City Sanitation Plan, Uttarakhand Detailed Plan report, Muni Ki Reti 1

City Sanitation Plan, Uttarakhand
b. Time of Concentration
The time of concentration is the time allowed for water to reach at the head of the section of the
drain. In general this has to be taken as 30 minutes except while the drain is very close by in which
case it should be taken as 20 minutes. This includes 15 minutes time within the house premises. The
time required in the drain is calculated with the velocity of 1m per second.
The intensity of rainfall for calculating the runoff for any area is then taken from the curve such that
the duration of rainfall for calculating the runoff for any area is then taken from the curve such that
the duration of rainfall is equivalent to the time of concentration for such storm will produce the
maximum runoff in that area. The intensity I for any particular time of concentration is different period
of concurrence. Normally a rainfall with period of occurrence as once in two year is taken for design
until unless some specific site conditions required it otherwise.
2. Flow Formula
The velocity in the storm water drain is calculated in the basis of Chezy‟s Formula.
V= 1/ n (R) 2/3 X (S) 1/2
Where V= mean velocity in meter per second
R= Mean Hydraulic radius
S= Slope of hydraulic gradient
n= Coefficient of roughness
n is Co-efficient whose value is given as below:-
A. Brick Work
Well laid brick work = 0.013
Average brick work = 0.015
Rough brick work = 0.017
Detailed Plan report, Muni Ki Reti
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