What does it indicate if the level of the upstream manhole is greater than the level of the downstream manhole?

When the level of the upstream manhole is higher than that of the downstream manhole, it suggests that there is a restriction or blockage in the system between the two manholes. In a typical fluid flow scenario, liquids flow from higher to lower elevations. If the upstream level is elevated while the downstream level remains lower, it indicates that something is preventing the normal flow, causing a back-up of liquid.

This condition often points to a physical obstruction in the piping, such as debris, sediment buildup, or potential damage to the system, which could be limiting flow. It highlights an issue that requires further investigation to ensure that the water flow can resume to its expected, unobstructed state.

Alternative interpretations might suggest that issues exist either upstream or downstream, but they do not align with the observed difference in water levels. The situation is specifically indicative of a restriction impeding flow between the two manholes, directly supporting the conclusion that a blockage is present in that portion of the system.