Sewer Overflow formula (Water Overlay): Difference between revisions
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* B<sub>o</sub> = The height | * B<sub>o</sub> = The [[terrain height (Water Overlay)|surface height]] at the centerpoint of the sewer overflow, relative to {{datum}}. | ||
* B<sub>s</sub> = The assumed surface height of the sewer, relative to {{datum}}. | * B<sub>s</sub> = The assumed surface height of the sewer, relative to {{datum}}. | ||
* w<sub>o</sub> = The water level at the sewer overflow's exit, relative to {{datum}}. | * w<sub>o</sub> = The [[Surface water level formula (Water Overlay)|water level]] at the sewer overflow's exit, relative to {{datum}}. | ||
* w<sub>s</sub> = The water level | * w<sub>s</sub> = The water level in the sewer, relative to {{datum}}. | ||
* H<sub>o</sub> = The height of the sewer overflow threshold in the sewer. | * H<sub>o</sub> = The height of the sewer overflow threshold in the sewer. | ||
Revision as of 11:18, 14 June 2019
Overflow from the sewer is calculated for the entirety of the sewer, and the single attached sewer overflow.
The sewer base height is located at the height indicated by the sewer overflow:
- Bs = Bo
The water level at the sewer is then:
- ws = hs + Bs
The sewer overflow threshold height Ho within the sewer is calculated as:
- Ho = Hs * To
Water only flows out of the sewer if:
- hs > Ho and
- hs + Bs > wo
The amount that can overflow relies on both the water level at the sewer overflow itself as well as the sewer overflow threshold and the stored sewer water:
- Δh = min ( hs - Ho , ws - wo)
The flow is then calculated with the SEWER_OVERFLOW_SPEED attribute of the sewer overflow and the maximum speed with which water can flow through the sewer overflow:
- Δw = min( Δh, Δt * qo / As)
The amount of water added to the exit cell(s) of the sewer overflow:
- Qt = Δw * As
where:
- Bo = The surface height at the centerpoint of the sewer overflow, relative to datum.
- Bs = The assumed surface height of the sewer, relative to datum.
- wo = The water level at the sewer overflow's exit, relative to datum.
- ws = The water level in the sewer, relative to datum.
- Ho = The height of the sewer overflow threshold in the sewer.
- hs = The sewer water height.
- Hs = The SEWER_STORAGE attribute of the sewer area, the maximum water height allowed in the sewer.
- Δw = Water level change in the sewer, due to sewer overflow.
- Δt = Computational timestep.
- As = The surface area of the sewer.
- qo = The SEWER_OVERFLOW_SPEED attribute of the sewer overflow.
- To = The SEWER_OVERFLOW_THRESHOLD, the threshold factor indicating the fraction of the sewer's storage height that is blocked by the sewer overflow 's threshold.
- Qt = The amount of water pumped out of the sewer through the sewer overflow.
Notes
- The sewers area is counted as the amount of sewered grid cells times the size of a grid cell.
- The sewer's height relative to datum is not defined in the Sewer itself. It is relative to the sewer overflow and determined by the SEWER_OVERFLOW attribute of the overflow.
See also
