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Design-of-sewers-Tutorial

A one meter diameter sewer is required to flow at 60% depth on a grade ensuring a degree of self cleansing equivalent to that obtained at full depth at a velocity of 0.9 m/s. Find required grade, associated velocities and rates of discharged at full depth and 0.6 depth. Take a uniform value of n=0.012 at all depth of flow.

Solution:

For the sewer running at full depth,

`v=0.9=1/0.012 **(1/4)^(2/3)**(S)^(1/2)`

Solving this, we get,

`S=1/1350`

and the discharge is, `Q=(pi **1^2)/4**0.9=0.706\ m^3/s`

Again for the sewer running at partial depth,

`d/D=0.6`

or, `1/2(1-cos (theta/2))=0.6`

or, `theta=203.07^0`

Now, `v/0.9=(1-(360 sin theta)/(2 pi theta))^(2/3)=1.072`

or, `v=0.965\ m/s`

and the discharge is,

`q/0.706=theta/360(1-(360 sin theta)/(2 pi theta))^(5/3)`

or, `q=0.474\ m^3/s`

For the sewer at 60% depth to ensure equivalent self cleansing velocity to that obtained at full depth, it should have gradient `S_s`

`S_s=(R/r)S=1/1499.3`

Now,

`V_s/V=n/n_d(r/R)^(1/6)=1.017`

or, `V_s=0.9305\ m/s`

Again,

`q_s/Q=n/n_d**a_s/A**(r/R)^(1/6)=0.718`

or, `q_s=0.5069\ m^3....

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A one meter diameter sewer is required to flow at 60% depth on a grade ensuring a degree of self cleansing equivalent to that obtained at full depth at a velocity of 0.9 m/s. Find required grade, associated velocities and rates of discharged at full depth and 0.6 depth. Take a uniform value of n=0.012 at all depth of flow.

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A one meter diameter sewer is required to flow at 60% depth on a grade ensuring a degree of self cleansing equivalent to that obtained at full depth at a velocity of 0.9 m/s. Find the required grade

associated velocities and rates of discharged at full depth and 0.6 depth. Take a uniform value of n=0.012 at all depth of flow.

Design of sewers Tutorial

Sanitary-Engineering