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Chapter:
How is quantity of storm water estimated.
The quantity of storm water is estimated from the following two methods:
- Rational Methods
- Empirical Methods
Rational Method:
In rational method, the storm flow or runoff reaching a sewer is given by the expression :
`Q=(CiA)/360` `m^3`/sec
Where,
Q= storm water flow or runoff (WWF)
C = Runoff coefficient or impermeability factor
I = Intensity of rainfall in mm/hr
A = Area of catchment in hectare
The above formula is known as rational formula. This technique is used for urban areas, generally not exceeding `5\ km^2` in areas. For areas larger than `5\ km^2`, other techniques must be employed.
For determining storm water flow or runoff by rational formula, three factors i.e, catchment area or drainage area, runoff coefficient and intensity of rainfall are required to be determined.
Catchment area:
The catchment or drainage area to be served by a sewer can be dete....
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Similar Question
Explain the factors affecting the source of storm sewage.
How is quantity of storm water estimated.
A certain district of a city has a projected population of 50,000 residing over an area of 40 hectares. Find the design discharge for the sewer line, for the following data :
- Rate of water supply = 200 lpcd
- Average impermeability coefficient for the entire area =0.3
- Time of concentration = 50 minutes
The sewer line is to be designed for a flow equivalent to the wet weather flow (WWF) plus twice the dry weather flow (DWF).Use British ministry of health formula. Assume that `70%` of water supply reaches in the sewer as wastewater.(Ans: `0.648 m^3/s`)
