When connecting a smaller sewer to a larger one, what should be done to the invert of the larger sewer to maintain the same energy gradient?

In the context of connecting a smaller sewer to a larger sewer, lowering the invert of the larger sewer is necessary to maintain the same energy gradient. When two pipes of different diameters are connected, the flow characteristics can change. The larger sewer typically has a greater cross-sectional area and, thus, a lower velocity of flow compared to the smaller sewer when both are flowing full.

To maintain an equivalent energy gradient, which is crucial for ensuring that the flow remains efficient and prevents issues such as backflow or stagnant areas, the invert of the larger sewer has to be adjusted. Lowering it helps in accommodating the incoming flow from the smaller sewer without causing a significant drop in the energy head. This adjustment allows for a smooth transition between the two pipelines, which promotes uniform flow and minimizes turbulence or energy losses that could occur if the connection were not appropriately made.

Proper management of the invert levels not only supports the hydraulic design principles but is also essential for the long-term functionality of the sewer system, ensuring that all wastewater is carried away effectively and reducing the risk of blockages or overflows.