A certain district of a city has a projected population of 50,000 residing over an area of 40 hectares. Find design discharge for sewer line, for following data :

• Rate of water supply = 200 lpcd
• Average impermeability coefficient for entire area =0.3 
• Time of concentration = 50 minutes 

The sewer line is to be designed for a flow equivalent to wet wear flow (WWF) plus twice dry wear flow (DWF).Use British ministry of health formula. Assume that `70%` of water supply reaches in sewer as wastewater.(Ans: `0.648 m^3/s`) 

Solution:

Given,

Population = 50,000

Area = 40 ha.

Peak factor = 2

Rate of water supply = 200 lpcd

Avg. impermeability factor = 0.3

Time of concentration = 50 min

Now,

The discharge of DWF is,

`Q_(DWF)=(2**0.7**50000**200)/(1000**86400)`

`=0.1620 m^2/s`

Again,

Intensity of rainfall is given by,

`i=1020/(t+20)=1020/70=14.5714` mm/hr

Now, the storm water flow rate is,

`Q_(WWF)=(CiA)/360`

`=(0.3**14.5714**40)/360`

`=0.4857 m^3/s`

Thus, the combined design discharge is,

`Q=Q_(DWF)+Q_(WWF)`

`=0.1620 + 0.4857`

`=0.6477 m^3/s`

Solution:

Given,

Population = 50,000

Area = 40 ha.

Peak factor = 2

Rate of water supply = 200 lpcd

Avg. impermeability factor = 0.3

Time of concentration = 50 min

Now,

The discharge of DWF is,

`Q_(DWF)=(2**0.7**50000**200)/(1000**86400)`

`=0.1620 m^2/s`

Again,

Intensity of rainfall is given by,

`i=1020/(t+20)=1020/70=14.5714` mm/hr

Now, the storm water flow rate is,

`Q_(WWF)=(CiA)/360`

`=(0.3**14.5714**40)/360`

`=0.4857 m^3/s`

Thus, the combined design discharge is,

`Q=Q_(DWF)+Q_(WWF)`

`=0.1620 + 0.4857`

`=0.6477 m^3/s`