What does 2 percent slope mean in sewer pipe slope?

Answer 1

Liquid will flow down the slope at this gradient without surging and the use of a pump is not needed.

NB

The Roman aquaducts in Europe(France etc.,) have a 2 degree slope. This was to make the water flow, with out surging, and there being no machinery to pump water.

The Archimedean Screw will lift water from a low level to a higher level, but needs the use of a donkey/mule/horse etc., to power rotate the screw.

Answer 2

2 percent slope means a 2 foot vertical change for every 100 feet horizontal distance. So if this was a sewer pipe coming out of your house at ground level, then 100 feet away from your house, it would be 2 feet underground. Percent slope is a non-dimensional term, so you could say 2 meters for every 100 meters as well. This is useful to determine how deep a ditch must be dug, and also how much pipe you will need to buy (since the pipe is the hypotenuse of a triangle, you would need [sqrt(1002 + 22) = 100.02] feet of pipe for every 100 feet horizontal distance. Not much difference but you wouldn't want to run short on a project. More importantly, eventually the drop will be too deep to dig a ditch and a lift station should be installed (a pump which pumps the contents up to a higher level, so that it can start flowing downhill again)

Sometimes you will see signs on a road before a hill (or at the top of a hill) stating 4 percent grade. This has the same meaning (4 foot drop over 100 foot horizontal distance) and is important mainly for truck drivers so that they can apply the brakes accordingly, especially if they are hauling a heavy load, so that the truck doesn't get out of control.