how to compute the elevation of sewerline?

Answer 1

1/8" per foot is minimum pitch for 4" pipe, although it can be steeper. This is a general answer.

Answer 2

First you need to determine material of the pipe and then determine the pitch which will permit proper discharge. The diameter of your house sewer pipe should be checked with local authorities. Generally it should be 4" diameter if iron is used and 6" if clay pipe is selected.
To determine the pitch, you must know the lowest depth of the house sewer and the depth of the main sewer. Since these two points are to be connected, you must be sure your house sewer outlet is sufficiently higher than the other to insure a pitch that will enable waste water to drain out by gravity. The generally accepted minimum pitch is 1/4" per foot. The pitch may exceed this figure over-all, but the best procedure is to let the house sewer have the minimum pitch from the main sewer connection to the curb; then add additional grade through the use of 1/8 bends until a height is reached sufficient to provide the 1/4-inch grade from that point to the house drain.
A 1/4"-grade is approximately the same as a rise, or fall, of 2 feet in a horizontal distance of 100 feet. You can dig the trench for the sewer at this pitch by the following method. Stretch a level line from the building at the point where the sewer will leave it to the point where the sewer will connect with the main or septic tank. Attach this line to a stake at either end to hold it above ground and use a level to get it horizontal. Then lower the end of the line at the main the necessary distance to get the proper pitch. For a horizontal run of 100 feet, lower it 2 feet; for a run of 50 feet, lower it I foot; for 25 feet, lower it 6"; and so on. Cut a measuring stick to a length equal to the distance from the level line, to the bottom of the drain where it leaves the building, and use this as a guide to the depth of the trench from the level line throughout its course.

Answer 3

Elevations of buried piping are generally given from the "invert elevation" . The pipe "invert" simply refers to the inside bottom surface where the liquid flows. In gravity systems, the elevation is generally given at the highest end of the pipe, and then a percent slope is provided so that you may calculate the invert of the outlet. I any case, elevations of pipes and structures are given in feet above sea level (in most parts of the country). If you are able to establish a benchmark (known elevation in feet above sea level) somewhere close to the pipe invert, all you need to do is measure from the height of the know elevation to the invert of the pipe and you will have your elevation. This is typically done with a transit or lock level.

Answer 4

You have to run a level circuit from a known benchmark to the sewer you are interested in to compute the elevation.

Perhaps you meant something different.