(i) Chezy’s Formula
Where,
C = Chezy’s constant
S = Hydraulic gradient
R = Hydraulic mean depth or Hydraulic Radius
for circular sewer of dia D (in Running full)
Discharge,
Where,
A = Flow area of crosssection.
(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
where,
f = Friction Factor
n = Porosity
sin θ ~ tan θ  Slope
⇒ θ = tan^{1} (Slope)
G = Specific gravity of solid
d = Avg size of solid.
where, k = (1  n) sin θ
Hydraulic Characteristics of Circular Sewer Free Board Provision
(i) Depth of partial flow
where,
α = Central angle in degree
d = Depth of partial flow
D Dia of full section
(ii) Proportionate depth, (d/D)
(iii) Proportionate depth, (a/A)
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) Ss/S = R/r
(b) V_{s}/V = N/n · (r/R)^{1/6}
(c) qs/Q = N/n ·(a/A) (r/R)^{1/6}
where, ϕ Dia of sewer.
Q_{design }=_{ }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.
p_{o} = (Point rainfall intensity of same frequency as P_{C}) × Area dispersion factor. (cm/hr)
T_{c} = Time of concentration in hr.
(iv)
where,
QP = Peak discharge in m^{3}/sec.
A = Catchment area in (Hectare)
Critical rainfall in (cm/hour)
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