Choosing Where to Apply Additional Storage
You have the option to apply additional storage to the shaft and chamber of the manhole in any proportion. So you could apply all the storage to the shaft, or the chamber, or a percentage to both.
- Shaft Storage - Applying the additional storage to the shaft will mean that the storage has no hydraulic effect until the water level reaches above the level of the chamber roof. In most cases this will be appropriate. The additional small pipes that feed into a manhole from nearby properties often flow in close to the ground surface, and not at the level of the main sewers.
- Chamber Storage - Applying the additional storage to the chamber will mean the storage has hydraulic effects at all flow levels, with the hydrograph being attenuated as it passes through the manhole. This may be appropriate if the additional storage comes from small pipes that flow directly into the main sewers, rather than joining at the manhole.
In most cases, it will be appropriate to apply the additional storage in the shaft. However, you may choose to apply it in the chamber, or split between the two, depending on the actual construction of the manhole and surrounding pipes.
