All above and below ground horizontal drainage pipes should be laid to an adequate gradient.
Gradients from 1 in 40 to 1 in 110 will normally give adequate flow velocities.
A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes.
If the gradient is not steep enough i.e. less than 1 in 110, then the pipe could block if the solids slow down and become stranded. The fall in a pipe may be defined as the vertical amount by which the pipe drops over a distance. The distance can be between sections of pipe or between manholes.
A gradient may be defined as fall divided by distance.
GRADIENT = FALL / DISTANCE
For example a 24 meter section of pipework has a fall of 0.30 meters the gradient = 0.30 / 24
gradient = 0.0125
This can be converted into a gradient written as a ratio
gradient = 1 / 0.0125 = 80
gradient = 1 in 80
If the gradient is known then the formula can be rearranged to calculate the fall
FALL = GRADIENT X DISTANCE
For example to calculate the fall in a 50 meters of pipework if the gradient is to be 1 in 80. A gradient of 1 in 80 as a number instead of a ratio is 1 / 80 = 0.0125
Fall = 0.0125 x 50
Fall = 0.625 meters (625 mm)
How we can help?
If you have issues with blocked drains, a soakaway or drainage field that has failed contact us at Tekneka Ltd on 01772 846193 / 07968 143756 or fill in the contact form