Design a sewer to serve a population of 36000; daily per capita water supply allowance being 135 liters, of which 80% finds its way into sewer. The slope available for the sewer to be laid is 1 in 625 and the sewer should be designed to carry four times the dry weather flow when running full. What would be the velocity of flow in the sewer when running full? Assume n=0.012 in manning�??s formula.

Solution:

Here, the design discharge is,

`Q=(0.8**0.135**36000**4)/86400`

`=0.18\ m^3/s`

From Mannings Formula,

`0.18=1/0.012 **(pi D^2)/4(D/4)^(2/3)**(1/625)^(1/2)`

or, `D=0.518\ m`

Now, the velocity is,

`V=0.18/((pi**0.518^2)/4)`

`=0.85\ m/s`

Solution:

Here, the design discharge is,

`Q=(0.8**0.135**36000**4)/86400`

`=0.18\ m^3/s`

From Mannings Formula,

`0.18=1/0.012 **(pi D^2)/4(D/4)^(2/3)**(1/625)^(1/2)`

or, `D=0.518\ m`

Now, the velocity is,

`V=0.18/((pi**0.518^2)/4)`

`=0.85\ m/s`