The correct answer is D. All the above.
The gradient of a sewer is the slope of the sewer pipe. It is important to have a proper gradient in order to ensure that sewage flows smoothly and does not back up. The gradient of a sewer depends on the following factors:
- Velocity of flow: The faster the velocity of flow, the steeper the gradient needs to be in order to prevent sewage from backing up.
- Diameter of the sewer: The larger the diameter of the sewer, the less steep the gradient needs to be.
- Discharge: The higher the discharge, the steeper the gradient needs to be.
In general, the gradient of a sewer should be between 0.001 and 0.002. This means that for every 100 feet of sewer pipe, the pipe should slope down by 1 inch. If the gradient is too steep, sewage can erode the pipe and cause leaks. If the gradient is too shallow, sewage can back up and cause flooding.
It is important to calculate the correct gradient for a sewer before it is installed. This can be done by using a hydraulics calculator or by consulting with a civil engineer.