What is the Difference Between a Drop Manhole and a Regular Manhole?

A drop manhole is used in areas with a steep slope when one or more of the inlet pipes has an invert elevation significantly higher than the invert of the outlet pipe. Typically the invert elevation of the "stop" end of the inlet pipe is set to the invert elevation of the manhole. However, in the case of a drop manhole, the stop invert of the pipe is not set to the manhole invert elevation but is at a significantly higher elevation.

The following illustration shows a drop manhole.

Figure 15-1: Drop Manhole

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