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How is the headloss for a weir calculated in the control structure for the storm and sewer products? How is the headloss for a submerged weir calculated?
The solver uses the traditional weir equation and the effective head, which is the difference between upstream and downstream water elevation (or downstream and upstream, if flow is reversed), to calculate the weir flow. If the weir is not submerged the effective head is the difference of water elevation and weir crest elevation.
Because of the assumptions of this calculation, the headloss for a submerged weir is not calculated. If you need to make adjustments to compensate for headloss, you can adjust the weir coefficient.