewer Notes | EduRev
Where,
Design of Sewer Notes | EduRev
(v) Proportionate Hydraulic Mean Depth
Design of Sewer Notes | EduRev
(vi) Proportionate Velocity
Design of Sewer Notes | EduRev
(a) If
Design of Sewer Notes | EduRev
(vii) Proportionate Discharge
Design of Sewer Notes | EduRev
(viii) For two sewers whose degree of cleansing is same.

Design of Sewer Notes | EduRev

 i.e.
Design of Sewer Notes | EduRev
(a) Ss/S = R/r
(b) Vs/V = N/n · (r/R)1/6 
(c) qs/Q = N/n ·(a/A) (r/R)1/6 

  • Design of Sewer Notes | EduRev design to run 1/2 full of Q design.
  • Design of Sewer Notes | EduRev design to run 2/3 full of Q design.
  • Design of Sewer Notes | EduRev design to run 3/4 full of design.

where, ϕ Dia of sewer.
Qdesign = 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)
Design of Sewer Notes | EduRev

Estimation of Peak Drainage Discharge
(i)
Design of Sewer Notes | EduRev
Where, k = Runoff/rainoff
Suffix 1,2, … n used for k is runoff of 1,2, ….n.
A = Area.
(ii)
Design of Sewer Notes | EduRev
(iii)

Design of Sewer Notes | EduRev
Where,
Maximum rainfall intensity of a particular frequency having duration equal to time of concentration.
po = (Point rainfall intensity of same frequency as PC) × Area dispersion factor. (cm/hr)
Tc = Time of concentration in hr.
(iv) 

Design of Sewer Notes | EduRev
where,
QP = Peak discharge in m3/sec.
A = Catchment area in (Hectare)
Critical rainfall in (cm/hour)
Design of Sewer Notes | EduRev

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