Orifice Area Unsubmerged Hydraulics
To develop a continuous discharge rating relation for an orifice structure, it is necessary to handle flow situations in which the orifice opening is not fully submerged. For area-based orifice calculations, Drainage and Utilities performs a straightline interpolation, setting the flow by multiplying the full flow, Qt, (at unsubmerged head, Ht) by the ratio of actual H to Ht.
Qu | = | unsubmerged discharge | |
Qt | = | full discharge at Ht | |
Hu | = | unsubmerged head | |
Ht | = | height of the orifice opening |
Heads are measured from the opening invert or from the controlling tailwater, whichever is greater.