a. All sanitary sewers shall be laid on a slope which will produce a mean velocity when flowing full of at least two (2) feet per second based on Manning's formula using minimum roughness coefficient of 0.013 or the pipe manufacturer's recommendations, whichever is greater.

b. The minimum acceptable slopes for various pipe sizes are listed below:

c. Gradients greater than those shown above are desirable and are particularly recommended on the upper ends of lateral sewers.

d. Sewers shall be laid with uniform slope and alignment between manholes.

e. Grades (slopes) shall be determined to the pipe invert at the edge of the manhole and lengths to the center of the manhole.

f. The difference between the inlet pipe slope (Si) and outlet pipe slope (So) at any manhole shall not exceed 25 percent.

g. Sewers on slopes of 20 percent or more shall be anchored with concrete anchor walls or other restraining methods approved or specified by the City.

h. Where velocities greater than fifteen (15) feet per second are attained, the pipe material shall be ductile iron and special provision shall be made to protect manholes against erosion and displacement by shock. This may be accomplished by installing one additional manhole to decrease the slope or to split a 90° horizontal direction change into two 45° incremental changes.